Effect of temperature on intracellular pH in crayfish neurons and muscle fibers

Effect of temperature on pH and electrolyte concentration in air-breathing ectotherms

The aim of this study was to determine the effects of temperature upon pH, protein charge and acid-base-relevant ion exchange in air-breathing ectotherms. Plasma and skeletal muscles in cane toads (Bufo marinus) and bullfrogs (Rana catesbeiana) were examined at 30, 20 and 10 degrees C. In addition, skeletal muscle ion concentrations were examined in black racer snakes (Coluber constrictor) at 30 and 10 degrees C. Cooling the amphibians produced a reduction in most of the plasma ion concentrations (Na(+), K(+), Ca(2+), Cl(−), SO(4)(2)(−)) and in protein concentration because of increased hydration. Between 30 and 10 degrees C, total plasma osmolality fell by 14 % in the toads and by 5 % in the frogs. Plasma protein charge, calculated using the principle of electroneutrality, was unaffected by temperature, except possibly for the toads at 10 degrees C. The in vivo skeletal muscle capdelta pHi/ capdelta T ratio, where pHi is intracellular pH and T is temperature, between 30 and 20 degrees C averaged −0.014 degrees C(−)(1) in the toads and −0.019 degrees C(−)(1) in the frogs. Between 20 and 10 degrees C, there was no change in pHi in the toads and a −0.005 degrees C(−)(1) change in the frogs. The in vitro skeletal muscle capdelta pHi/ capdelta T averaged −0.011 degrees C(−)(1) in both toads and frogs. In all three species, skeletal muscle inulin space declined with cooling. Intracellular ion concentrations were calculated by subtracting extracellular fluid ion concentrations from whole-muscle ion concentrations. In general, temperature had a large effect upon intracellular ion concentrations (Na(+), K(+), Cl(−)) and intracellular CO(2) levels. The relevance of the changes in intracellular ion concentration to skeletal muscle acid-base status and protein charge and the possible mechanisms producing the adjustments in intracellular ion concentration are discussed. It is concluded that ion-exchange mechanisms make an important contribution to adjusting pH with changes in temperature.

Buffer capacity of rat cortical tissue as well as of cultured neurons and astrocytes

The primary objective of this work was to assess the intrinsic nonbicarbonate buffer capacity (beta i) of cultured neurons and astrocytes and to compare the beta i values obtained to those of neocortical tissue. A second objective was to determine the pH dependence of beta i. Titration of homogenates of whole-brain cortical tissue and cultured neurons with NaOH and HCl gave beta i values of 25-30 mmol.l-1 x pH-1. The buffer capacity was essentially constant in the pH range of 6-7. Astrocytes showed a higher buffer capacity and a clear relationship between beta i and pH. However, beta i decreased when pH was reduced from 7 to 6. The beta i values derived from microspectrofluorometric studies on neurons and astrocytes were surprisingly variable, ranging from 10 to 50 mmol.l-1 x pH-1. The ammonia "step method" suggested that beta i increased dramatically when pH was lowered from 7 to 6 but the propionic "step method" failed to reveal such a pH dependence. Some techniques obviously give erroneous values for beta i, presumably because changes in buffer base concentration (due to transmembrane fluxes of H+, HCO3-, NH4+ or anions of weak acids) violate the principles upon which the calculations are based. From the results obtained by direct titration and with the propionate technique, we tentatively conclude that beta i in neurons and astrocytes are approximately 20 and 30 mmol.l-1 x pH-1, respectively. We further suggest that the term "intrinsic buffer capacity", as commonly used, is redefined.

Ultrastructural study of cytochemical localization of carbonic anhydrase in the inner ear

Vibratome sections were stained for cytochemical localization of carbonic anhydrase (CA) activity in vestibular neuro-epithelium, spiral ligament and spiral limbus. The new finding is the localization of reaction products in the interdental cells of the spiral limbus, Claudius' cells, mesothelial cells of the lower border of spiral ligament, vestibular sensory cells and perilymphatic cells, which have not earlier been proved to have CA activity. The interdental cells showed the products only on the basolateral infoldings. Claudius' cells showed prominent products in the microvilli. In the vestibular sensory cells, the products were present only in the stereocilia and cuticular areas. The perilymphatic fibrocytes under the vestibular sensory epithelium, like the fibrocytes of the spiral ligament, revealed diffuse products throughout the whole cell. In the vestibular supporting cells and transitional cells, the reaction products were localized diffusely in the cytosol, but not in the secretory granules. In the long cell projections of the transitional cells, type II fibrocytes at spiral prominence, mesothelial cells at the uppermost region of the spiral ligament and Borghesan's zone, the localization of the reaction products was the same as that of the basolateral infoldings of the vestibular dark cells and marginal cells of stria vascularis shown previously.

