Effects of leonurine on L-type calcium channel in rat ventricular myocytes

Leonurine (Leo) is a special alkaloid principle of Herba leonuri that has recently been suggested to improve cardiovascular functions. To date, there is no direct ionic evidence of Leo on regulating calcium channels in the heart. In the present study, we examined the effects of Leo on action potentials and membrane currents recorded from isolated rat ventricular myocytes with the whole-cell patch clamp technique. Leo 100 μM shortened the action potential duration in a dose-dependent manner. Leo up to 200 μM had no significant effect on the Na⁺ current (INa) and K⁺ current (I _K). However, Leo depressed the L-type Ca²⁺ current (I _Ca,L). In the presence of 20 and 100 μM Leo, the current density was decreased and the voltage at half maximal inactivation V_0.5 shift to more negative potential. The recovery time constant was also delayed. In addition, the transcription and protein expression levels of L-type calcium channel (Ca_v1.2) in primary cultured neonatal myocytes from Sprague-Dawley rats were reduced by Leo treatment in a dose-dependent fashion as assessed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assays. We conclude that Leo inhibits L-type calcium channels in cardiomyocytes.