Modulation of agonist-activated calcium influx by extracellular pH in rat pancreatic acini.
The biochemical and Ca2+ transport pathways involved in generating the hormone-evoked Ca2+ signal are reported to be influenced by pH. The present study was designed to determine the effect of extracellular pH (pHo) and intracellular pH (pHi) on hormone-stimulated Ca2+ transport. We used rat pancreatic acini and measured free cytosolic Ca2+ concentration ([Ca2+]i) with fura-2, pHi with 2,7-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), and Ca2+ fluxes with 45Ca2+. In the presence of external Ca2+, increasing pHo increased steady-state [Ca2+]i during sustained agonist stimulation; in the absence of external Ca2+, this increase in [Ca2+]i did not occur. The addition of an antagonist or blocking plasma membrane Ca2+ influx with La3+ in stimulated cells suspended at pHo 8.2 resulted in a reduction in [Ca2+]i. Increasing pHo increased the rate and extent of 45Ca2+ uptake into stimulated cells and the rate and extent of Ca2+ reloading of intracellular stores. The increased Ca2+ content of the intracellular stores with increased pHo indicated that at physiological pHo and pHi the agonist-mobilizable internal stores are not saturated with Ca2+. Changes in pHo affected pHi. However, changes in pHi at constant pHo had no effect on hormone-evoked [Ca2+]i increase, reduction in [Ca2+]i after hormone stimulation, or reloading of intracellular stores. We conclude that the hormone-activated plasma membrane Ca2+ entry pathway responsible for Ca2+ reloading is directly modulated by external H+.
Muallem
S
S
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235.
Pandol
S J
SJ
Beeker
T G
TG
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology; D019342:Acetic Acid; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000643:Ammonium Chloride / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D002217:Carbachol / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012844:Sincalide / Q000494:pharmacology
D000085:Acetates; D002132:Calcium Radioisotopes; D000643:Ammonium Chloride; C028521:lanthanum chloride; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C039465:5-dimethylamiloride; D007811:Lanthanum; D001285:Atropine; D000584:Amiloride; D002217:Carbachol; D012844:Sincalide; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D019342:Acetic Acid; D002118:Calcium