Stimulus-secretion coupling in the rat lacrimal gland

The role of calcium in stimulus-secretion coupling in the lacrimal gland was investigated. Rat exorbital lacrimal gland slices released peroxidase into the incubation medium after muscarinic or alpha-adrenergic receptor stimulation. In both cases, secretion appeared to involve exocytosis as revealed by electron microscopy. Secretion due to the muscarinic agonist carbachol was inhibited by Ca omission and by lanthanum. Secretion due to the alpha-adrenergic agonist phenylephrine was inhibited by Ca omission at 10(-5) M concentration but not at 10(-4) M concentration. The effects of 10(-4) M phenylephrine could be blocked by lanthanum or by reduction of extracellular Na. Both agonists stimulated 45Ca efflux, but phenylephrine was less efficacious. These results suggest that the agonists may cause exocytosis by stimulating influx of Ca or release of cellular Ca. Sodium may play a role in the Ca-release mechanism.