LIDOCAINE EFFECTS ON ACTION POTENTIALS OF PURKINJE-FIBERS FROM NEONATAL AND ADULT DOGS

Abstract

Effects of lidocaine (L), 2-40 mg/l, on the cellular electrophysiologic properties of Purkinje fibers (PF) from neonatal (0-10 days) and adult dogs. Microelectrode impalements of neonatal and adult PF were selected so that there were no differences between the 2 groups in control maximum diastolic potential, action potential amplitude and maximum upstroke velocity of phase 0 depolarization (.ovrhdot.Vmax). Control action potential duration was significantly shorter in neonates than in adults (P < .05). At a superfusate K+ concentration of 4 mmol/l, the threshold concentration for L effects on action potential amplitude in neonates was 40 mg/l and in adults, 20 mg/l; on .ovrhdot.Vmax in neonates threshold was 5 mg/l and in adults was 2 mg/l; on action potential duration in neonates and adults threshold was 2 mg/l. The effect of L on adult PF action potentials was greater than on neonatal PF. The effects of L on action potential duration also suggest that K conductance may be greater in neonatal fibers. When superfusate K+ concentration was increased to 6 mM the effects of L on adult PF were potentiated more than on neonates. Experimental evidence of the age-related changes in sensitivity of the specialized conducting system to cardioactive drugs is provided.