Remodeling excitation-contraction coupling of hypertrophied ventricular myocytes is dependent on T-type calcium channels expression

We utilized Wistar rats with monocrotaline (MCT)-induced right ventricular hypertrophy (RVH) in order to evaluate the T-type Ca²⁺ channel current (I_CaT) for myocardial contraction. RT-PCR provides that mRNA for T-type Ca²⁺ channel α1-subunits in hypertrophied myocytes was significantly higher than those in control rats (α1G; 264 ± 36%, α1H; 191 ± 34%; P < 0.05). By whole-cell patch-clamp study, I_CaT was recorded only in hypertrophied myocytes but not in control myocytes. The application of 50 nmol/L nifedipine reduced the twitch tension of the right ventricles equally in the control and RVH rats. On the other hand, 0.5 μmol/L mibefradil, a T-type Ca²⁺ channel blocker, strongly inhibited the twitch tension of the RVH muscle (control 6.4 ± 0.8% vs. RVH 20.0 ± 2.3% at 5 Hz; P < 0.01). In conclusion, our results indicate the functional expression of T-type Ca²⁺ channels in the hypertrophied heart and their contribution to the remodeling of excitation-contraction coupling in the cardiac myocyte.