Renal function was assessed in unrestrained conscious rats during either their active period (i.e. the hours of darkness) or their inactive period. On the following day, measurements were repeated after Inactin anaesthesia and preparation for clearance studies. In rats anaesthetized during their active period, preparation for clearance studies had no effect on inulin clearance (used as a measure of glomerular filtration rate), lithium clearance (used as an estimate of endproximal fluid delivery) or fractional lithium excretion. In rats anaesthetized during their inactive period, the same procedures resulted in increases in all three variables, to reach values indistinguishable from those in animals studied during their active period. In both groups of rats there were increases in the fractional reabsorption of sodium and water in the distal nephron and in the urinary excretion of potassium. It is concluded that in anaesthetized rats prepared for clearance studies, rates of glomerular filtration and proximal tubular reabsorption (as indicated by lithium clearance) are similar to those in conscious animals during their active period.
Quarterly Journal of Experimental PhysiologyVolume 74, Issue 6 p. 1051-1069 ArticleFree Access REVIEW OF ELECTRON MICROSCOPIC EVIDENCE FAVOURING VESICLE EXOCYTOSIS AS THE STRUCTURAL BASIS FOR QUANTAL RELEASE DURING SYNAPTIC TRANSMISSION John E. Heuser, John E. Heuser Department of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USASearch for more papers by this author John E. Heuser, John E. Heuser Department of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Avenue, St Louis, MO 63110, USASearch for more papers by this author First published: 12 November 1989 https://doi.org/10.1113/expphysiol.1989.sp003333Citations: 73AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume74, Issue6November 12, 1989Pages 1051-1069 RelatedInformation
Action potentials were recorded from guinea-pig ventricular cells and contraction recorded by an optical technique. When the plateau of a single action potential was depolarized (by 70-120 pA applied 100 ms after the upstroke for 100 ms), contraction associated with the following normal action potential was potentiated. This potentiation was not seen in cells exposed to 10 mM-caffeine. The observations are consistent with potentiation of subsequent contraction by increased loading of caffeine-sensitive calcium stores, as a consequence of reduced Ca2+ extrusion or possibly Ca2+ entry via Na+-Ca2+ exchange during a depolarized plateau.
The existence of polyneuronal innervation in adult rat skeletal muscle reported by Taxt (1983) has been reinvestigated. The extent of polyneuronal innervation was measured by intracellular recording in cut muscle fibre preparations. Only fibres in which spontaneously occurring miniature end‐plate potentials were visible were tested for the presence of multiple inputs. Only one in sixty‐nine fibres penetrated was found to have more than one axonal input. High‐threshold, low‐amplitude end‐plate potentials were sought, but none was found. Thus we were unable to find any evidence for extensive polyneuronal innervation persisting in rats of 40 days of age.
The transport of K+ (using 86Rb as tracer) by lactating rat mammary tissue slices has been studied in order to seek evidence for Na+-K+-Cl- co-transport. Potassium transport was inhibited by furosemide; the locus of inhibition was at a site other than the Na+:K+ pump. Replacing medium Cl- with NO3 reduced the bidirectional movement of K+; moreover, furosemide was without effect in a Cl- -free medium. Sodium replacement by N-methyl-D-glucamine acted to reduce the loop diuretic-sensitive component of K+ uptake whilst concomitantly increasing K+ influx via an ouabain- and furosemide-resistant pathway. Potassium efflux was found to be transiently stimulated by Na+ ions; this was attenuated by furosemide. Potassium egress was markedly increased via a furosemide-insensitive pathway when salicylate was used to replace Cl-. The results are consistent with furosemide-sensitive Na+-K+-Cl- co-transport.
Fluid balance and thermoregulation were studied during an acute heat load (maximal daily temperature, 38 +/- 1 degrees C; night temperature 27 +/- 1 degrees C) in six goats during lactation and non-lactation. The goats had free access to water for 1 day, followed by 29.5 h of water deprivation and then water was returned. With water available the goats increased water intake and urinary and milk water losses, while plasma and milk osmolality decreased. Water deprivation caused plasma osmolality and vasopressin concentration to increase most in lactating goats. Milk osmolality rose to values similar to plasma osmolality. Plasma cortisol increased in lactating goats at the end of dehydration. Renal Na+ excretion increased during dehydration in lactating goats. Evaporative heat loss was larger in lactating goats when hydrated, but became less than in non-lactating goats during dehydration. Lactating goats exhibited higher respiratory frequency and rectal temperature than non-lactating goats. In conclusion, our results show that goats increase the water turnover during heat stress if allowed to drink ad libitum, but when they are deprived of water lactating goats reduce water loss in urine, milk and by evaporation, and rectal temperature reaches higher levels than in non-lactating animals. This saving of water could allow milk production to be maintained for a longer time during heat stress.
