Membrane potential changes induced by the ouabain-like compound extracted from mammalian brain.

Abstract

The electrical membrane potential (.DELTA. .PSI.) of chicken embryo fibroblasts in tissue culture was determined to be -30.5 .+-. 2.9 mV as measured by distribution of the lipophilic [3H]tetraphenylphosphonium cation (Ph4P+). Stimulation of the electrogenic activity of the Na+, K+-ATPase by the ionophore monensin induces a hyperpolarization of .apprxeq. 47 mV and a new .DELTA. .PSI. of -77.3 .+-. 5.7 mV. The effects of the cardiac glycoside ouabain and an ouabain-like compound (OLC), which was extracted and partially purified from sheep brain, were contrasted using both the resting and hyperpolarized fibroblasts. Addition of OLC or ouabain to the incubation medium for short periods of time does not alter the cells'' resting .DELTA. .PSI.. OLC and ouabain block monensin-induced hyperpolarization. The inhibitory effects of OLC, like ouabain, are dose dependent, with half-maximal inhibition occurring at an amount of OLC equivalent to that found in 1.6 g of brain (wet weight) per ml and at 0.85 .mu.M ouabain. The maximal actions of ouabain and OLC are not additive. These results show that the endogenous OLC specifically affects the .DELTA. .PSI. of intact cells by a mechanism analogous to that of ouabain, i.e., inhibition of the Na+, K+-ATPase.