The Joan Mott Prize Lecture
The integrated response to hypoxia: from circulation to cells
- JANICE M. MARSHALL
-
- Published online by Cambridge University Press:
- 30 August 2019, pp. 449-470
-
- Article
- Export citation
-
I guess everyone who is asked to give one of the Physiological Society's Prize Lectures feels honoured, but I feel particularly honoured to have been asked to give the Joan Mott Prize Lecture. I first met Joan Mott in 1980 at the Oxford meeting of the Physiological Society. I had just given a communication on baro- and chemoreceptor influences on the cardiovascular system and she came to introduce herself to me. I was a young lecturer at the time, and still felt a rather junior member of the Society. I had seen Joan Mott at many Physiological Society meetings. I had heard her give communications and had heard her entering into lively discussions after papers, and I knew she was a well respected scientist. I was therefore flattered that she should have come to talk to me about my work. After that we met at many Physiological Society meetings and she always made a point of asking how our research was going and we would talk of common interests. To me this is one of the most important aspects of Physiological Society meetings, that young and older members of the Society can rub shoulders with one a nother and discuss science openly with no barriers. Joan Mott had an influence on me that I have tried to remember as I have become a more senior member of the Society.
Research Article
Effect of extracellular cations on the inward rectifying K+ channels Kir2.1 and Kir3.1/Kir3.4
- J. M. OWEN, C. C. QUINN, R. LEACH, J. B. C. FINDLAY, M. R. BOYETT
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 471-488
-
- Article
- Export citation
-
The effects of Ba2+, Mg2+, Ca2+ and Na+ as blocking ions were investigated in 90 and 10 mM extracellular K+ solutions on the cloned inward rectifying K+ channel Kir2.1 expressed in Xenopus oocytes. Some data were also obtained using another inward rectifying K+ channel Kir3.1/Kir3.4. The addition of Ba2+ caused a concentration-, voltage- and time-dependent block of both channels. Decreasing the extracellular K+ concentration augmented the block. The data suggest that Ba2+ blocks the channels by binding to a site within the channel pore and that the electrical binding distance, δ, of the site is significantly different for Kir2.1 and Kir3.1/Kir3.4 ([eqv] 0·38 and [eqv] 0·22, respectively). Mg2+ and Ca2+ caused an instantaneous concentration- and voltage-dependent block of both channels. With Kir2.1, decreasing the K+ concentration augmented the block. The voltage dependence of the block was less than that of Ba2+ (δ, [eqv] 0·1), indicating a more superficial binding site for these ions within the channel pore. The affinity of the channels for Mg2+ and Ca2+ was [eqv] 1000-fold lower than that for Ba2+. Addition of Na+ resulted in a concentration-, voltage- and time-dependent block of Kir2.1, similar to that observed with Ba2+. The competition between the blocking cations (for Kir2.1: Ba2+, Mg2+, Ca2+; for Kir3.1/Kir3.4: Ba2+) and extracellular K+ suggests that the binding sites for the blocking cations may be sites to which K+ binds as part of the normal passage of K+ through the channels. It is possible that under normal physiological conditions naturally occurring extracellular cations may partly block the two inward rectifying K+ channels.
