Regulation of cytosolic Ca2+ in resting and stimulated rat submandibular salivary gland acini.

To determine the range over which cytosolic Ca2+ concentration (Cai2+) is regulated, Cai2+ was measured in salivary acini loaded with Fura-2. With extracellular Ca2+ (Cao2+) = 2.5 mM, mean resting Cai2+ (+/- SD) was 103 +/- 20 nM (n = 29). Carbachol increased Cai2+ immediately to 288 +/- 81 nM, which then declined to a sustained level of 253 +/- 58 nM. When Cao2+ was less than 10 nM, the immediate response to carbachol was little affected but the sustained response was abolished. Atropine abolished all responses to carbachol. Changes in Cai2+ were not due to Ca2+-induced Ca2+ release or to Ca2+ influx via voltage-dependent channels. With Cao2+ = 2.5 mM, epinephrine raised Cai2+ initially to 196 +/- 57 nM (n = 6), which soon declined to stable levels of 178 +/- 40 nM. When Cao2+ was less than 10 nM the prolonged response to epinephrine was abolished but the initial increase was relatively unaffected. All epinephrine-induced changes in Cai2+ were abolished by prazosin. The range of Cai2+ measured corresponds to that over which non-mitochondrial Ca2+ transport is stimulated in permeabilized submandibular gland acini suggesting that such a Ca2+ transport system may regulate physiological changes in Cai2+ in these acini in the rat.