The Effects of Thiocyanate on Mitochondrial Respiration

Abstract

The thiocyanate ion, SCN-, has been extensively employed as a reversible inhibitor of gastric acid secretion. We have reported cytochrome redox changes associated with SCN inhibition in bullfrog gastric mucosa and, since we found no SCN- inhibition of oxygen consumption in tissue mince, concluded that the primary action of SCN- was on the acid secretory mechanism. However, since Forte and Davies have reported SCN- inhibition of oxygen consumption in intact mucosal sheets it seems desirable to determine whether SCN- can inhibit respiration in isolated, functionally intact mitochondria. Materials and Methods. Attempts to prepare mitochondria from bullfrog gastric mucosae and bullfrog liver were unsatisfactory, as judged by the P/O ratio and respiratory control ratio of the particles obtained. Therefore, a standard rat liver mitochondria preparation was employed, in which the mitochondria were reasonably intact by these criteria. The final mitochondrial pellet was suspended in 0.25 M sucrose-0.01 M phosphate buffer, pH 7.1, and all determinations were made in this medium. Oxygen consumption was measured at room temperature with a membrane-covered oxygen electrode fitted to a closed Lucite chamber. The maximum ADP-stimulated respiratory rate (C) was compared to the rate under the same conditions with added SCN- (I) and the result expressed as a ratio (I/C). Results. As an inhibitor of acid secretion in frog gastric mucosa, 2 mM SCN causes an inhibition of 50%, and inhibition is essentially complete at 10 mM. This is in marked contrast to the effect of SCN- on mitochondrial respiration, as shown in Fig. 1. There was no significant respiratory inhibition at concentrations up to 22 mM, which makes it very unlikely that the effect of SCN- on intact mucosal preparations is produced by an inhibition of mitochondrial respiration.