Gramicidin toxicity in NG108-15 cells: protective effects of acetamidine and guanidine

Studies were conducted using a novel in vitro approach to investigate the efficacy of acetamidine hydrochloride (ACE) and guanidine hydrochloride (GUAN), previously shown to block gramicidin D (GRAM) channels in artificial membranes, in preventing the toxic effects of GRAM in NG108-15 (neuroblastoma×glioma hybrid) cells. Specifically, intracellular microelectrode techniques were employed to examine changes in membrane resting potential (V_m) and input resistance (R_in). At 1 mol/L, ACE significantly reduced loss of V_m induced by 1 or 10 g/ml GRAM, although higher concentrations of ACE did not afford enhanced antagonism. GUAN, in contrast, produced a concentration-dependent antagonism of GRAM-induced V_m and R_in loss, with high concentrations (10 or 100 mol/L) completely preventing diminutions in both V_m and R_in. In control cells superfused without GRAM, ACE produced a direct, concentration-dependent reduction in V_m and R_in, whereas GUAN hyperpolarized NG108-15 cells but did not alter R_in. These data represent the initial demonstration of the reversal of GRAM toxicity in an intact cell system.