Electrophysiological interactions between carbachol and class I antiarrhythmic drugs (lidocaine, quinidine)—experimental studies in rabbit atrial myocardium

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Abstract
Cholinergic agents exert no direct effect on the fast Na+ inward current but may influence the binding characteristic of class I antiarrhythmic drugs in atrial myocardium by shortening the action potential (AP) duration or by increasing the resting potential (RP). In order to examine such possible interactions we performed experiments using conventional intracellular microelectrodes on isolated preparations of rabbit atrial myocardium (Ke 2.7 mM, temperature 32°C). At first the influence of the cholinergic agent carbachol (1 mg/l=6.7×10−6 M) on the RP and AP was examined at different stimulation rates (1.0, 2.5, and 3.3 Hz). Thereafter measurements were repeated under the influence of lidocaine (10 mg/l=2.2×10−5 M) or quinidine (5 mg/l=2.2×10−5M) alone and in combination with carbachol (1 mg/l).