Extracellular free calcium and fluid secretion by the rabbit lacrimal gland in vivo

A possible role of extracellular free Ca2+ in methacholine-induced fluid secretion in the in vivo rabbit lacrimal gland has been investigated. Lowering the extracellular Ca2+ concentration by either intra-arterial injection or infusion of EGTA at doses which caused no systemic effects produced a dose related and reversible inhibition of methacholine-induced secretion. The inhibitory effect of EGTA was diminished when EGTA chelated with CaCl2 in varying concentration ratios was administered. On the other hand, intra-arterial injection of CaCl2 potentiated fluid secretion stimulated by submaximal doses of methacholine. These results suggest that fluid secretion from the rabbit lacrimal gland is dependent on the extracellular free Ca2+ concentration.