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.

Voltage-dependent L-type calcium channels (VDCC) play important roles in many cellular processes. The interaction of the actin cytoskeleton with the channel in nonexcitable cells is less well understood. We performed whole-cell patch-clamp surface biotinylation and calcium imaging on different osteoblast cells to determine channel kinetics, amplitude, surface abundance, and intracellular calcium, respectively. Patch-clamp studies showed that actin polymerization by phalloidin increased the peak current density of I Ca , whereas actin depolymerization by cytochalasin D (CD) significantly decreased the current amplitude. This result is consistent with calcium imaging, which showed that CD significantly decreased Bay K8644-induced intracellular calcium increase. Surface biotinylation studies showed that CD is not able to affect the surface expression of the pore-forming subunit α 1C . Interestingly, application of CD caused a significantly negative shift in the steady-state inactivation kinetics of I Ca . There were decreases in the voltage at half-maximal inactivation that changed in a dose-dependent manner. CD also reduced the effect of activated vitamin D 3 (1α,25-D3) on VDCC and intracellular calcium. We conclude that in osteoblasts the actin cytoskeleton affects α 1C by altering the channel kinetic properties, instead of changing the surface expression, and it is able to regulate 1α,25-D3 signaling through VDCC. Our study provides a new insight into calcium regulation in osteoblasts, which are essential in many physiological functions of this cell.

Transient receptor potential channel (TRPC) family,which functions as a non-selective cation channel, allows the entry of Na+ and Ca2+ ions into the cells.Different homomeric or heteromeric TRPC channels regulate various physiological functions in smooth muscle and endothelial cells of blood vessel.Abnormal TRPC expressions,which is the important underlying molecular mechanism of vascular remodeling,may be responsible for pathophysiological processes of hypertension as well as increased endothelial permeability.Thus,investigating the roles of TRPC ion channels in the pathogenesis of vascular remodeling provides new therapeutic approach to the related disease.