Isosmotic transport of fluid across epithelial cell layers occurs by intraepithelial mechanisms that are not fully understood. Newer methods of measuring water flows across epithelia with higher resolution should now permit some key issues regarding solute-linked water transport to be clarified. Unstirred-layer effects are not likely to be serious sources of error in these measurements with judicious choice of experimental conditions. Progress in ultrastructural stereology has shown that in the proximal tubule most of the transporting membrane is located in the basal aspects of cells, making models based on a hyperosmolar lateral compartment less relevant. The current models of simple transcellular osmosis, though appealing for this simplicity, fail to account for some major experimental findings. Experimental design and methodological limitations have not yet achieved rigorous testing of whether or not epithelia can produce a perfectly isosmotic absorbate without any transepithelial driving forces. A better understanding of the mechanism of translocation of water through the lipid bilayer, the plasma membrane proteins, and special membrane structures like the tight junctions would significantly contribute to our knowledge of the mechanisms and intraepithelial routes by which water is transported by epithelia.
Monolayers of canine kidney (MDCK) and human lower intestinal (T84 and HCT-8) cell lines generated significant transepithelial electrical resistance (700-5000 omega cm2). Electrical integrity was maintained upon acidification of the apical and/or basolateral surfaces to pH 3.0, and this was associated with increased transepithelial electrical resistance, and generation of a potential difference at pH less than 4.5. These results indicate that resistance to acid is a general phenomenon of epithelial layers, and that monolayers of epithelial cells, including those of human origin, are a homogeneous and simple model for studying epithelial barrier function in vitro.
The concentration of Mg, Na and K in the rumen and plasma of each of four sheep has been studied while test solutions were infused into their jugular veins for 8 h. The experiment was designed as a 4 x 4 Latin square with: treatment 1: diet only; treatment 2: diet + 5% dextrose infusion; treatment 3: diet + 5% dextrose infusion containing aldosterone; treatment 4: diet + 5% dextrose infusion containing aldosterone and potassium canrenoate (a specific inhibitor of the action of aldosterone). Rumen and blood samples were collected every hour during the 8 h treatment period and for the subsequent 4 h. Rumen volume and outflow rate were estimated using an intra-ruminal infusion of [14C]Cr-EDTA throughout the collection period. The aldosterone infusion significantly (P less than 0.001) increased the concentration of Mg in the rumen while rumen volume and outflow rate remained unchanged. Plasma concentrations of Mg and K were significantly (P less than 0.001 and P less than 0.05, respectively) lower during the aldosterone infusion while plasma Na concentrations did not vary significantly. The results are discussed in relation to hypomagnesaemic tetany.
Intracellular pH (pHi) was measured at the tips of extending neurites and in the corresponding cell bodies of single cultured mouse neuroblastoma (N2A) and rat pheochromocytoma cells (PC12) using the fluorescent dye 2,3-di-cyanohydroquinone (DCH). It was observed that pHi at the tip of an extending neurite was consistently 0.2-0.3 pH units higher than pHi in the cell body. Experiments performed on whole cells to establish the types of cellular mechanism which could be responsible for such regional differences demonstrate the presence of Na+-H+ exchange and Cl- HCO3- exchange in these cells. Since regional variations in Ca2i+ have been reported between neurites and the cell body, experiments were performed to examine the possible interactions between pHi and Ca2i+. Intracellular calcium was measured using the fluorescent Ca2+-sensitive dye Indo-1. An increase in pHi, on application of NH4Cl, resulted in a transient elevation of Ca12i+. On subsequent acidification, on removal of NH4Cl, there was a further transient increase in Ca2i+. These changes in Ca2i+ were also present in solutions with low calcium suggesting that Ca2i+ is mobilized from within the cell. The results are discussed in terms of possible mechanisms whereby the extension and retraction of cell processes could be influenced by Ca2i+ and modulated by pHi.
