PREGNENOLONE SULFATE INCREASES INTRACELLULAR CA2-LINE( LEVELS IN A PITUITARY CELL)

We have investigated the rapid steroid effects on intracellular calciu m ([Ca2+](i) levels in a clonal pituitary cell line (GH3). Among the s teroids tested only pregnenolone sulfate induced a rapid and transient [Ca2+](i) increase within 1 min. The specificity of pregnenolone sulf ate-induced [Ca2+](i) increase with respect to steroid structure was p ronounced. Other steroids (5-40 mu M) including pregnenolone, dehydroe piandrosterone, dehydroepiandrosterone sulfate, progesterone, estradio l-17 beta, testosterone, 5 alpha-dihydrotestosterone, 5 alpha-dihydrop rogesterone, and 3 alpha,5 alpha-tetrahydroprogesterone were found to be ineffective. The [Ca2+](i) increase with pregnenolone sulfate (30 m u M) was completely abolished in a Ca2+-free medium or in the presence of La3+ (0.1 mM) and Co2+ (5 mM). The organic Ca2+ channel blockers m ethoxyverapamil (100 mu M) and nicardipine (5 mu M) both showed simila r inhibitions (> 73%). The interaction between pregnenolone sulfate an d voltage-gated Ca2+ channels (VGCC) was shown by coapplication of pre gnenolone sulfate (10 mu M) With Bay K 8644 (0.1 mM) or KCl (15 mM). C oapplication of pregnenolone sulfate with KCl increased the [Ca2+](i) in an additive manner. However, with the specific agonist Bay K 8644(/-), the pregnenolone sulfate effect was potentiated in a majority of the cells, suggesting cooperative interaction between the two. The res ults demonstrate that pregnenolone sulfate induces a rapid Ca2+ influx in GH3 cells. The marked nicardipine block also suggests that most of the Ca2+ influx is mediated through L-type VGCC.