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Muscarinic Effects on Action Potential Duration and its Rate Dependence in Canine Purkinje Fibers
Author(s) -
MALFATTO GABRIELLA,
ZAZA ANTONIO,
VANOLI EMILIO,
SCHWARTZ PETER J.
Publication year - 1996
Publication title -
pacing and clinical electrophysiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.686
H-Index - 101
eISSN - 1540-8159
pISSN - 0147-8389
DOI - 10.1111/j.1540-8159.1996.tb03274.x
Subject(s) - muscarinic acetylcholine receptor , oxotremorine , purkinje fibers , stimulation , medicine , agonist , endocrinology , biophysics , receptor , electrophysiology , biology
Studies of the autonomic influence on action potential duration (APD) in the ventricles show direct effects of muscarinic stimulation on epicardial, but not endocardial, APD and conflicting results regarding direct vagal effects on the conduction system. In canine Purkinje fibers, we analyzed the action of the M 2 agonist oxotremorine (OXO, 0.1μM) on APD and on its cycle length (CL) dependence. Fibers were impaled with glass microalectrodes and superfused with Tyrode s solution. APD 90 was measured after 3 minutes of drive at CL between 0.3 and 5 seconds. The best fit for the APD/CL relationship at steady state was a hyperbole: APD = APD max *CL/(CL+CL 50 ), where APD max (APD at infinite CL) is a rate independent measure of APD, and CL 50 (CL at which 50% APD max is reached) is an index of the rate dependence of APD. In five fibers, OXO reduced APD at all CL (P < 0.05), APD max was also reduced to 377 ± 41 ms from 447 ± 34 ms (P < 0.05), while CL 50 was unchanged (405 ± 46 ms from 437 ± 28 ms). No effects of OXO on APD and APD max were seen in two fibers obtained from dogs pretreated with pertussis toxin (PTX). In conclusion, stimulation of M 2 receptors in intact, and not PTX treated, Purkinje fibers affects APD but not its CL dependence. This may reflect the activation of a rate independent, background current through a GTP binding protein‐linked pathway, such as, I K .ACH These data differ from those obtained in endocardial and epicardial muscle, stressing the regional differences in vagal modulation of ventricular electrophysiological properties.