Expression of T-type Ca2+Channels in Ventricular Cells from Hypertrophied Rat Hearts

In this study we examined the existence of T-type Ca2+current in ventricular myocytes isolated from rats with pressure-overload hypertrophy. The whole-cell clamp technique was used to record Ca2+currents in enzymatically dissociated ventricular cells. T- and L-type Ca2+currents were separated by applying voltage steps to different test potentials from a holding potential of −80 mV and −50 mV. T-type Ca2+current was defined as the difference between the currents from the two holding potentials. Ventricular myocytes from sham-operated rats showed only L-type Ca2+current (maximal density −13.9±1.3 pA/pFn =17), whereas ventricular myocytes isolated from rats with aortic stenosis showed both L- and T-type Ca2+currents. The average values of T- and L-type Ca2+current density were −4.8±0.4 pA/pF and −12.4±0.9 pA/pF (n=32), respectively. T-type Ca2+current was distinguished from L-type Ca2+current by its voltage dependence, its kinetics and by its strong blockade by nickel 50 μ m. In conclusion, we have demonstrated that hypertrophied ventricular rat cells express T-type Ca2+channels and this finding strongly supports a role for this channel in regulating growth processes in cardiac tissue.