Pharmacological effects of carvedilol on T-type calcium current in murine HL-1 cells

Carvedilol is widely used in the treatment of cardiovascular diseases including atrial fibrillation. T-type Ca2+ channels have been recognized recently in the mechanisms underlying atrial arrhythmias. However, it is unclear whether carvedilol may affect the T-type Ca2+ channel. The present study evaluated the pharmacological effects of carvedilol on T-type calcium current (I-Ca,I-T) in the murine HL-1 cell line. I-Ca,I-T was recorded by the whole-cell patch-clamp technique. Calcium transient was monitored by the fluorescent dye Fluo-4/AM and confocal laser scanning microscopy. Carvedilol reversibly inhibited I-Ca,I-T in a concentration-dependent manner, with an IC50 of 2.1 mu M. 3 mu M carvedilol was found to decrease the peak I-Ca,I-T amplitude at -20 mV from 20.1 +/- 1.8 pA/pF to 10.9 +/- 2.1 pA/pF. Carvedilol significantly shifted the steady-state inactivation curve of I-Ca,I-T towards more negative potential by 12.8 mV, while the activation curve was not significantly altered. Carvedilol delayed recovery from inactivation of I-Ca,I-T, time constant (tau) Was 112.4 +/- 3.5 ms in control and 270.1 +/- 4.7 ms in carvedilol. Carvedilol-induced inhibition rate in I-Ca,I-T Was enhanced with the increase in stimuli frequency, the inhibitory rate was 23.2 +/- 4.1% at 0.2 Hz and 47.2 +/- 0.6% at 2 Hz. Carvedilol still produced the significant decrease in the amplitude of I-Ca,I-T in the presence of H-89, PKA inhibitor. Carvedilol significantly inhibited the amplitude of the calcium transient in a concentration-dependent manner. These findings indicate that carvedilol inhibits I-Ca,I-T in atrial cells by mechanisms involving preferential interaction with the inactivated state of T-type Ca2+ channel. (C) 2009 Elsevier B.V. All rights reserved.