Effect of thymol on kinetic properties of Ca and K currents in rat skeletal muscle

Thymol is widely used as a general antiseptic and antioxidant compound in the medical practice and industry, and also as a stabilizer to several therapeutic agents, including halothane. Thus intoxication with thymol may occur in case of ingestion or improper anesthesia. In the present study, therefore, concentration-dependent effects of thymol (30-600 micro-grams) were studied on calcium and potassium currents in enzymatically isolated rat skeletal muscle fibers using the double vaseline gap voltage clamp technique.

Thymol suppressed both Ca and K currents in a concentration-dependent manner, the EC50 values were 193 +/- 26 and 93 +/- 11 microM, with Hill coefficients of 2.52 +/- 0.29 and 1.51 +/- 0.18, respectively. Thymol had a biphasic effect on Ca current kinetics: time to peak current and the time constant for inactivation increased at lower (100-200 microM) but decreased below their control values at higher (600 microM) concentrations. Inactivation of K current was also significantly accelerated by thymol (200-300 microM). These effects of thymol developed rapidly and were partially reversible. In spite of the marked effects on the time-dependent properties, thymol caused no change in the current-voltage relationship of Ca and K peak currents.

Present results revealed marked suppression of Ca and K currents in skeletal muscle, similar to results obtained previously in cardiac cells. Furthermore, it is possible that part of the suppressive effects of halothane on Ca and K currents, observed experimentally, may be attributed to the concomitant presence of thymol in the superfusate.