We have measured the intracellular pH (pHi) of single isolated rat pancreatic acini using the fluorescent dye dicyano-hydroquinone (DCH). Steady-state pHi was unaffected by either acetylcholine (10 microM), caerulein (10 nM) or secretin (1 nM), or by the anion exchange inhibitor DIDS (1 mM) and only changed by 0.32 units when extracellular pH was varied over the range from 6.8 to 8.4. However, replacing extracellular chloride with gluconate, such that the final bath chloride concentration was less than 20 mM, caused a marked alkalinization of pHi to a new steady-state value. The rate of pHi alkalinization under these conditions was bicarbonate-dependent, blocked by pre-incubation of the acini with 1 mM-DIDS, but unaffected by removal of extracellular sodium. These observations are consistent with the presence of a Cl- -HCO3- exchanger on rat pancreatic acinar cells. Since DIDS had no effect on steady-state pHi the anion exchanger is unlikely to play a role in pHi regulation. However, rat pancreatic acini secrete a NaCl-rich fluid and the Cl- -HCO3- a exchanger might function in parallel with Na+-H+ exchangers to provide a mechanism for chloride accumulation across the basolateral membrane of the acinar cells.
Vasoactive intestinal peptide (VIP) has been shown to stimulate adenylate cyclase activity in plasma membranes isolated from canine renal cortex, outer and inner medulla in vitro. Though related hormones such as glucagon also stimulate adenylate cyclase in these membrane preparations, it is likely that VIP interacts with specific VIP receptors since the VIP receptor antagonist, (4Cl-D-Phe6, Leu17)-VIP, is capable of reducing the response to VIP, but not that to glucagon. Also binding of 125I-VIP to cortical renal plasma membranes shows competition by unlabelled VIP, but not by glucagon. Strain 1 (and clone CL(8)1b cells derived from the established cultured dog kidney cell line, MDCK, have been shown also to respond selectively to VIP by an increase in adenylate cyclase activity and cyclic AMP accumulation in intact cells. A physiological correlate of VIP activation of adenylate cyclase has been sought by addition of VIP to reconstituted epithelial monolayers of strain 1 MDCK cells clamped in Ussing chambers. VIP addition to the basal-lateral cell aspects generates an inward short-circuit current that is sensitive to replacement of medium Cl- by NO3-, and to inhibition by the Cl- channel blocker, 3-nitro-2(3-phenylpropylamino)-benzoic acid, consistent with VIP stimulation of transepithelial Cl- secretion.
Quarterly Journal of Experimental PhysiologyVolume 74, Issue 2 p. 87-96 ArticleFree Access SPECIAL LECTURE J. J. R. MACLEOD AND THE DISCOVERY OF INSULIN Michael Bliss, Michael Bliss Department of History, University of Toronto, Toronto,Canada M5S JA1Search for more papers by this author Michael Bliss, Michael Bliss Department of History, University of Toronto, Toronto,Canada M5S JA1Search for more papers by this author First published: March 7, 1989 https://doi.org/10.1113/expphysiol.1989.sp003266Citations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume74, Issue2March 7, 1989Pages 87-96 RelatedInformation
A brief account is given of previous work concerned with the effects which ATP (P2-'purinergic') and alpha-adrenaline receptors have on the activity of the sarcoplasmic reticulum (SR) in frog heart atrial cells. More recent experiments made with single atrial trabeculae are also described which suggest, among other things, that ATP and alpha-adrenaline receptors both facilitate the process by which an action potential induces SR calcium discharge in atrial heart cells. The facilitatory effect involved is considerable; at high (greater than or equal to 2 microM) ATP doses, SR calcium discharge seems to be increased about 14-fold and, quite possibly, more than this. Results obtained with different levels of [Ca2+]o during ATP action suggest that the process of calcium-induced calcium release plays little part in the facilitatory process. Its putative mechanism is briefly discussed.
