Effects of tocainide and lidocaine on the transmembrane action potentials as related to external potassium and calcium concentrations in guinea-pig papillary muscles.

摘要: Effects of lidocaine and tocainide on transmembrane potentials were studied in isolated guineapig papillary muscles, superfused with modified Tyrode's solution containing either 5.4, 2.7, 10.0 or 8.1 mmol/l potassium concentration, [K]0. The last applied contained 1.8 (normal [Ca]0) 7.2 (high [Ca]0). concentrations used 18.5, 36.9 73.9 μmol/l 43.7, 87.5 174.9 5.4 [K]0 the other solutions, respectively. At driving rate 1 Hz solution, both drugs produced dosedependently a reduction maximum rise action potential ( $$\dot V_{\max } $$ ), together prolongation relative refractory period. decreased progressively as was increased from (for lidocaine) 0.25 tocainide) to 5 Hz. This accentuated dose-depently. A slow component (time constant τ=195–232 ms for lidocaine, 281–303 slower (τ=2.1–3.8 s recovery (reactivation) observed premature responses at first response after interruption basic All these effects rising attenuated high [Ca]0 solution. Both abbreviated duration 50% (APD50) 90% (APD90) levels but not 2.7 nor These [K]0-dependent successfully simulated by model proposed Hondeghem Katzung (1977), slight change parameter values. mode interaction sodium channels open, closed rested states deduced results.