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 alpha 1-subunits in hypertrophied myocytes was significantly higher than those in control rats (alpha 1G; 264 +/- 36%, alpha 1H; 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 mu mol/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. (c) 2006 Elsevier Inc. All rights reserved.