The influence of pH on the use-dependent effects of lidocaine in adult and neonatal canine Purkinje fibers.
We used microelectrode techniques to examine the influence of pH on the effects of lidocaine on neonatal and adult canine Purkinje fiber action potentials. Lidocaine, 5 mg/l and 10 mg/l, significantly decreased overshoot, Vmax, and action potential duration in neonatal and adult fibers (basic cycle length 1300 and 300 ms) at pH 7.3 and 6.8. The effects were similar except for that on action potential duration which was greater in adults. Lidocaine, 5 mg/l, caused a comparable tonic block in adults and neonates at pH 7.3 (12 +/- 2 and 11 +/- 2%, respective decreases of Vmax) and at pH 6.8. Onset of use-dependent block (UDB) (pH 7.3) was faster in adults than neonates, 2 +/- 0.3 vs. 6 +/- 0.8 beats (P < 0.05); and tau off was slower in adults (133 +/- 10 ms) than neonates (81 +/- 8 ms; P < 0.05). At pH 6.8 the 'on' rates were 5 +/- 0.8 and 7 +/- 1 beats for adults and neonates, respectively (P > 0.05), and tau off increased to 210 +/- 15 ms for adults and 193 +/- 10 ms for neonates (P > 0.05). Thus, developmental differences in lidocaine action may be modified by the degree of protonation.
Hamra
M
M
Department of Pharmacology, Columbia University, College of Physicians and Surgeons, New York, NY 10032.
Rosen
M R
MR
D000200:Action Potentials / Q000187:drug effects; D000375:Aging / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D004285:Dogs; D004594:Electrophysiology; D006863:Hydrogen-Ion Concentration; D008012:Lidocaine / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D011690:Purkinje Fibers / Q000187:drug effects* / Q000502:physiology
D008012:Lidocaine