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 mu m shortened the action potential duration in a dose-dependent manner. Leo up to 200 mu m had no significant effect on the Na+ current (I-Na) and K+ current (I-K). However, Leo depressed the L-type Ca2+ current In the presence of 20 and 100 mu m 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-Hawley 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.
[1]Fudan Univ, Dept Pharmacol, Sch Pharm, Shanghai 201203, Peoples R China.
[2]Fudan Univ, Dept Physiol & Pathophysiol, Shanghai Med Coll, Shanghai 200032, Peoples R China.
[3]Emory Univ, Sch Med, Div Renal, Dept Med, Atlanta, GA 30322 USA.
[4]Atlanta Vet Adm Med Ctr, Renal Sect, Decatur, GA 30033 USA.
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