Stimulation of left atrial receptors in dogs anaesthetized with chloralose results in a reflex diuresis and a small decrease in the plasma concentration of vasopressin. It has been suggested that this diuretic response is solely mediated by the antidiuretic hormone, vasopressin (Gauer & Henry, 1976; Ledsome, 1985). The present investigation was designed to determine how these anaesthetized dogs, which are thought to be insensitive to changes in plasma vasopressin, respond to small decreases in plasma vasopressin similar to those observed during stimulation of left atrial receptors. In the event it was shown for the first time that it is possible to obtain a water diuresis in an anaesthetized animal in response to a small fall in the concentration of plasma vasopressin. In order to produce changes in plasma vasopressin similar to those seen during stimulation of left atrial receptors the pituitary gland was removed and an intravenous infusion of arginine vasopressin was given in eleven dogs anaesthetized with chloralose; a small decrease in plasma vasopressin was then produced by replacing the vasopressin with an infusion of saline for 30 min. A decrease in the plasma concentration of 1.29 pg cm-3 from a control concentration of 1.85 pg cm-3 resulted in a 96.7% increase in urine flow. The fall in concentration of vasopressin consequent upon stimulation of atrial receptors could, therefore, explain the water diuresis in the anaesthetized dog preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
Quarterly Journal of Experimental PhysiologyVolume 74, Issue 7 p. 1-2 ArticleFree Access THE SCHOOL OF BERNARD KATZ PREFACE T. J. BISCOE, T. J. BISCOE Department of Physiology, University College London, Gower Street, London WC1E 6BTSearch for more papers by this author T. J. BISCOE, T. J. BISCOE Department of Physiology, University College London, Gower Street, London WC1E 6BTSearch for more papers by this author First published: 07 December 1989 https://doi.org/10.1113/expphysiol.1989.sp003375AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume74, Issue7December 7, 1989Pages 1-2 RelatedInformation
Quarterly Journal of Experimental PhysiologyVolume 74, Issue 6 p. 785-804 ArticleFree Access IONIC CHANNELS: EVOLUTIONARY ORIGINS AND MODERN ROLES Bertil Hille, Bertil Hille Department of Physiology and Biophysics SJ-40, University of Washington Medical School, Seattle, WA 98195, USASearch for more papers by this author Bertil Hille, Bertil Hille Department of Physiology and Biophysics SJ-40, University of Washington Medical School, Seattle, WA 98195, USASearch for more papers by this author First published: 12 November 1989 https://doi.org/10.1113/expphysiol.1989.sp003349Citations: 45AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume74, Issue6November 12, 1989Pages 785-804 RelatedInformation
The effects of insulin on fetal growth rates were investigated by measuring crown-rump length (CRL) chronically in sheep fetuses before and after pancreatectomy, sham operation or pancreatectomy accompanied by insulin-replacement treatment. Pancreatectomy of the fetus produced hypoinsulinaemia and reduced the daily and total increments in CRL by 40-50% over the last 20-30 days of gestation. The growth rate fell immediately after pancreatectomy and remained low throughout the rest of gestation. In contrast to the sham-operated fetus no pre-partum decline in the growth rate was observed in the pancreatectomized animal. The body weight, limb lengths and actual CRL at delivery were also significantly less after pancreatectomy than in the sham-operated animals. When fetal insulin levels were maintained after pancreatectomy by exogenous insulin infusion, the daily and total increments in CRL and the body size at delivery were restored to their normal values. Raising insulin levels above normal in the pancreatectomized fetus did not lead to additional fetal growth. When the data from all the fetuses were combined irrespective of treatment, there were significant positive correlations between the plasma insulin concentration in utero and the mean daily increment in CRL after treatment and between the former value and the body weight at delivery. These observations demonstrate that insulin is a major determinant of the growth rate in utero and that it is required throughout late gestation for the normal growth and development of the sheep fetus. They also indicate that insulin deficiency is probably the primary cause of the growth retardation observed after fetal pancreatectomy.
Cultured myoblasts from Xenopus laevis differentiating in a DC electric field (approximately 100 mV/mm) had more microfilaments, more striated myofibrils and an increased Z-disc diameter than myoblasts in control cultures.
Microelectrodes were inserted at random into superficial fibres in rat regenerating soleus muscles. The fibres from which recordings of electrical properties were made were marked using the dye Lucifer Yellow CH and then processed for histological studies. It was shown that the microelectrodes had sampled small regenerating muscle fibres, and that random penetration does not select for any undamaged fibres that may be present.
