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1.
A. J. Bullock R. A. Duquette N. Buttell S. Wray 《Pflügers Archiv : European journal of physiology》1998,435(4):575-577
Intracellular pH (pHi) is known to modulate contraction. Neonatal tissues can differ from adult tissue in contractile response to stimuli known
to alter pHi e.g. hypoxia. Changes of pH are attenuated by buffering, thus any difference in buffering power (β) between tissues could
affect their functional response to pHi perturbation. Similarly the extent to which any extracellular pH (pHo) alteration is transmitted into a pHi change will also influence function. We have therefore determined the intrinsic β and effect of pHo change on pHi in neonatal and adult ureteric, uterine and gastric smooth muscles using the pH-sensitive fluorophore carboxy-SNARF. β was
found to be similar in the three adult tissues, but there were significant differences between neonatal tissues. In contrast,
we found little difference in the amount of pHi change produced by pHo change between neonatal and adult tissues from the same smooth muscle, but a difference between smooth muscles. These data
highlight significant differences between smooth muscles and their developmental state, which may contribute to different
degrees of protection when pH is perturbed.
Received: 17 October 1997 / Received after revision: 27 November 1997 / Accepted: 28 November 1997 相似文献
2.
Voltage-dependent K+ currents (Kv) may play a role in hypoxic pulmonary vaso constriction. The effects of changes in extracellular pH (pHo) and intracellular pH (pHi) on Kv currents in smooth muscle cells isolated from canine pulmonary artery were studied using the amphotericin B perforated-patch
technique for whole-cell recording. Under these conditions, cellular mechanisms for pHi regulation remain intact, and the effects of pHo were examined by directly changing the pH of external solutions and changes in pHi were produced by external application of weak extracellular acids and bases and the cation/H+ ionophore, nigericin. Ca2+-free external solutions were used to isolate whole-cell Kv currents from contaminating Ca2+-activated K+ currents. Extracellular acidification (pHo = 6.4–7.0) reduced Kv currents, produced a positive voltage shift in steady-state activation and reduced maximum Kv conductance (-g
K). Extracellular alkalinization (pHo = 8.0–8.4) increased Kv currents, produced a small negative voltage shift in steady-state activation, and increased -g
K. Intracellular acidification produced by exposure of cells to external sodium butyrate (20 mM) or nigericin (5 μg/ml) increased
Kv currents, produced a negative voltage shift in steady-state activation, and increased -g
K. Intracellular alkalinization produced by exposure of cells to external trimethylamine (20 mM) reduced Kv currents, produced a small positive voltage shift in steady-state activation and reduced -g
K. These results suggest that the effects of pHo and pHi on Kv currents are distinctly different, but are consistent with reported effects of pHo and pHi on hypoxic pulmonary vasoconstriction, suggesting that such modulation may be mediated in part by pH-induced alterations in
Kv channel activity.
Received: 1 November 1996 / Received after revision: 19 December 1996 / Accepted: 3 January 1997 相似文献
3.
Modulation of HERG potassium channel properties by external pH 总被引:3,自引:0,他引:3
Jocelyn Bérubé Mohamed Chahine P. Daleau 《Pflügers Archiv : European journal of physiology》1999,438(3):419-422
We expressed the human eag-related gene (HERG), known to encode for the cardiac potassium channel IKr, in Chinese hamster ovary (CHO) cells. This study investigated effects of external pH (pHo) on HERG current properties using the whole-cell patch-clamp technique. We observed that current amplitude was decreased
and kinetics of activation and deactivation were faster when pHo was lowered from 7.4 to 6.0, while activation was accelerated and V
1/2 negatively shifted when pHo was changed from 7.4 to 8.0. These effects can be explained by surface charge screening, amino acid group titration and/or
changes in ionic atmosphere. We conclude that alterations of HERG channel by pHo could have consequences for the onset of arrhythmias during cardiac ischemia.
Received: 11 February 1999 / Received after revision: 19 April 1999 / Accepted: 26 April 1999 相似文献
4.
