The Effect of Levobunolol Hydrochloride on the Calcium andPotassium Channels in Isolated Ventricular Myocytes of Guinea Pig

The effect of levobunolol hydrochloride on the calcium and potassium channels in isolated ventricular myocytes of guinea pig

Summary The effects of levobunolol hydrochlorid (Bun) on the type L calcium channel currents (I_ca and delayed rectifier potassium channel currents (I_k) in isolated ventricular myocytes of guinea pig were studied by using patch clamp whole cell recording techniques. The results were showed that: 1) Bun caused a dosedependent decrease in I_ca and a dose-dependent increase in I_k of the ventricular myocytes. The threshold concentrations of Bun for I_ca and I_k were 10⁻⁸ mol/L and 10⁻⁷ mol/L respectively. The maximum effective concentration of Bun for both I_ca and I_k was 3 × 10⁻⁵ mol/L, and half-maximal concentration Was 3 × 10⁻⁶ mol/L; 2) I_k was blocked by 2 × 10⁻⁶mol/L tetraethylammonium (TEA). A concentration of 3 × 10⁻⁶ mol/L Bun showed a decreasing effect on the Ic as revealed by the current-voltage relationship curve, i.e., Bun caused an elevation of the curve; 3) When I_ca was blocked by 2X10⁻⁶ mol/L Isoptin (Verapamil), at a concentration of 3 × 10⁻⁶ mol/L Bun showed an increasing effect on Ik and the effect could be blocked by TEA- The above-mentioned results indicated that Bun had an inhibitory effect on I_ca and a fascilitatory effect on I_k. The results suggested that the molecular mechanisms of antihypertensive, heart rate slowing and β-receptor blocking effects of Bun might be due to decrease of I_ca and increase of I_k. This project was supported by Science Committee of Hubei Province (No. 95 JJ9-29).