Nature of the Schwann cell electrical potential. Effects of the external ionic concentrations and a cardiac glycoside

Abstract

The effects on the Schwann cell electrical potential of external ionic concentrations and of K-strophanthoside were investigated. Increasing (K)(o) depolarized the cell. The potential is related to the logarithm of (K)(o) in a quasi-linear fashion. The linear portion of the curve has a slope of 45 mv/ten-fold change in (K)(o). Diminutions of (Na)(o) and (Cl)(o) produced only small variations in the potential. Calcium and magnesium can be replaced by 44 mM calcium without altering the potential. Increase of (Ca)(o) to 88 mM produced about 10 mv hyperpolarization. The cell was hyperpolarized by 11 mv and 4 mv within 1 min after applying K-strophanthoside at concentrations of 10(-3) and 10(-5)M, respectively. No variations of cellular potassium, sodium, or chloride were observed 3 min after applying the glycoside. The hyperpolarization caused by 10(-3)M K-strophanthoside was not observed when (K)(o) was diminished to 1 or 0.1 mM or was increased to 30 mM. At a (K)(o) of 30 mM, 10(-2)M strophanthoside was required to produce the hyperpolarizing effect. In high calcium, the cell was further hyperpolarized by the glycoside. The initial hyperpolarization caused by the glycoside was followed by a gradual depolarization and a decrease of the cellular potassium concentration. The results indicate that the Schwann cell potential of about -40 mv is due to ionic diffusion, mainly of potassium, and to a cardiac glycoside-sensitive ion transport process.