Effect of calcium antagonism or chelation on rabbit lacrimal gland secretion and membrane potentials

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Abstract
ACh[acetylcholine]-induced secretion from the main excretory duct, and ACh-induced hyperpolarizations and resting membrane potentials of superficial, probably acinar, cells were recorded from the rabbit lacrimal gland perfused in vivo with control or test solutions. During perfusion with test solution containing a Ca antagonist, verapamil (10-5 to 10-3 M), or a Ca chelator EGTA [ethylene glycol bis-[.beta.-aminoethyl ether] N,N,N'',N''-tetraacetic acid] (10-4 to 10-3 M), ACh-induced secretion was only 30% of the control value. The magnitude of the ACh-induced hyperpolarization was unchanged. With 10-5 M-verapamil, but not with 10-3 M-verapamil or EGTA-containing solutions, the inhibition of ACh-induced flow was completely reversed by replacing the test with control solution or by increasing the Ca concentration of the test solution 2-fold. EGTA (10-4 M) solution containing the normal extracellular Ca2+ concentration inhibited secretion by 30%. During perfusion with verapamil or EGTA test solutions the mean resting membrane potential of superficial, probably acinar, cells was depolarized by 15%. Although extracellular Ca is required for the major portion of ACh-induced secretion, the magnitude of the ACh-induced hyperpolarization of cells, which are probably acinar, apparently is independent of extracellular Ca.