Peroxidase secretion from rat lacrimal gland cells in vitro: II. The role of calcium in stimulus-secretion coupling.

The role of calcium in stimulus-secretion coupling in rat lacrimocytes was investigated. Monolayers of lacrimocytes released peroxidase into the incubation medium upon stimulation with calcium ionophore A 23187, L-norepinephrine, L-phenylephrine and tyramine. Our lacrimocyte preparation can be considered free of endogenous catecholamines, because lacrimocytes derived both from normal and from reserpinized rats responded to tyramine with respect to peroxidase secretion. Phenoxybenzamine, cocaine, verapamil and sodiumorthovanadate failed to inhibit the L-phenylephrine-evoked peroxidase secretion. The stimulatory effects of A 23187, L-norepinephrine and L-phenylephrine required extracellular Ca2+ and could be blocked by phentolamine. The action of tyramine was insensitive to all these measures. It is suggested that the stimulus-secretion of peroxidase from lacrimocytes may consist of a Ca2+-dependent phase for stimulants as A 23187, L-norepinephrine and L-phenylephrine and a Ca2+-independent phase for the non-specific tyramine action.