THE EFFECT OF TETRODOTOXIN ON CALCIUM-DEPENDENT LINK IN STIMULUS-SECRETION COUPLING IN NEUROHYPOPHYSIS

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Abstract
Studies have been made on the effect of tetrodotoxin for vasopressin release from the isolated pituitary gland of the rat and Ca movement in relation to the secretion. The presence of tetrodotoxin in incubation media suppressed markedly (80%) the vasopressin release caused by the exposure of the gland to excess K solution. Such a suppression can also persist in Na-deficient media. 45Ca movements of both efflux and influx under the exposing excess K are also suppressed by about 35%. However, apparent suppression by tetrodoxtoxin on vasopressin release and Ca movement were not seen at the resting state. The potentiation of secretion caused by low temperature or the presence of SH reagent was not suppressed by tetrodotoxin. The primary effect of tetrodotoxin is a suppression of the Ca movement in stimulus-secretion coupling, then secondarily the vasopressin output is suppressed. Electron microscopic observations are consistent with the experiment of vasopressin release.