Clonal malignant pituitary growth hormone 3 cells were used for the analysis of the influence of hydrocortisone and dexamethasone on voltage-gated calcium currents and hormone secretion. The whole-cell patch-clamp technique was used. The presence of low-threshold inactivating and high-threshold persisting components in the total calcium current was shown; they could be separated at less negative holding potential level. Some increase in current densities of both components was observed as early as 30 min after treatment with 10-6mol/1 glucocorticoids. The increase was maximal for both types of currents after 2 h of incubation; however, the high-threshold component was affected much more strongly (current density increased by more than four-fold) than the low-threshold one (current density increased by about a three-fold). Potentiation of currents was blocked by actinomycine D (10 -4 M), suggesting that protein synthesis was required. A substantial increase in growth hormone secretion (measured by radioimmunoassay method) was observed in the same cells after 2 h of incubation with hydrocortisone, while the secretion of prolactin remained even slightly depressed.
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