Activation of ionic channels by deoxycholate in frog and human cell lines
- A. C. MAURÍCIO, K. T. G. FERREIRA
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 489-499
-
- Article
- Export citation
-
Humans, after extensive ileal resection, frequently suffer from diarrhoea, which may be due to an increased delivery of deoxycholate (DOC) to the large intestine. In the frog skin the addition of DOC (0·5 mM) to the apical side induced the activation of amiloride-sensitive Na+ channels and an increase in the unidirectional Cl- fluxes. Here we used two established cell lines (A6 and Caco2) to study the effect of DOC on ion channels at cell and membrane level using the patch-clamp technique. In A6 cells subcultured directly on Petri dishes and studied in the whole-cell configuration, DOC induced an increase in cell conductance of 110·3 ± 4 pS pF-1 (N = 8) which was reduced to 89 ± 14 pS pF-1 (N = 8) by the addition of DIDS (0·5 mM). The absolute values of these two effects were not statistically different (P < 0·2). In Caco2 cells, the addition of DOC (0·5 mM) induced, after 1 min, an increase in cell conductance of 583 ± 16 pS pF-1 (N = 8) which was reduced to 560·4 ± 16 pS pF-1 (N = 8) by DIDS (0·5 mM) and N-phenylanthranilic acid (DPC; 0·5 mM). The two values were not statistically different (P < 0·4). In Caco2 cells subcultured under the same conditions, DOC induced an increase in cell conductance of 1710 ± 64 pS pF-1 (N = 6). Subsequent addition of amiloride (0·1 mM) reduced the cell conductance to 1558 ± 33 pS pF-1 (N = 6). These two mean values were statistically different allowing for an error of the second kind < 0·05. In cells in which DOC produced a conductance increase of 1010 ± 10 pS pF-1, gadolinium (0·5 mM) induced a fall in cell conductance of 1800 ± 10 pS pF-1. In Caco2 cells, addition of DOC (0·5 mM) to the bath reversibly induced the appearance of or an increase in channel activity in patches studied in cell-attached and excised inside-out configuration. In inside-out experiments (N = 13) DOC (0·5 mM) induced the appearance of channel activity with conductances and reversal potentials (Er) of 27·7 ± 1·9 pS and 0·8 ± 5·7 mV, respectively. In cell-attached patches (N = 13) these values were 24·9 ± 4·4 pS and -18·1 ± 6·4 mV. In excised inside-out patches from Caco2 cells, subjected to electrochemical gradients for Na+, K+ and Cl-, (+85, -85 and 0 mV, respectively), addition of DOC also induced an increase in the baseline conductance and a shift in the reversal potential from values around +25 mV to values around 0 mV. Bile salts activated both anionic and cationic channels and did not require the presence of intracellular factors for these effects. We suggest that they act at the membrane level.
High activity K+ channels in rat hippocampal neurones maintained in culture
- K. T. WANN*, P. A. GOODWIN, C. D. RICHARDS
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 501-514
-
- Article
- Export citation
-
A channel was identified in cell-attached recordings in rat hippocampal neurones maintained in culture. This channel, which was highly active at the resting membrane potential, was present in most (73 %) patches studied. The channel was characterized by long duration openings and a high open probability (Po, mean value 0·73 at -70 mV) at negative patch potentials with mild voltage dependence over the range -40 to -120 mV. It showed inward rectification. There were up to five active channels in cell-attached recordings in experiments where the cells were bathed in sodium-containing Locke solution. The single channel conductances in cell-attached recordings with 140 or 40 mM K+ in the patch pipette were 26 and 12 pS, respectively. The channel was therefore selective for K+ over Na+. The channel was not permeable to Rb+ ions. The single channel conductance was 24 pS in excised inside-out patches bathed in symmetrical K+ (140 mM) solutions. Examination of the channel kinetics revealed that both the open and closed time distributions could be fitted by the sum of three exponentials, there being no pronounced voltage sensitivity between -60 and -120 mV. The 26 pS K+ channel was insensitive to extracellular TEA, apamin, 4-AP and dequalinium. Neither was it sensitive to intracellular Ca2+. Extracellular Ba2+ was effective in reversibly blocking the channel, the IC50 being 2.0 mM. There was no obvious effect of bath application of the K+ channel opener, lemakalim, or a cAMP analogue. This channel appears to contribute a significant proportion (at least 30 %) of the resting conductance in these neurones.
Chemoattractant- and mitogen-induced generation of reactive oxygen species in human lymphocytes: the role of calcium
- NELSON N. ORIE, WALTER ZIDEK, MARTIN TEPEL
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 515-520
-
- Article
- Export citation
-
This study examined the role of calcium in the generation of reactive oxygen species (ROS) in human lymphocytes activated by the chemoattractant formyl-Met-Leu-Phe (fMLP) and the T-cell mitogen phytohaemagglutinin (PHA). The concentrations of cytosolic calcium ([Ca2+]i) and ROS were monitored simultaneously with a fluorescence spectrophotometer after the cells had been incubated in fura-2 (calcium-sensitive dye) and 2',7'-dichlorofluorescein diacetate (DCF-DA, ROS-sensitive dye). The lymphocytes were stimulated with fMLP (200 nmol l-1) or PHA (10 µmol l-1) in the absence and presence of extracellular calcium. A dose-response test was also conducted for extracellular calcium. fMLP and PHA significantly increased both [Ca2+]i (P < 0.001) and ROS concentrations (P < 0.001) above the control levels in the presence of extracellular calcium. However, such increases were abolished in the absence of extracellular calcium, suggesting total dependence of the responses to both fMLP and PHA on transplasma-membrane calcium influx. There were also graded increases in ROS with increasing concentrations of extracellular calcium. The results show that transplasma-membrane calcium influx is essential for fMLP- and PHA-induced generation of reactive oxygen species in human lymphocytes.
