Cyclic AMP-induced depolarization measured by bis-oxonol fluorescence in bovine adrenal medullary chromaffin cells.

Effects of cyclic AMP on membrane potentials were examined by measuring the changes of bis-oxonol fluorescence in bovine adrenal medullary chromaffin cells. 8-Bromo cyclic AMP (8Br-cAMP) or forskolin caused a gradual and long lasting increase of the fluorescence intensity. The effects of 8br-cAMP was blocked by cyclic AMP-dependent protein kinase inhibitor, adenosine-3', 5'-cyclic monophosphothioate, Rp-diastereomer (Rp-cAMPS) and there was no further increase in the fluorescence by 8br-cAMP in the cells depolarized with 56 mM KC1 or gramicidin D. Ouabain or the removal of extracellular K+ ([K+]0 free) which block Na+, K+-ATPase also increased the fluorescence. The effect of 8br-cAMP on the fluorescence was counteracted by ouabain or [K+]0 free and was blocked in the absence of extracellular Na+ but not by tetrodotoxin or the removal of Ca2+ from the medium. These results may suggest that cyclic AMP causes the membrane depolarization by accumulating Na+ through the inhibition of Na+, K+-ATPase in adrenal chromaffin cells.