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/pF: n = 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 mu M. In conclusion. we have demonstrated that hypertrophied ventricular rat cells express T-type Ca2+ channels and this finding strongly supports a rule fur this channel in regulating growth processes in cardiac tissue. (C) 1999 Academic Press.