Mingqi Zheng

17β-Estradiol Modulates Expression of Low-Voltage-Activated CaV3.2 T-Type Calcium Channel via Extracellularly Regulated Kinase Pathway in Cardiomyocytes

T-type Ca(2+) channel current (I(Ca,T)) plays an important role for spontaneous pacemaker activity and is involved in the progression of structural heart diseases. Estrogens are of importance for the regulation of growth and differentiation and function in a wide array of target tissues, including those in the cardiovascular system. The aim of this study was to elucidate the short-term and long-term effects of 17beta-estradiol (E(2)) on I(Ca,T) in cardiomyocytes. We employed in vivo and in vitro techniques to clarify E(2)-mediated modulation of heart rate (HR) in ovariectomized rats and I(Ca,T) in cardiomyocytes. Ovariectomy increased HR and E(2) supplement reduced HR in ovariectomized rats. Slowing of E(2)-induced HR was consistent with the deceleration of automaticity in E(2)-treated neonatal cardiomyocytes. Short-term application of E(2) did not have significant effects on I(Ca,T), whereas in cardiomyocytes treated with 10 nm E(2) for 24 h, estrogen receptor-independent down-regulation of peak I(Ca,T) and declination of Ca(V)3.2 mRNA were observed. Expression of a cardiac-specific transcription factor Csx/Nkx2.5 was also suppressed by E(2) treatment for 24 h. On the other hand, expression of Ca(V)3.1 mRNA was unaltered by E(2) treatment in this study. An ERK-1/2, 5 inhibitor, PD-98059, abolished the effects of E(2) on I(Ca,T) and Ca(V)3.2 mRNA as well as Csx/Nkx2.5 mRNA. These findings indicate that E(2) decreases Ca(V)3.2 I(Ca,T) through activation of ERK-1/2, 5, which is mediated by the suppression of Csx/Nkx2.5-dependent transcription, suggesting a genomic effect of E(2) as a negative chronotropic factor in the heart.

Lysophosphatidylcholine augments Ca(v)3.2 but not Ca(v)3.1 T-type Ca(2+) channel current expressed in HEK-293 cells.

Lysophosphatidylcholine (LPC) has been shown to induce electrophysiological disturbances to arrhythmogenesis. However, the effects of LPC on the low-voltage-activated T-type Ca2+ channels in the heart are not understood yet. We found that LPC increases the T-type Ca2+ channel current (ICa.T) in neonatal rat cardiomyocytes. To further investigate the underlying modulatory mechanism of LPC on T-type Ca2+ channels, we utilized HEK-293 cells stably expressing α1G and α1H subunits (HEK-293/α1G and HEK-293/α1H), by use of patch-clamp techniques. A low concentration of LPC (10 µmol/l) significantly increased Cav3.2 ICa.T (α1H) that were similar to those observed in neonatal rat cardiomyocytes. Activation and steady-state inactivation curves were shifted in the hyperpolarized direction by 5.1 ± 0.2 and 4.6 ± 0.4 mV, respectively, by application of 10 µmol/l LPC. The pretreatment of cells with a protein kinase C inhibitor (chelerythrine) attenuated the effects of LPC on ICa.T (α1H). However, the application of LPC failed to modify Cav3.1 (α1G) ICa.T at concentrations of 10–50 µmol/l. In conclusion, these data demonstrate that extracellularly applied LPC augments Cav3.2 ICa.T (α1H) but not Cav3.1 ICa.T (α1G) in a heterologous expression system, possibly by modulating protein kinase C signaling.