Changes in intracellular pH (pHi) are thought to produce large changes in force production in the uterus. There have however, been no simultaneous measurements of pHi and force in the uterus and therefore no direct information is available about the relation between the two. We have used carboxy-SNARF (a pH-sensitive fluorophore) in small strips of longitudinal myometrium and obtained simultaneous measurements of pHi and force. SNARF did not alter contractile function, and continuous measurements of pHi could be made for 2 hours. The mean resting pHi (7.16) was similar to that reported previously. Application of weak bases rapidly raised pHi, in a concentration-dependent manner, followed by a gradual restoration of pHi to resting levels. Alkalinization greatly increased the frequency of contractions, often accompanied by a small increase in their amplitude. Removal of base produced a rebound acidification which transiently abolished contractions. Direct acidification of the cytoplasm, by application of weak acid, also abolished contractions. However the alkalinization which accompanied removal of acid, produced variable effects on force.Supported by the M.R.C. 相似文献
5.
Precise spatiotemporal regulation of intracellular pH (pHi) is a prerequisite for normal cell function, and changes in pHi or pericellular pH (pHe) exert important signalling functions. It is well established that proliferation of mammalian cells is dependent on a permissive pHi in the slightly alkaline range (7.0‐7.2). It is also clear that mitogen signalling in nominal absence of is associated with an intracellular alkalinization (~0.3 pH unit above steady‐state pHi), which is secondary to activation of Na+/H+ exchange. However, it remains controversial whether this increase in pHi is part of the mitogenic signal cascade leading to cell cycle entry and progression, and whether it is relevant under physiological conditions. Furthermore, essentially all studies of pHi in mammalian cell proliferation have focused on the mitogen‐induced G0‐G1 transition, and the regulation and roles of pHi during the cell cycle remain poorly understood. The aim of this review is to summarize and critically discuss the possible roles of pHi and pHe in cell cycle progression. While the focus is on the mammalian cell cycle, important insights from studies in lower eukaryotes are also discussed. We summarize current evidence of links between cell cycle progression and pHi and discuss possible pHi‐ and pHe sensors and signalling pathways relevant to mammalian proliferation control. The possibility that changes in pHi during cell cycle progression may be an integral part of the checkpoint control machinery is explored. Finally, we discuss the relevance of links between pH and proliferation in the context of the perturbed pH homoeostasis and acidic microenvironment of solid tumours. 相似文献
6.
R. Marrannes A. de Hemptinne I. Leusen 《Pflügers Archiv : European journal of physiology》1981,389(3):199-209
Conduction velocity in isolated rabbit atrial fibers was continuously measured in solutions having a different anionic composition. When 20 mmol/l of chloride was replaced by 20 mmol/l lactate or other anions of weak organic acids at constant pH 6.8, biphasic initial transient changes in conduction velocity were observed. The produced transient changes had a greater amplitude with organic acids which have a greater pK and lipid/water partition ratio. The magnitude of the transients was also greater at pH 6.8 than at pH 7.5, and also when the buffering capacity of the superfusion solution was smaller. Measurements of intracellular pH (pHi) in sheep Purkinje fibers and of pH at the surface (pHs) of sheep Purkinje and rabbit atrial fibers with pH sensitive microelectrodes, showed a transient increase of pHs and a sustained decrease of pHi on replacement of 20 mmol/l chloride by organic anions of weak acids (at constant pH of the superfusion solution). A combined influence of the transient pHs change and the sustained pHi modification seems to be important in the explanation of the biphasic changes in conduction velocity. 相似文献
7.
Alterations in proteolytic activity at low pH and its association with invasion: A theoretical model
The extracellular pH (pHe) of solid tumours is often lower than in normal tissues, with median pH values of about 7.0 in tumours and 7.5 in normal tissue. Despite this more acidic tumour microenvironment, non-invasive measurements of intracellular pH (pHi) have shown that the pHi of solid tumours is neutral or slightly alkaline compared to normal tissue (pHi 7.0–7.4). This gives rise to a reversed cellular pH gradient between tumours and normal tissue, which has been implicated in many aspects of tumour progression. One such area is tumour invasion: the incubation of tumour cells at low pH has been shown to induce more aggressive invasive behaviour in vitro. In this paper the authors use mathematical models to investigate whether altered proteolytic activity at low pH is responsible for the stimulation of a more metastatic phenotype. The authors examined the effect of culture pH on the secretion and activity of two different classes of proteinases: the metalloproteinases (MMPs), and the cysteine proteinases (such as cathepsin B). The modelling suggests that changes in MMP activity at low pH do not have significant effects on invasive behaviour. However, the model predicts that the levels of active-cathepsin B are significantly altered by acidic pH. This result suggests a critical role for the cysteine proteinases in tumour progression. 相似文献
8.
