Abstract
Thyrotropin-releasing hormone (TRH) or 50 mM K + stimulated the acute release of prolactin from the GH 4C 1 strain of rat pituitary cells in culture. The enhanced release of prolactin was inhibited in a dose-related manner by the Ca +2 antagonist Co +2 (2.0 to 0.5 mM) as well as by the Ca +2 chelator EGTA (1.0 mM). Co +2 also reduced spontaneous basal prolactin release. There was partial reversal of the inhibitory effect of Co +2 (2.0 mM) by Ca +2 (2.0 mM) and complete reversal of the inhibitory effect of EGTA (1.0 mM) by Ca +2 (2.0 mM). The enhanced release of prolactin stimulated by 50 mM K + was maximal by 10–20 minutes in medium containing 0.67 to 0.74 mM Ca +2. Na + (50 mM) did not mimic the effect of high K +. We conclude that Ca +2 is an essential cation in mediating the actions of high external K + and TRH on the release of prolactin by GH 4C 1 cells.
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