Effect of sodium pentobarbital on the transmembrane action potential and the slow inward current of guinea pig ventricular myocytes.

Barbiturates, which are widely used in clinical anesthesia, exert a negative inotropic effect on the myocardium. To investigate the mechanism for the negative inotropism, we studied the effect of sodium pentobarbital (SP) on the action potential and the slow inward current recorded from guinea pig ventricular myocytes. We found that SP at 0.6, 1.0, and 1.6 microM decreased action potential duration at 50% repolarization by 17 +/- 6, 25 +/- 11, and 29 +/- 8%, respectively (p less than 0.05, n = 4). At the concentration range of 0.6-1.6 microM, resting potential and action potential amplitude were unaffected. Voltage-clamp studies in ventricular myocytes demonstrated that SP at 0.6, 1.0, and 1.6 microM reduced the peak slow inward current by 30 +/- 4, 36 +/- 14, and 67 +/- 5%, respectively (p less than 0.005, n = 4). In conclusion, SP, a frequently used anesthetic, decreases the slow inward current in guinea pig ventricular myocytes at clinically relevant concentrations.