Although intracelluar pH (pHi) is expected to change during inhibition of oxidative phosphorylation and to affect force, there have been no simultaneous measurements of its effect on pHi and force in smooth muscle. Therefore, we have investigated the relationship between force and pHi in strips of longitudinal rat myometrium, loaded with the pH-sensitive indicator carboxy-SNARF and simultaneously measured tension. The application of cyanide produced an abolition of spontaneous contractions and a rapid initial fall in pHi. In 9/19 preparations pHi then started to return to resting values but there was no corresponding restoration of force. Cyanide and weak base were simultaneously added to uterine preparations to prevent any acidification; force still fell. Addition of cyanide to depolarized preparations also produced an acidification and a fall in force. Depolarization of preparations in which spontaneous force had been abolished by cyanide often produced a transient rise in force, despite further acidification of the cytoplasm. Cyanide produced an acidification in zero Ca2+-containing solution, similar to that in the presence of Ca2+ indicating little role for changes in [Ca2+] in producing the acidifiction. It is concluded that cyanide decreases pHi and force in the uterus, but that there is not a simple relationship between the two. 相似文献
9.
V. B. Turovetskii N. B. Porodina A. N. Erin E. M. Molnar G. T. Sukhikh 《Bulletin of experimental biology and medicine》1995,120(6):1239-1243
The intracellular pH (pHi) of mouse peritoneal neutrophils, initially 0.2 U, drops after a 15-min incubation of these cells with a peptide extract
of fetal brain tissue. Treatment with the preparation leads to appreciable changes in the distribution of neutrophils by the
examined parameter. For macrophages, the acidifying effect of the agent and its effect on the pattern of cell distribution
in terms of pH values are far less expressed. The effects of the agent in dilutions 1∶102 and 1∶104 on the mean pHi are virtually the same.
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 120, N
o
12, pp. 626–630, December, 1995
Presented by V. I. Kulakov, Member of the Russian Academy of Medical Sciences 相似文献
10.
Stewart AK Kurschat CE Alper SL 《Pflügers Archiv : European journal of physiology》2007,454(3):373-384
The ubiquitous AE2/SLC4A2 anion exchanger is acutely and independently regulated by intracellular (pHi) and extracellular pH (pHo), whereas the closely related AE1/SLC4A1 of the red cell and renal intercalated cell is relatively pH-insensitive. We have
investigated the contribution of nonconserved charged residues within the C-terminal transmembrane domain (TMD) of AE2 to
regulation by pH through mutation to the corresponding AE1 residues. AE2-mediated Cl−/Cl− exchange was measured as 4,4′-di-isothiocyanatostilbene-2,2′-disulfonic acid-sensitive 36Cl− efflux from Xenopus oocytes by varying pHi at constant pHo, and by varying pHo at near-constant pHi. All mutations of nonconserved charged residues of the AE2 TMD yielded functional protein, but mutations of some conserved
charged residues (R789E, R1056A, R1134C) reduced or abolished function. Individual mutation of AE2 TMD residues R921, F922,
P1077, and R1107 exhibited reduced pHi sensitivity compared to wt AE2, whereas TMD mutants K1153R, R1155K, R1202L displayed enhanced sensitivity to acidic pHi. In addition, pHo sensitivity was significantly acid- shifted when nonconserved AE2 TMD residues E981, K982, and D1075 were individually converted
to the corresponding AE1 residues. These results demonstrate that multiple conserved charged residues are important for basal
transport function of AE2 and that certain nonconserved charged residues of the AE2 TMD are essential for wild-type regulation
of anion exchange by pHi and pHo.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
A. K. Stewart and C. E. Kurschat have contributed equally to this work. 相似文献
11.
