GLUCOCORTICOIDS MODULATION OF CALCIUM CURRENTS IN GROWTH HORMONE-3 CELLS

Clonal malignant pituitary growth hormone 3 cells were used for the an alysis of the influence of hydrocortisone and dexamethasone on voltage -gated calcium currents and hormone secretion. The whole-cell patch-cl amp 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 lev el. Some increase in current densities of both components was observed as early as 30 min after treatment with 10(-6) mol/l glucocorticoids. The increase was maximal for both types of currents after 2 h of incu bation; however, the high-threshold component was affected much more s trongly (current density increased by more than four-fold) than the lo w-threshold one (current density increased by about a three-fold). Pot entiation of currents was blocked by actinomycine D (10(-4) M), sugges ting that protein synthesis was required. A substantial increase in gr owth hormone secretion (measured by radioimmunoassay method) was obser ved in the same cells after 2 h of incubation with hydrocortisone, whi le the secretion of prolactin remained even slightly depressed.