The role of Na+-H+ exchange in fluid and solute transport in the rat efferent ducts
- L. A. HANSEN, J. CLULOW, R. C. JONES
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 521-527
-
- Article
- Export citation
-
In vivo microperfusion techniques were used to investigate the role of Na+-H+ exchange in the efferent ducts of the rat. Individual efferent ducts were perfused with a Krebs-Ringer bicarbonate solution (KRB) containing 0, 1, 3, 5 or 7·5 mM amiloride. Concentrations of 1-5 mM amiloride inhibited fluid reabsorption from the efferent ducts in a linear dose-dependent manner with an apparent Km of 3 mM. Inhibition was maximal at 5 mM with reabsorption reduced by about 70 %. The effects of amiloride were completely reversible and there was little effect of amiloride on luminal osmolality and concentrations of Na+, Cl- or K+. It is concluded that Na+-H+ exchange is one of the principal mechanisms responsible for fluid and electrolyte reabsorption in the efferent ducts and offers a means by which the efferent ducts are able to achieve flow-dependent, autoregulated fluid reabsorption.
Effects of changes in pH and PCO2 on wall tension in isolated rat intrapulmonary arteries
- MICHELE SWEENEY, RONAN G. O'REGAN, PAUL McLOUGHLIN
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 529-539
-
- Article
- Export citation
-
We examined mean (± S.E.M.) changes in wall tension in isolated rat intrapulmonary arteries on switching from control conditions (pH 7.38 ± 0.01; PCO2, 34.4 ± 0.5 mmHg) to hypercapnic acidosis (pH change, -0.24 ± 0.01; PCO2 change, +27.5 ± 0.9 mmHg), isohydric hypercapnia (pH change, -0.02 ± 0.01; PCO2 change, +28.5 ± 0.8 mmHg) and normocapnic acidosis (pH change, -0.24 ± 0.01; PCO2 change, -0.5 ± 0.3). Arteries were submaximally preconstricted with prostaglandin F2alpha; and changes in tension are expressed as a percentage of the 80 mM KCl-induced contraction (%Po). Mean changes in wall tension on switching to hypercapnic acidosis (+4.4 ± 3.7 %Po), isohydric hypercapnia (+1.9 ± 2.2 %Po) and normocapnic acidosis (-1.5 ± 1.9 %Po) were not significantly different from the change observed on switching to control conditions (+3.5 ± 1.1 %Po), and were unaltered by endothelial removal. In isolated carotid preparations, the change in tension in isohydric hypercapnia (-6.8 ± 7.1 %Po) was not significantly different from that observed in control switches (+8.6 ± 3.2 %Po). Significant reductions in tension (P < 0.001) were observed in hypercapnic (-42.9 ± 7.8 %Po) and normocapnic acidosis (-36.4 ± 9.0 %Po). These data suggest that intrapulmonary arteries are resistant to the vasodilator effects of extracellular acidosis observed in systemic (carotid) vessels.