Milton L. Pressler 《Pflügers Archiv : European journal of physiology》1988,411(1):69-75
Regulation of intracellular pH (pHi) and the relationship between H+ and Ca2+ may vary during activity. Ion-selective microelectrodes were used to record pHi during action potentials of sheep Purkinje fibres prolonged by low temperature (21°C) and elevated CO2 content. Intracellular pH also was measured during changes in extracellular calcium concentration, [Ca2+]o. Cytosolic alkalinization (peak pHi change, 0.03–0.05) was observed during the long action-potential plateau and transient acidification (0.01–0.02 units) upon repolarization. Potassium-induced depolarization to plateau potentials (i.e. to –15±2 mV) simulated the peak magnitude of the alkalinization. However, compensation for the alkalinization occurred at a faster rate during the action potential (8.9±4.3 nM/min) than during K+ depolarization (1.2±0.5 nM/min). In comparison, the cytoplasm acidified in resting fibres (0.06–0.07 log units) during changes of [Ca2+]o thought to increase intracellular calcium concentration. Alterations of pHi were translated into changes of proton concentration ([H+]i). Ten-to twenty-fold elevation of [Ca2+]o evoked a comparable change in [H+]i (mean increase, 5.7 nM) but oppositely directed from that during the plateau (mean decrease, 8.8 nM). The findings in resting fibres seem consistent with displacement of bound protons by Ca2+. In contrast, the initial change in pHi during the plateau is proposed to be consequent to Ca2+-release from sarcoplasmic reticulum and/or phosphocreatine hydrolysis coupled to ATP regeneration. 相似文献
12.
Rosana A. Bassani José W. M. Bassani Donald M. Bers 《Pflügers Archiv : European journal of physiology》1995,430(4):573-578
In ferret ventricular myocytes the rate of intracellular Ca concentration [Ca]i decline and relaxation is remarkably fast (compared with rabbit and rat) under conditions where both the sarcoplasmic reticulum Ca uptake and Na/Ca exchange are inhibited. Here we explore the possibility that this rapid [Ca]i decline in ferret cells is attributable to the sarcolemmal Ca ATPase by using carboxyeosin (a potent inhibitor of the sarcolemmal Ca-ATPase). We compare the effects of carboxyeosin with those of elevated extracellular [Ca] ([Ca]o) (a thermodynamic approach to limit Ca transport by the sarcolemmal Ca ATPase). In rabbit cells, carboxyeosin and high [Ca]o slowed [Ca]i decline similarly and both virtually abolished [Ca]i decline when mitochondrial Ca uptake was also inhibited. In ferret cells, carboxyeosin treatment produced these same effects on [Ca]i decline, but high [Ca]o did not mimic them. Moreover, only in carboxyeosintreated ferret cells did additional inhibition of mitochondrial Ca uptake nearly abolish [Ca]i decline. We conclude that, carboxyeosin loading can inhibit the sarcolemmal Ca-ATPase in intact myocytes; that this pump seems likely to be responsible for the much faster relaxation observed in ferret cells after block of SR Ca accumulation and Na/Ca exchange transport and that the sarcolemmal Ca pump apparently has different characteristics in rabbit and ferret ventricular myocytes.
Present address: Centro de Engenharia Biomédica Caixa Postal 6040, Universidade Estadual de Campinas (UNICAMP), 13081 Campinas, SP, Brazil 相似文献
13.
N. A. Curtin 《Journal of muscle research and cell motility》1990,11(3):251-257
Summary The force—velocity relation of frog sartorius muscle was observed during slow stretch and during shortening in solutions with and without CO2 at extracellular pH (pHo) 6.9 and pHo 7.5 (5° C). Less force was produced with CO2 than without CO2 during stretch, during shortening, and under isometric conditions. Compared with pHo 7.5, the effects were greater at pHo 6.9, where the concentration of CO2, a permeant acid, was greater and would cause a greater acidification of intracellular pH (pHi). The reduction of force caused by CO2 was smaller during stretch than during shortening or isometric contraction. This result indicates that the crossbridge states specific to stretch retain their ability to produce force better under acidic conditions than those characteristic of shortening and isometric conditions. This difference between stretch and shortening suggests that there may be compensating changes in the pattern of motor unit activity during fatiguein vivo. 相似文献
14.
Intracellular pH (pHi) plays a critical role in the physiological processes of cells. Nanoscale sensors based on pH-sensitive fluorescent proteins attached on nanoparticles (NPs) have been designed but inorganic NP-dependent fluorescent nanosensors have not yet been explored. Herein we describe a pH sensitive inorganic semiconductor fluorescent probe based on ultrathin 3C–SiC NPs which can effectively monitor pH in the range of 5.6–7.4 by taking advantage of the linear dependence between the fluorescent intensity ratio of the surface OH− and H+ bonding states to band-to-band recombination and pH. Detection of pHi is demonstrated in living HeLa cells. In particular, pHi measurements during apoptosis confirm the validity and sensitivity of this technique in monitoring real-time changes in the intracellular environment. Toxicity assessment and confocal laser scanning microscopy indicate that the 3C–SiC NPs have low cytotoxicity and are compatible with living cells. 相似文献
15.
