Calcium Ion as a Second Messenger for o-Nitrophenylsulfenyl-Adrenocorticotropin (NPS-ACTH) and ACTH in Bovine Adrenal Steroidogenesis

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This work was supported, in part, by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan (09680623, Priority Area 09235223).

Abstract

o-Nitrophenyl sulfenyl-modified ACTH (NPS-ACTH) stimulated steroidogenesis acutely in bovine fasciculata-reticularis cells without increase in cellular cAMP synthesis. Application of NPS-ACTH to the cultured cells induced Ca²⁺ signals in individual cells as detected by video-enhanced microscopic fluorescence measurements. The percentage of Ca²⁺ signaling cells corresponded well with the increase of steroidogenesis induced by NPS-ACTH below 1 nm. Treatment of the cells with nicardipine, a Ca²⁺ channel blocker, suppressed the Ca²⁺ signals except for the transient increase just after the addition of NPS-ACTH and also blocked completely the stimulative effect on the steroidogenesis of NPS-ACTH below 1 nm. At a dosage of NPS-ACTH higher than 10 nm, the stimulative effect of steroidogenesis was partly suppressed by nicardipine and also by AA-861, a lipoxygenase inhibitor. The action of NPS-ACTH might be mediated by both Ca²⁺ and lipoxygenase metabolite(s) of arachidonic acid as dual second messengers. The effect of ACTH in pm range on the steroidogenesis was suppressed completely by the treatment with nicardipine and AA-861 at the same time, indicating that the action was mediated by both Ca²⁺ and the lipoxygenase metabolite(s) but not by cAMP. cAMP plays a significant role as a second messenger for ACTH action only at ACTH concentrations greater than 10 pm.