Inhibition of mucosal glycylsarcosine uptake by acetate in rat distal small intestine
- E. SCHARRER, I. AMSTUTZ, B. GRENACHER
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 541-548
-
- Article
- Export citation
-
Acetate deriving from microbial fermentation may occur at considerable concentrations in the distal small intestine, where it appears to be absorbed by two different mechanisms: acetate-HCO3- exchange and non-ionic diffusion. Whether acetate affects absorption of other nutrients at this intestinal site is not known. Therefore the influence of acetate (30 mmol l-1) on oligopeptide absorption was studied using an in vitro mucosal uptake technique allowing measurement of substrate uptake across the brush border membrane (BBM). Acetate significantly inhibited mucosal uptake of 14C-labelled glycylsarcosine (Gly-Sar) at pH 6 and pH 7 in the presence of sodium. No inhibition occurred in the absence of sodium. Both acetate and the absence of sodium decreased Vmax of mucosal Gly-Sar uptake without substantially affecting the apparent Km value. Since it is well established that Vmax of peptide transport across the intestinal BBM depends on the size of the transmembrane H+ gradient as a driving force the present findings are in accordance with the assumption that acetate inhibits peptide absorption by attenuating the H+ gradient across the BBM, which depends on the presence of sodium.
Insulin sensitivity, clearance and release in kininogen-deficient rats
- JACQUES DAMAS*, VICTOR BOURDON, PIERRE J. LEFEBVRE
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 549-557
-
- Article
- Export citation
-
Insulin sensitivity of kininogen-deficient rats was compared with that of normal rats using euglycaemic hyperinsulinaemic glucose clamping. Anaesthetized animals were infused with 2-50 mU kg-1 min-1 of insulin and the glucose infusion rates needed to maintain euglycaemia were determined. Maximum glucose uptake, insulin sensitivity index and insulin clearance were reduced in kininogen-deficient rats. Captopril increased the amount of glucose needed to maintain euglycaemia during infusion of 2 and 10 mU kg-1 min-1 of insulin in normal rats, but had no effect in kininogen-deficient rats. Anaesthetized rats of both strains were given an intraperitoneal injection of glucose and the evolution of blood glucose was followed for 120 min. The peak increase was higher in kininogen-deficient rats. Similar larger increases in blood glucose were observed after glucose injection in normal rats previously treated with HOE 140, a bradykinin B2 receptor antagonist. After glucose injection, plasma insulin increased in both groups of rats but reached lower levels in kininogen-deficient animals. These results suggest that bradykinin is involved not only in the clearance of glucose and insulin by the tissues during insulin infusion but also that bradykinin can affect the release of insulin after a glucose load.
Vagotomy suppresses cephalic phase insulin release in sheep
- C. B. HERATH, G. W. REYNOLDS, D. D. S. MACKENZIE, S. R. DAVIS, P. M. HARRIS
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 559-569
-
- Article
- Export citation
-
The effect of selective vagotomy of the abomasum, pylorus, duodenum and liver on insulin release during the cephalic phase of digestion was investigated in wethers and lactating ewes. Electrical stimulation of the cervical vagus nerves was carried out to test the completeness of the vagotomies performed. In experiment 1, using wethers, the abomasal, pyloric and duodenal branches (ADV; n = 7) or the hepatic, abomasal, pyloric and duodenal branches (HADV; n = 10) of the ventral and/or dorsal vagus nerves were cut; a third group of wethers underwent sham-operation (SO; n = 8). In experiment 2, vagotomy (ADV; n = 5) or sham-operations (SO; n = 5) were carried out in lactating ewes. Jugular blood was drawn before and after presentation of food for glucose and insulin determination (experiments 1 and 2) or before, during and after the electrical stimulation of the peripheral ends of the cut cervical vagus nerves in randomly selected lactating ewes (experiment 3: ADV = 3, SO = 3) and wethers (experiment 4: ADV = 4, HADV = 4, SO = 4), for determination of insulin only. Presentation of food caused an immediate and significant (P < 0.05) rise in plasma insulin levels in SO animals compared with ADV or HADV wethers (experiment 1) or ADV ewes (experiment 2) without any significant change in blood glucose concentrations. In comparison with the SO group the baseline-corrected areas under the insulin response curve were significantly (P < 0.05) smaller for the respective vagotomized groups for periods 1-2, 2-4 and 4-6 min (experiment 1) and 1-2 and 2-4 min (experiment 2) after presentation of food. Total area under the response curve for 10 min was significantly (P < 0.05) lower (experiment 1) and tended (P < 0.10) to be lower (experiment 2) for the vagotomized groups compared with that of the control groups. Direct electrical stimulation of the cervical vagus nerves raised plasma insulin concentrations to significantly (P < 0.05) higher levels in the SO ewes but not in the ADV ewes (experiment 3). It was also evident that in experiment 1, HADV did not have any additive effect over that achieved by ADV alone. These results indicate that the vagal innervation of the gut mediates insulin release during the cephalic phase of feeding in sheep. It is concluded that insulin secretion from the pancreatic β-cells in response to either food-related reflex activation of the vagal nuclei in the hypothalamus or direct cervical vagus nerve stimulation is mediated through the vagal efferent fibres carried in the abomasal, pyloric and duodenal branches of the vagus nerves in sheep.