In isolated sheep cardiac Purkinje strands the effect of membrane depolarization on intracellular pH (pHi) and on pHi changes produced by addition and withdrawal of NH
4
+
and CO2/HCO
3
–
was investigated. pHi was continuously measured with double-barreled glass microelectrodes. Repetitive stimulation at high rate resulted in a moderate intracellular acidification (approximately 0.03 pH unit after a 3 Hz train of 2 min), whereafter pHi returned toward its pre-stimulus level. Prolonged depolarization, evoked either by current injection or by superfusion with high K+ solutions, was accompanied by a small acid shift. In the depolarized cell, addition of NH
4
+
to the superfusate caused intracellular alkalinization followed by re-acidification which was slower than at normal membrane potential. Following intracellular acidification caused by withdrawal of NH
4
+
, pHi recovery also was slightly slower than in the normally polarized cell. In the depolarized fiber, removal and readdition of CO2/HCO
3
–
produced the expected intracellular alkalinization and acidification respectively. Recovery from CO2-induced acidosis was slowed somewhat in high K+ (low Na+) superfused fibers, not in current depolarized fibers. In the depolarized cell, steady state pHi in CO2/HCO
3
–
containing and in CO2/HCO
3
–
free solution tended to become identical. These experiments support the hypothesis that in the normally polarized Purkinje fiber passive shuttle movement of NH
4
+
/NH3 and CO2/HCO
3
–
occurs and could perhaps at least be partly responsible for the lower steady state pHi as compared to that reached in NH
4
+
-free and CO2/HCO
3
–
-free solutions respectively. 相似文献
16.
Pantazis A Keegan P Postma M Schwiening CJ 《Pflügers Archiv : European journal of physiology》2006,452(2):175-187
Neuronal depolarization causes larger intracellular pH (pHi) shifts in axonal and dendritic regions than in the cell body. In this paper, we present evidence relating the time for collapse of these gradients to neuronal morphology. We have used ratiometric pHi measurements using 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) in whole-cell patch-clamped snail neurons to study the collapse of longitudinal pH gradients. Using depolarization to open voltage-gated proton channels, we produced alkaline pHi microdomains. In the absence of added mobile buffers, facilitated H+ diffusion down the length of the axon plays a critical role in determining pHi microdomain lifetime, with axons of ∼100 μm allowing pH differences to be maintained for >60 s. An application of mobile, membrane-permeant pH buffers accelerated the collapse of the alkaline-pH gradients but, even at 30 mM, was unable to abolish them. Modeling of the pHi dynamics showed that both the relatively weak effect of the weak acid/base on the peak size of the pH gradient and the accelerated collapse of the pH gradient could be due to the time taken for equilibration of the weak acid and base across the cell. We propose that appropriate weak acid/base mixes may provide a simple method for studying the role of local pHi signals without perturbing steady-state pHi. Furthermore, an extrapolation of our in vitro data to longer and thinner neuronal structures found in the mammalian nervous system suggests that dendritic and axonal pHi are likely to be dominated by local pHi-regulating mechanisms rather than simply following the soma pHi. 相似文献
17.
Kotaro Kaneko Paul H. Guth Jonathan D. Kaunitz 《Pflügers Archiv : European journal of physiology》1992,421(4):322-328
Intracellular pH (pHi) and viability of gastric surface cells of the rat stomach in response to luminal acidification, and the role of Na+/H+ exchange in maintaining pHi homeostasis were studied in vivo using a fluorescent microscopic technique. pHi was measured during superfusion with buffers of pH 1.2–7.4. When the pH of the superfusate was 7.4, baseline pHi was unchanged. Superfusion with pH 3 buffer rapidly decreased pHi to 6.7, with subsequent recovery to baseline pHi within 15 min despite continuing acid exposure. Superfusion with buffers of pH 1.7 and 1.2 decreased pHi continuously to below 6.2 with no recovery observed. Despite the relentless decline in pHi during superfusion with pH-1.2 and –1.7 solutions, over 75% of the surface cells were still viable, as measured by exclusion of the vital dye propidium iodide. We then examined the role of Na+/H+ exchange in the regulation of pHi. Superfusion with amiloride did not affect recovery of pHi from intracellular acidification induced by a NH4Cl prepulse. Exposure to the potent, lipophilic Na+/H+ exchange inhibitor 5-(N,N-hexaniethylene)-amiloride (HMA), either in the superfusate or by close arterial perfusion, decreased baseline pHi from 7.1 to 6.8. Close arterial perfusion of HMA additionally attenuated the recovery of pHi to baseline during superfusion with pH 3 buffer. We conclude that luminal protons permeate into the cytoplasm of gastric surface cells, where they are eliminated by an Na+/H+ exchanger, most probably localized to the basolateral membrane. 相似文献
18.
