EFFECTS OF ADRENOCORTICOTROPIN ON ACTION-POTENTIAL AND CALCIUM CURRENTS IN CULTURED RAT AND BOVINE GLOMERULOSA CELLS

Action potentials (APs) and ionic currents were recorded in primary cultured rat and bovine glomerulosa cells by using the whole-cell recording technique. Switching from the current-clamp mode to the voltage-clamp mode allowed recordings of APs and currents in the same cell. APs can be elicited by appropriate stimulation in conditions where the excitability of the cell is increased by blocking a transient outward current. A T-current or a N-current was always present in cells in which APs were recorded; an L-current could also be recorded, but a cell presenting only an L-current was not able to fire an AP. The addition of Bay K 8644 (10(-8) M) induced a dramatic increase in the action potential duration. In the same cells, the analysis of the currents showed that the L-current was increased, whereas the T-current was not significantly affected. The effects of ACTH (10(-8) M) were analysed on APs and currents. On APs, at least two phases could be distinguished, the first corresponded to the reduction of the action potential duration, whereas the second was a huge increase of the plateau duration. The T-current was strongly affected by ACTH as a great inhibition took place in the first seconds after the superfusion with a 10(-8) M ACTH medium. Then a partial recovery of the T-current appeared. The effects of ACTH were reversible on washing. On the contrary, the L-current was increased by ACTH, but this effect was not reversible. The effects of ACTH were mimicked by 8 Bromo cAMP (10(-3) M). Similar results were found in rat and bovine glomerulosa cells. These results suggest that second messengers generated by ACTH would regulate Ca2+ entrance by nondetermined phosphorylation process in the sense of an increase in intracellular Ca2+.