Hemodynamic and electromechanical effects of paraquat in rat heart
Fig 5
Voltage dependence of steady-state Ito activation and inactivation in the absence and presence of 3 μM PQ.
Steady-state inactivation was examined with a double-pulse protocol: A conditioning 400 ms pulse to various potentials ranging from −80 to +10 mV was followed by a test depolarizing pulse to +60 mV (B, inset). The holding potential was −80 mV. The predrug superimposed current traces are shown in A. The inactivation curves for Ito were obtained by normalizing the current amplitudes (I) to the maximal value (Imax) and plotted as a function of the conditioning potentials before and after PQ (n = 5). The activation curves were obtained from the normalized conductance of Ito channels (Gto/Gto, max), which were calculated from the Ito amplitude in Fig 4B and plotted as a function of the depolarizing potentials (n = 5). The solid lines drawn through the data points were best fitted to the Boltzmann equation. (C, D) Effects of PQ on reactivation of Ito. The twin-pulse protocol consisted of two identical 200 ms depolarizing pulses to +60 mV from a holding potential of −80 mV (D, inset), and the prepulse–test pulse interval varied between 10 and 550 ms. An example of the recovery of Ito from inactivation in control conditions is shown in C. The normalized currents (fractional recovery) obtained in the absence and presence of 3 μM PQ were plotted as a function of the recovery time. The solid lines represent a single exponential fit to the data in the absence and presence of 3 μM PQ (n = 5), respectively.