ABSTRACT
Objective To evaluate the effects of propofol and thiopontal on calcium and potassium channels in rat ventricular myocytes and to elucidate the underlying mechanisms of their inhibitory effect on myocardium. Methods Freshly isolated ventricular myocytes were prepared from hearts of rats by trypsin. The effects of propofol and thiopental on L-type calcium current(Ica) and delayed rectifier potassium current(IK)were compared using whole-cell patch clump technique. Results Propofol and thiopontal produced a concentration-dependent inhibition of Ica. Peak concentration of propofol(50 ?mol?L~(-1)) and thiopental(100 ?mol?L~(-1)) during induction of anesthesia decreased Ica by 28% and 46% and shifted the steady-state inactivation curve to more negative voltage, but had no effect on the steady-state activation curve. Propofol and thiopental also decreased IK in a concentration-dependent manner, but the effects of both anesthetics on IK were smaller compared with their effects on Ica. Conclusion The findings of this study suggest that the negative inotropic of propofol and thiopental are, at least in part, related to decrease in Ca~(2+) trans-sarcolemmal current by accelerating L-type calcium channel inactivation. Both anesthetics decrease delayed rectifier potassium current, thus partially antagonizing the effect of decreased calcium current.
ABSTRACT
To study the dynamic process of myocardial uptake of thiopentai in the isolated rabbit hearts. Method: Thiopental at doses of 500?mol, 1500?mol and 500?mol was given sequentially to the perfused rabbit heart in a total time of 15 min. The outflow concentration of thiopental was measured with high performance liquid chromatography and the left ventricular +dp/dtmax served as a effective parameter. Resuh: The disposition and elimination of thiopental can be best described hy a two-compartment open model. It can disposed into myocardium rapidly (T_(1/2)?=0.5?0.1 min), but elimination was relatively slow (T_(1/2)?=25.3?10.1 min). The transfer rate was slower from peripheral to central compartment than from central to peripheral compartment. The tbeoritical maximum depressant effect of thiopental on + dp/dt (Emax) was 19.0 4-11.2 kPa.s~(-1) corresponding to 1/10 E_0. Conclusion: The myocardial uptake of thiopental can be fitted to a two-compartment open model with rapid disposition and relative slow elimination process.
