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Modulation of calcium signals by intracellular pH in isolated rat pancreatic acinar cells
Author(s) -
Speake Tracey,
Elliott Austin C.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.415bw.x
Subject(s) - intracellular , extracellular , cytosol , fura 2 , intracellular ph , calcium , biophysics , chemistry , cholecystokinin , acetylcholine , inositol , biochemistry , calcium in biology , stimulation , biology , endocrinology , receptor , enzyme , organic chemistry
1 We have investigated the interactions between intracellular pH (pH i ) and the intracellular free calcium concentration ([Ca 2+ ] i ) in isolated rat pancreatic acinar cells. The fluorescent dyes fura‐2 and BCECF were used to measure [Ca 2+ ] i and pH i , respectively. 2 Sodium acetate and ammonium chloride (NH 4 Cl) were used to acidify and alkalinize pH i , respectively. Cytosolic acidification had no effect on [Ca 2+ ] i in resting pancreatic acinar cells, whereas cytosolic alkalinization released Ca 2+ from intracellular stores. 3 Cytosolic acidification using either acetate or a CO 2 ‐HCO 3 − ‐buffered medium enhanced Ca 2+ signals evoked by acetylcholine (ACh) and cholecystokinin (CCK). In contrast, both NH 4 Cl and trimethylamine (TMA) inhibited Ca 2+ signals during stimulation with either ACh or CCK. This inhibitory effect was also observed in the absence of extracellular Ca 2+ , and was therefore not due to changes in Ca 2+ entry. 4 Calcium oscillations evoked by physiological concentrations of CCK were enhanced by cytosolic acidification and inhibited by cytosolic alkalinization. 5 In order to determine the effects of pH i upon Ca 2+ handling by intracellular Ca 2+ stores, intraorganellar [Ca 2+ ] was monitored using the low affinity Ca 2+ indicator mag‐fura‐2 in permeabilized cells. Addition of NH 4 Cl, which is expected to alkalinize intraorganellar pH, did not alter intraorganellar [Ca 2+ ] in permeabilized cells, suggesting that changing intraorganellar pH does not release Ca 2+ from intracellular stores. Addition of NH 4 Cl or acetate also did not affect the rate of Ca 2+ release induced by inositol 1,4,5‐trisphosphate (Ins P 3 ). 6 Modification of extraorganellar (‘cytosolic’) pH did not affect the rate of ATP‐dependent Ca 2+ uptake into stores, but did modify the rate of Ca 2+ release evoked by submaximal concentrations of Ins P 3 . The rate of Ca 2+ release was increased at more alkaline extraorganellar pHs. These results would suggest that manipulation of intraorganellar pH does not affect Ca 2+ handling by the intracellular stores. In contrast, extraorganellar (‘cytosolic’) pH does affect Ins P 3 ‐induced Ca 2+ release from the stores. 7 In conclusion, changes in intracellular pH in pancreatic acinar cells can profoundly alter cytosolic [Ca 2+ ]. This may shed light on earlier observations whereby cell‐permeant weak acids and bases can modulate fluid secretion in epithelia.