Cardiovascular changes associated with dehydration and drinking in unrestrained, lactating goats
- KERSTIN OLSSON, ERIKA CARLSSON
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 571-578
-
- Article
- Export citation
-
The aim of this study was to investigate if the alertness connected with seeing water increased arterial blood pressure and heart rate to the same extent as the act of drinking, and if ingestion of warm water caused a different effect compared with ingestion of cool water on these cardiovascular variables. Seven goats of the Swedish domestic breed (Capra hircus) were used in a cross-over design. The animals were dehydrated for 24 h. They were allowed to watch water being prepared for 11-16 min, after which they were given access to warm (35°C) or cool (15°C) water. The goats drank 6.86 ± 0.36 l of the warm water and 4.54 ± 0.35 l of the cool water (P < 0.05) within the first hour. The arterial blood pressure, heart rate and activity of the animals were registered by an implanted telemetric device. Dehydration did not affect the cardiovascular variables, except before feeding in the morning, when the heart rate accelerated faster in dehydrated goats. Heart rate increased abruptly when dehydrated goats saw water being prepared, remained at the increased level during drinking and then slowly declined. It increased again during the afternoon feeding, to a level similar to that on control days, but between 18.00 and 06.00 h the heart rate was higher than during control nights. Blood pressure did not change when the goats saw water, but increased when they drank. On the morning following rehydration, the rise in heart rate in response to feeding was delayed compared with that during control and dehydration periods. It is concluded that seeing water caused arousal in the goats, resulting in an accelerated heart rate. The additional rise in blood pressure during the act of drinking appears to be a combination of excitement and sensory inputs from the pharyngeal region, causing a temporary activation of the sympathetic nervous system.
Effects of variations in live weight gain on bone growth and composition and on markers of bone turnover in lambs
- M. L. F. NICODEMO, D. SCOTT, W. BUCHAN, A. DUNCAN, S. P. ROBINS
-
- Published online by Cambridge University Press:
- 03 January 2001, pp. 579-587
-
- Article
- Export citation
-
Growing lambs were fed the same diet at intakes supporting mean live weight gains of 0·1, 0·2 and 0·3 kg day-1, representing slow, intermediate and fast growth groups, respectively. The effects on bone growth and composition, and on blood and urinary bone marker concentrations or excretion rates were monitored. Compared with the slow-growing lambs, the higher intake group grew twice as fast, had higher rates of bone growth (indicated by external metatarsal length), and larger and heavier bones at slaughter. Bones from fast-growing animals had higher collagen and deoxypyridinoline concentrations, and lower Ca:collagen, Ca :P and pyridinoline : deoxypyridinoline ratios, indicating a less mature bone compared with the slow-growing lambs. Bone growth rate had no effect on plasma osteocalcin, bone-specific alkaline phosphatase or growth hormone concentrations, nor on the urinary excretion of pyridinoline and deoxypyridinoline. The results for plasma markers may be explained by an increase in blood volume linked with increased body weight.
Book Review
Review of Medical Physiology, 18th edn. By William E. Ganong. Pp. 890.
- Ron Maughan
-
- Published online by Cambridge University Press:
- 30 August 2019, p. 599
-
- Article
- Export citation
-
I well remember Ganong's Review of Physiology from my days as an undergraduate student of physiology: it was then in about its seventh edition (am I really that old?). Although it was the recommended text at second year level, it was not my first choice for essay or practical write-up material or for last minute pre-exam revision - probably the only times that the average undergraduate ever consults a textbook. Now, many years later the same book has appeared in its eighteenth edition, and the question is would I use it now, and would it be my recommended student text.