Publication | Closed Access
Effects of Procaine Amide on Cellular Electrophysiology ofNeonatal and Adult Dog Myocardium
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1980
Year
The electrophysiological effccts of procaine amide wcre studied in normal Purkinje fibers (PF) and ventricular muscle (VM) isolated from 26 newborn puppies ( < 7 days of age) and 6 adult dogs using standard microelectrode techniques. Maximum diastolic potential (MDP), action potential amplitudc (APA), action potential duration at 100% repolarization (APD100) and 50% repolarization (APD50), maximum rate of rise of phase 0 (V max l. membrane responsiveness and effectivc refractory period (ERP) in neonatal PF and VM were unaffected by procaine amide concentrations ranging from 10- 7 to 10^-4 M, (0.03-27 μg/ml). Procaine amide, 5 X 10^-4 M, (136 μg/ml) decreased APA (6%) and Vmax (26%) (p <= 0.05), of neonatal PF while APD100 and ERP incrcased 14 and 23% (p<= 0.05), respectively. Membrane responsiveness of neonatal PF was depressed and shifted downward to the right by 5 X 10- 4 M procaine amide. Exposurc of neonatal VM to 5 X 10^-4 M procaine amide also increased APD100 (14%), and ERP (21%) (p<= 0.05), without affecting othcr measured parameters. In contrast, adult preparations responded to lower procaine amidc levels (<= 30 μg/ml) with an incrcasc in ERP and APD100, 10^-6 -10^-4 M;p<= 0.05) while MDP, APA and Ymax are decreased 10^-4 M; p<= 0.05). Electrophysiological tolerance of newborn cardiac tissue to procaine amide may in part explain the need for increased doses of procaine amide in the human neonate to achieve therapeutic effectiveness.