Modulation of calcium signals by intracellular pH in isolated rat pancreatic acinar cells
T Speake, AC Elliott - The Journal of physiology, 1998 - Wiley Online Library
T Speake, AC Elliott
The Journal of physiology, 1998•Wiley Online Library1 We have investigated the interactions between intracellular pH (pHi) and the intracellular
free calcium concentration ([Ca2+] i) in isolated rat pancreatic acinar cells. The fluorescent
dyes fura‐2 and BCECF were used to measure [Ca2+] i and pHi, respectively. 2 Sodium
acetate and ammonium chloride (NH4Cl) were used to acidify and alkalinize pHi,
respectively. Cytosolic acidification had no effect on [Ca2+] i in resting pancreatic acinar
cells, whereas cytosolic alkalinization released Ca2+ from intracellular stores. 3 Cytosolic …
free calcium concentration ([Ca2+] i) in isolated rat pancreatic acinar cells. The fluorescent
dyes fura‐2 and BCECF were used to measure [Ca2+] i and pHi, respectively. 2 Sodium
acetate and ammonium chloride (NH4Cl) were used to acidify and alkalinize pHi,
respectively. Cytosolic acidification had no effect on [Ca2+] i in resting pancreatic acinar
cells, whereas cytosolic alkalinization released Ca2+ from intracellular stores. 3 Cytosolic …
- 1We have investigated the interactions between intracellular pH (pHi) and the intracellular free calcium concentration ([Ca2+]i) in isolated rat pancreatic acinar cells. The fluorescent dyes fura‐2 and BCECF were used to measure [Ca2+]i and pHi, respectively.
- 2Sodium acetate and ammonium chloride (NH4Cl) were used to acidify and alkalinize pHi, respectively. Cytosolic acidification had no effect on [Ca2+]i in resting pancreatic acinar cells, whereas cytosolic alkalinization released Ca2+ from intracellular stores.
- 3Cytosolic acidification using either acetate or a CO2‐HCO3−‐buffered medium enhanced Ca2+ signals evoked by acetylcholine (ACh) and cholecystokinin (CCK). In contrast, both NH4Cl and trimethylamine (TMA) inhibited Ca2+ signals during stimulation with either ACh or CCK. This inhibitory effect was also observed in the absence of extracellular Ca2+, and was therefore not due to changes in Ca2+ entry.
- 4Calcium oscillations evoked by physiological concentrations of CCK were enhanced by cytosolic acidification and inhibited by cytosolic alkalinization.
- 5In order to determine the effects of pHi upon Ca2+ handling by intracellular Ca2+ stores, intraorganellar [Ca2+] was monitored using the low affinity Ca2+ indicator mag‐fura‐2 in permeabilized cells. Addition of NH4Cl, which is expected to alkalinize intraorganellar pH, did not alter intraorganellar [Ca2+] in permeabilized cells, suggesting that changing intraorganellar pH does not release Ca2+ from intracellular stores. Addition of NH4Cl or acetate also did not affect the rate of Ca2+ release induced by inositol 1,4,5‐trisphosphate (InsP3).
- 6Modification of extraorganellar (‘cytosolic’) pH did not affect the rate of ATP‐dependent Ca2+ uptake into stores, but did modify the rate of Ca2+ release evoked by submaximal concentrations of InsP3. The rate of Ca2+ release was increased at more alkaline extraorganellar pHs. These results would suggest that manipulation of intraorganellar pH does not affect Ca2+ handling by the intracellular stores. In contrast, extraorganellar (‘cytosolic’) pH does affect InsP3‐induced Ca2+ release from the stores.
- 7In conclusion, changes in intracellular pH in pancreatic acinar cells can profoundly alter cytosolic [Ca2+]. This may shed light on earlier observations whereby cell‐permeant weak acids and bases can modulate fluid secretion in epithelia.
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