Bis-oxonol experiment on plasma membrane potentials of bovine adrenal chromaffin cells: depolarizing stimuli and their possible interaction.

Changes of plasma membrane potential of isolated bovine adrenal chromaffin cells were monitored by fluorescent probe, bis-[1,3-diethyl-thiobarbiturate]trimethineoxonol (bis-oxonol), which responds to depolarization, resulting in increase of its fluorescence. Excess K+, gramicidin D, veratridine and ouabain all increased bis-oxonol fluorescence. Cells challenged with acetylcholine (ACh) or gamma-aminobutyric acid (GABA) produced a steady-state increase of bis-oxonol fluorescence, reflecting that averaged depolarization occurred continuously. Both effects were dependent on concentration with similar range, and mediated via nicotinic ACh receptor and GABAA receptor, respectively. Application of GABA with ACh or veratridine not only simultaneously but also pretreatedly caused an additive increment of bis-oxonol fluorescence. These results suggest that chromaffin cells in vitro reveal an additively enhanced change of plasma membrane potential in response to the combination of depolarizing stimuli.