Pregnenolone sulfate increases intracellular Ca2+ levels in a pituitary cell line.

Abstract We have investigated the rapid steroid effects on intracellular calcium ([Ca 2+ ] i levels in a clonal pituitary cell line (GH3). Among the steroids tested only pregnenolone sulfate induced a rapid and transient [Ca 2+ ] i increase within 1 min. The specificity of pregnenolone sulfate-induced [Ca 2+ ] i increase with respect to steroid structure was pronounced. Other steroids (5–40 μM) including pregnenolone, dehydroepiandrosterone, dehydroepiandrosterone sulfate, progesterone, estradiol-17β, testosterone, 5α-dihydrotestosterone, 5α-dihydroprogesterone, and 3α,5α-tetrahydroprogesterone were found to be ineffective. The [Ca 2+ ] i increase with pregnenolone sulfate (30 μM) was completely abolished in a Ca 2+ -free medium or in the presence of La 3+ (0.1 mM) and Co 2+ (5 mM). The organic Ca 2+ channel blockers methoxyverapamil (100 μM) and nicardipine (5 μM) both showed similar inhibitions (> 73%). The interaction between pregnenolone sulfate and voltage-gated Ca 2+ channels (VGCC) was shown by coapplication of pregnenolone sulfate (10 μM) with Bay K 8644 (0.1 mM) or KCl (15 mM). Coapplication of pregnenolone sulfate with KCl increased the [Ca 2+ ] 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 results demonstrate that pregnenolone sulfate induces a rapid Ca 2+ influx in GH3 cells. The marked nicardipine block also suggests that most of the Ca 2+ influx is mediated through L-type VGCC.