The intrinsic intracellular H+ buffering power of snail neurones

1. We measured intracellular pH (pHi) in snail neurones using pH-sensitive glass microelectrodes. We then calculated the intracellular buffering power (beta i) from the pHi changes associated with the influx or efflux of a variety of weak acids or bases. 2. The weak acid anions butyrate and propionate (20 mM) gave similar values for beta i but those measured using 20 mM-acetate were on average twice as great. 3. Although solutions were nominally CO2-free, blockage of pHi regulation with SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) increased the sizes of the pHi changes upon weak acid addition and removal. The corresponding measured values of beta i were on average 26% lower with SITS than without. 4. With pHi regulation blocked, the use of 2.7% CO2 to measure beta i gave beta i values similar to those measured with butyrate or propionate. These values were about 50% less than those previously measured in snail neurones using CO2. 5. beta i values calculated from the pHi changes due to the removal of 5 mM of the weak bases trimethylamine, procaine and NH4Cl were all similar and comparable to those measured using butyrate or propionate. Removing the influence of pHi regulation on the undershoots after NH4Cl removal was found to decrease the apparent measured values of beta i by 10%. 6. Combining all the data (except the values obtained using CO2 and acetate), and adjusting for the errors due to pHi regulation reducing the sizes of the pHi changes, we found that the mean value for beta i was 10.4 +/- 0.6 mM (+/- S.E.M.) at a mean pHi of 7.36 +/- 0.05. 7. We also investigated the relationship between beta i and pHi using ionophoretic acid injection. By means of step-wise injections, with pHi regulation blocked, we found that at normal pHi levels beta i remained relatively constant. However, at a pHi of less than about 6.8 beta i increased with decreasing pHi.

Phasic changes in intracellular pH during action potentials of sheep Purkinje fibres

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 degrees 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.

The ionic mechanism of intracellular pH regulation in crayfish muscle fibres

The ionic mechanism of intracellular pH (pHi) regulation was investigated in isolated muscle fibres of the carpopodite adductor in the crayfish Astacus fluviatilis by electrophysiological means with pH, Na+ and Cl- -sensitive liquid ion exchanger micro-electrodes. In eighty-six cells a mean pHi of 7.14 +/- 0.12 (S.D.) at a membrane potential of--79.7 +/- 3.4 mV was found under control conditions which is about one pH unit more alkaline than predicted from passive distribution and indicates the presence of an acid-extrusion mechanism. In order to study pHi recovery the cells were acid loaded by exposure either to NH4 Cl or CO2. The effects of HCO3- and DIDS (an inhibitor of the anion exchange) on pHi recovery as well as the HCO3- -dependent decrease of intracellular Cl- during pHi recovery indicate that in pHi regulation a mechanism of acid extrusion is involved which exchanges extracellular HCO3- for intracellular Cl-. In CO2/HCO3- -free solution or in salines with DIDS, pHi recovery was retarded to the same degree, but the effects were not additive. Because of this the remaining pHi recovery must originate from an HCO3- -independent acid-extrusion mechanism. In Na+ -free solution any pHi recovery was blocked; if pHi recovery occurred it was accompanied by an increase of intracellular Na+ activity (aiNa). From these results it was concluded that all acid extrusion mechanisms which contributed to pHi recovery are coupled to an influx of Na+. A Na+/H+/HCO3-/Cl-, and a separate Na+/H+, exchange are proposed as a model of pHi regulation in the crayfish muscle fibre. Similar kinds of acid extrusion mechanisms are found in the neurone of the crayfish (Moody, 1981), with the difference that in the muscle fibre pHi regulation is achieved mainly by the former process. The rate of pHi recovery is considerably lower in the muscle fibre than in the neurone or in the sensory cell (Moser, 1985) of crayfish.

Intracellular pH in hibernation and respiratory acidosis in the European hamster

Intracellular pH was determined (DMO method) in European hamsters, in the spontaneously-occurring respiratory acidosis of hibernation, in hypercapnia due to breathing 12% CO2 in air in euthermy in spring, and in euthermicnormocapnic controls. From euthermy to hibernation, the temperature coefficient of pH was lowest in blood plasma and brain, intermediate in striated muscles (thigh muscles and diaphragm), and highest in heart and liver (Fig. 1). Correspondingly, the estimated dissociation ratio of the protein imidazole buffer groups, alpha Im, decreased markedly in plasma and brain, denoting an acid titration, but varied little in liver and heart. Striated muscles were intermediate (Fig. 2). Like in other mammals, intracellular responses to short-term euthermic respiratory acidosis were characterized by a partial metabolic compensation in the brain and a small metabolic acidification in striated muscles. In hibernation, a powerful metabolic compensation took place in liver and heart, nearly restoring alpha Im, but none occurred in brain (Figs. 3 to 5). The existence of an intracellular acidosis in brain and striated muscles during hibernation is in keeping with an inhibitory role of acidosis, whereas the homeostasis of intracellular alpha Im in liver and heart would subserve the eurythermal functioning of metabolic regulations in these organs, like in most organs of ectotherms.