Abstract
Maitotoxin has been reported to activate calcium channels and stimulate calcium-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, we incubated dispersed GH3 pituitary tumor cells in 45Ca2+ with maitotoxin and other agents affecting calcium channels. Within 10 sec of exposure, maitotoxin induced a net calcium influx in cells at isotopic equilibrium. Calcium uptake was concentration dependent between 0.4 and 40 ng/ml maitotoxin and was inhibited by antagonists of voltage-dependent calcium channels but not by inhibitors of sodium channels. PRL and GH release from perifused GH3 cells was stimulated within 1 min by maitotoxin. We conclude that maitotoxin causes a rapid, concentration-dependent influx of calcium through presumed voltage-dependent endogenous calcium channels, culminating in enhanced hormone release. This potent toxin may provide a more precise understanding of the role of calcium in the stimulus-secretion coupling process.
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