The Effects of Maitotoxin on45Ca2+Flux and Hormone Release in GH3 Rat Pituitary Cells*

Abstract

Maitotoxin was reported to activate Ca channels and stimulate Ca-dependent functions in several tissues, but a thorough investigation of 45Ca2+ fluxes is lacking. To characterize the influence of maitotoxin on 45Ca2+ flux in greater detail, dispersed GH3 pituitary timor cells were incubated in 45Ca2+ with maitotoxin and other agents affecting Ca channels. Within 10 sec of exposure, maitotoxin induced a net Ca influx in cells at isotopic equilibrium. Ca uptake was concentration dependent between 0.4 and 40 ng/ml maitotoxin and was inhbiited by antagonists of voltage-dependent Ca channels but not by inhibitors of Na channels. PRL [prolactin] and GH [growth hormone] release from perfused GH3 cells was stimulated within 1 min by maitotoxin. Maitotoxin causes a rapid, concentration-dependent influx of Ca through presumed voltage-dependent endogenous Ca channels, culminating in enhanced hormone release. This potent toxin may provide a more precise understanding of the role of Ca in the stimulus-secretion coupling process.