Involvement of intracellular calcium ions in the release of the fluorescent dye calcein by cholinergic and alpha-adrenergic agonists from rat parotid acinar cells.

Abstract

Effects of cholinergic and adrenergic agonists on the secretion of the fluorescent dye calcein were examined to clarify the involvement of calcium ions in the secretion of calcein from acinar cells dispersed from the rat parotid gland. Addition of carbachol (CCh) and noradrenalin (NA), but not isoproterenol (IPR), enhanced the net release of calcein from acinar cells during the subsequent 10 min in a dose range from 10(-8) M to 10(-6) M. The net release of calcein reached a maximum 7 min after the addition of CCh. The release of calcein was suppressed by the simultaneous additions of atropine with CCh, or phenoxybenzamine with NA. Addition of CCh induced a sustained dose-dependent increase in the intracellular levels of calcium ions, ([Ca2+]i). Addition of NA at 10(-6) M increased [Ca2+]i. Phenoxybenzamine completely inhibited the NA-induced increase, but propranolol did not. The removal of extracellular calcium ions did not influence the release of calcein induced by 10(-6) M CCh, but it abolished the sustained increase in [Ca2+]i. The transient increase in [Ca2+]i induced by CCh was observed in the absence of extracellular calcium ions. A calcium ion chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) inhibited the CCh-induced release of calcein. The calcium ionophore, A23187 (2.5 x 10(-6) M), but not 10(-3) M dibutyryl cAMP, evoked the release of calcein. It also increased [Ca2+]i. Removal of extracellular calcium ions suppressed the A23187-induced release of calcein.(ABSTRACT TRUNCATED AT 250 WORDS)