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CARDIOVASCULAR

Inhibition of Na⁺-K⁺ Pump and L-Type Ca²⁺ Channel by Glibenclamide in Guinea Pig Ventricular Myocytes

Department of Life Science, Pohang University of Science and Technology, Pohang, Kyung-buk, Republic of Korea

Glibenclamide, a potent cystic fibrosis transmembrane conductance regulator (CFTR) Cl^– channel blocker, is frequently used to study function and regulation of CFTR Cl^– channels. In this study, the effects of glibenclamide on intracellular Na⁺ concentration ([Na⁺]_i), contraction, Ca²⁺ transient, and membrane potential were investigated in isolated guinea pig ventricular myocytes. Glibenclamide increased [Na⁺]_i and decreased contraction and Ca²⁺ transient. However, glibenclamide did not change membrane potential. To determine whether inhibition of Na⁺-K⁺ pumps and L-type Ca²⁺ channels is responsible for the increase of [Na⁺]_i and the decrease of contraction, we tested the effects of glibenclamide on Na⁺-K⁺ pump current and L-type Ca²⁺ current (I_Ca,L). Glibenclamide decreased Na⁺-K⁺ pump current and I_Ca,L in a concentration-dependent manner. In the presence of Cl^– channel inhibitors, glibenclamide depolarized diastolic membrane potential and reduced action potential duration. This result suggests that the reason for lack of effect of glibenclamide on membrane potential might be due to its combined inhibitory effects on the Na⁺-K⁺ pump, the L-type Ca²⁺ channel, and Cl^– channels, which may have opposing effects on membrane potential. These results indicate that glibenclamide increases [Na⁺_i] by inhibiting the Na⁺-K⁺ pump and decreases contraction and Ca²⁺ transient, in addition, by blocking the L-type Ca²⁺ channel.

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