Modulation Of Intracellular pH Research Articles

Does modulation of intracellular pH during early reperfusion influence vulnerability to reperfusion arrhythmias?

Does modulation of intracellular pH during early reperfusion influence vulnerability to reperfusion arrhythmias?

Modulation of intracellular pH by secretagogues and the Na +/H + antiporter in cultured bovine chromaffin cells

The possible physiological role of cytosolic pH changes in adrenal medullary chromaffin cell secretion was examined by investigating the effects of catecholamine secretagogues on cytosolic pH, which was monitored using the intracellular fluorescent indicator 2′,7′-bis-(2-car☐yethyl)-5(6)-car☐yfluorescein (BCECF). Anti-fluorescein antibodies were used to reduce background fluorescence from extracellular 2′,7′-bis-(2-car☐yethyl)-5(6)-car☐yfluorescein (BCECF). Stimulation with both cholinergic agonists (acetylcholine, nicotine) and a depolarizing agent (high K +) transiently acidified the cytosol of the chromaffin cell. This acidification was antagonized by reducing extracellular Ca 2+ concentration and by Ca 2+ antagonists (Co 2+, verapamil), indicating that it occurred secondarily to Ca 2+ influx, possibly as a result of exchange of Ca 2+ ions for protons across organelle membranes. Taken together with previously published data [Kuijpers G.A.J. et al. (1989) J. biol. Chem. 264, 698–705] showing no effect of cytosolic acidification on nicotine-induced catecholamine secretion, these results indicate that secretagogue-induced cytosolic pH changes do not represent a causal step in stimulus-secretion coupling of the chromaffin cell. The cytosolic pH recovery to pre-stimulatory cytosolic pH levels was delayed by amiloride and by5-(N,N-dimethyl)amiloride, at concentrations that otherwise substantially inhibited cytosolic pH recovery from the rebound acidification induced by a 40-fold sudden dilution of NH 4Cl. This latter type of recovery results from activation of an Na +/H + exchange mechanism. Therefore, the data suggest that Na +/H + exchange is actively involved in the dissipation of the small acid loads generated by secretagogues.

Effects of osmotic stresses on isolated rat hepatocytes. II. Modulation of intracellular pH

To assess the roles of acid-base transport systems in cell volume regulation in rat hepatocytes, intracellular pH (pHi) was measured in subconfluent monolayers loaded with 2'-7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) after exposure to hypotonic and relative hypertonic media, interventions that stimulate regulatory volume decrease (RVD) and increase (RVI), respectively. During RVD, pHi decreased from 6.98 +/- 0.11 to 6.85 +/- 0.08 in the absence of HCO3- and from 7.26 +/- 0.10 to 7.19 +/- 0.06 in its presence. Omission of Na+ or addition of 1 mM amiloride prevented the decline in pHi. Acute withdrawal or replacement of Na+ in hypotonic medium resulted in a slower rate of fall or recovery in pHi, respectively, than when the same maneuvers were carried out in isotonic medium. In contrast, during RVI, pHi increased from 6.86 +/- 0.11 to 7.15 +/- 0.15 in the absence of HCO3-, a rise in pHi that was also completely abolished by Na+ removal or by 1 mM amiloride. In the presence of HCO3-, the rise in pHi was less marked than in its absence, although net acid efflux was greater because of a greater intracellular buffering capacity. Cl- removal in the presence of HCO3- had no effect on the change in pHi during either RVD or RVI. Perfusion with 0.5 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) during RVD lowered pHi further and accentuated the subsequent pHi rise seen after the return to isotonic medium. These data suggest that Na(+)-H+ exchange in rat hepatocytes is downregulated during RVD and activated during RVI. Cl(-)-HCO3- exchange does not appear to be involved in hepatocyte volume regulation.

Intracellular pH of astrocytes increases rapidly with cortical stimulation.

Modulation of intracellular pH is widely implicated in the control of cell growth and metabolism, yet little is known about intracellular pH and brain function. To determine how stimulation of brain may affect the intracellular pH of mammalian glial cells, rat cortical astrocytes were studied for the first time in vivo using pH-sensitive electrodes of submicron caliber. Stimulation of the cortical surface caused a cytoplasmic alkaline shift of tenths of a pH within seconds. Cessation of induced electrical activity was followed by pH recovery and a small acid rebound. Recordings obtained during cortical-spreading depression revealed similar but generally larger intracellular pH shifts. Production of metabolic acids is known to occur when the brain is stimulated and has led to the long-held presumption that brain cells accordingly become more acidic. The observation that glia initially become more alkaline during electrical activity is thus paradoxical. The correlation of glial alkalinization with evoked electrical activity suggests that modulation of intracellular pH of glia may have important functional implications.