D. Hoppe H. -D. Lux M. Schachner H. Kettenmann 《Pflügers Archiv : European journal of physiology》1989,415(1):22-28
We analyzed the pH dependence of K+ currents recorded with the patch-clamp technique from cultured Schwann cells obtained from mouse dorsal root ganglia. Currents were activated at potentials more positive than ?50 mV which was close to the resting membrane potential. Current amplitudes were affected by a change in extracellular pH (pHo), being increased at alkaline, and decreased at acidic pHo. The strongest effect of a pHo change was observed on currents activated close to the resting membrane potential suggesting a functional role for the pH sensitivity of K+ currents. Analysis of the time course of current activation at different pHo values led to the conclusion that the pH-sensitivity of K+ currents in Schwann cells is due to changes in surface charges shifting the potential sensed by the gating process of the channel. The reversal potential of the currents was not affected by a change in pHo. This observation and the finding that even a strong acidification to a pHo value of 5.0 did not lead to a blockade of the fully activated channel, indicate that the pH-sensitive charges are not located in the channel pore. Under the assumption that pHo changes in a peripheral nerve are associated with nerve activity as in the optic nerve, the pH-sensitive K+ channel in Schwann cells could serve to facilitate the spatial buffering of extracellular K+. 相似文献
19.
D. Hoppe H. -D. Lux M. Schachner H. Kettenmann 《Pflügers Archiv : European journal of physiology》1990,415(1):22-28
We analyzed the pH dependence of K+ currents recorded with the patch-clamp technique from cultured Schwann cells obtained from mouse dorsal root ganglia. Currents were activated at potentials more positive than –50 mV which was close to the resting membrane potential. Current amplitudes were affected by a change in extracellular pH (pHo), being increased at alkaline, and decreased at acidic pHo. The strongest effect of a pHo change was observed on currents activated close to the resting membrane potential suggesting a functional role for the pH sensitivity of K+ currents. Analysis of the time course of current activation at different pHo values led to the conclusion that the pH-sensitivity of K+ currents in Schwann cells is due to changes in surface charges shifting the potential sensed by the gating process of the channel. The reversal potential of the currents was not affected by a change in pHo. This observation and the finding that even a strong acidification to a pHo value of 5.0 did not lead to a blockade of the fully activated channel, indicate that the pH-sensitive charges are not located in the channel pore. Under the assumption that pHo changes in a peripheral nerve are associated with nerve activity as in the optic nerve, the pH-sensitive K+ channel in Schwann cells could serve to facilitate the spatial buffering of extracellular K+. 相似文献
20.
Strips of rat mesenteric artery were loaded with carboxy-seminaphthorhodafluor (SNARF) to measure intracellular pH (pHi) and force simultaneously. pHi was altered by using weak acids and bases. Alkalinization produced an increase in force. For equal elevations of pHi a greater and faster increase of force was obtained in depolarized (high K+) than in non-depolarised preparations. Acidification produced little change in force unless the tissue was contracted (high-K+), in which case it elicited relaxation. Examination of the relationship between pHi and force in depolarized preparations showed that acidification produced a greater change in force than alkalinization. Removal
of weak bases produced a transient acidification that was accompanied by a fall in force in all preparations. This was followed
by a secondary contraction in depolarized preparations during the period over which pHi was acidic and being restored to resting values. Some preparations demonstrated a hysteresis in the relation between pHi and force. It is concluded that the relationship between pHi and force in mesenteric vascular smooth muscle is not constant but depends on the previous history of the preparation, and
may involve differences in the interactions between H+, Ca2+ and the contractile machinery. 相似文献