Voltage-Dependent Ca²⁺Channels are Involved in Regulation of Steroid Synthesis by Bovine but Not Rat Fasciculata Cells*

Abstract

Bovine but not rat fasciculata cells show a concentration-dependent stimulation of the production of corticosteroids by addition of external Ca2+ to the incubation medium. Both cell types respond to ACTH in a concentration-dependent manner. Increasing concentrations of K+ (0-20 mM) cause increased production of corticosteroids and accelerated influx of Ca2+ in bovine fasciculata cells but no change in either of these two parameters in rat fasciculata cells. Two inhibitors of Ca2+ channels (nifedipine and PY108-068) inhibit both the production of steroids by unstimulated bovine cells and the stimulation produced by three agents (ACTH, (Bu)2 cAMP, and K+). Half-maximal inhibition of these responses was produced in each case by submicromolar or low micromolar concentrations of the inhibitors. These inhibitors are without effect in rat fasciculata cells. One Ca2(+)-channel agonist (BAY K8644) stimulated synthesis of steroids by bovine cells and potentiated the response to ACTH. The agonist acts in the low micromolar range but was without effect on rat cells or on the responses of steroid synthesis by these cells to either ACTH or dibutyryl cAMP. Moreover, bovine fasciculata cells show specific binding sites for [+]PN 200-110, a specific ligand for 1,4-dihydropyridine receptors associated with voltage-dependent Ca2+ channels [dissociation constant (Kd), 14.3 nM; maximum number of binding sites (Bmax), 0.52 pmol/10(6) cells]. Rat cells show no specific binding of PN 200-110. We conclude that bovine fasciculata cells possess voltage-dependent Ca2+ channels which are involved in the regulation of steroid synthesis in these cells and that rat fasciculata cells are without such channels.

Adrenal fasciculata cells express T-type and rapidly and slowly activating L-type Ca2+ channels that regulate cortisol secretion

“…The identity of the voltage-sensitive Ca 2ϩ channels involved in regulating cortisol secretion has also been controversial. Although low voltage-activated T-type Ca 2ϩ channels are the most prominent channels in nearly all bovine, human, and rat AZF cells, L-type Ca 2ϩ channels are also expressed in at least some of these cells (15,42,60). Confusion regarding the role of L-type Ca 2ϩ channels in the regulation of glucocorticoid secretion by ACTH and ANG II arises from several sources.…”

Capacitative calcium entry is involved in steroidogenesis in bovine adrenocortical fasciculata cells

“…6). The tested concentration of nifedipine inhibited high K + -induced steroidogenesis completely in isolated bovine adrenocortical cells (Yanagibashi et al 1990).…”

“…Our results of the inhibitory effects of these cations on [Ca 2+ ] i mobilization are in agreement with those of Hoth & Penner (1993), and suggest a similar mechanism is involved in BAFC. Yanagibashi et al (1990) showed that the steroidogenic effect of ACTH in the presence of extracellular Ca 2+ was completely abolished by dihydropyridines in freshly isolated bovine adrenocortical cells. They proposed the existence of a VOC which was activated by ACTH in BAFC.…”

“…We previously reported that steroidogenesis was facilitated by the entry of Ca 2+ from an extracellular pool as well as by cyclic AMP (Yanagibashi et al 1990). We therefore examined the steroidogenic effect of TG treatment in BAFC.…”

“…However, it was also proposed that Ca 2+ was required for ACTH-induced steroidogenesis (Yanagibashi 1979). We previously showed that bovine adrenocortical fasciculata cells (BAFC) possess a voltage-operated calcium channel (VOC) and that ACTH activates the channel to enhance steroidogenesis (Yanagibashi et al 1990). We also reported that extracellular adenosine 5 -triphosphate (ATP) facilitates steroidogenesis in BAFC via P2Y receptors (Kawamura et al 1991).…”