A calcium ionophore-induced secretion in rabbit lacrimal gland in vivo

Local administration of the calcium ionophore, A-23187 increased basal fluid secretion (non-stimulated) from the cannulated main excretory duct of rabbit lacrimal gland in vivo. A-23187 also facilitated fluid secretion induced by submaximal dose of methacholine (0.1 μg/kg, intraarterially). The stimulatory effect of A-23187 was dependent on the extracellular calcium concentration. Lowering the extracellular calcium by addition of EGTA markedly depressed or abolished the responses to the ionophore while increasing the extracellular calcium with CaCl₂ enhanced it. The results suggest that A-23187 causes increase in cell membrane permeability to extracellular calcium and the rise in intracellular calcium activates the secretory process(es) by an unknown mechanism to produce fluid secretion in the rabbit lacrimal gland.