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Electrophysiological effects of acetylcholine in Purkinje fibres surviving infarction
1Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Study Objective:
The aim of the study was to investigate the electrophysiological effects of acetylcholine in Purkinje fibres surviving infarction.
Design:
Infarction in canine hearts was produced by coronary occlusion. Ischaemic tissue was removed and surviving Purkinje fibres were compared for effects of increasing concentrations of acetylcholine (1-100 microM) with control Purkinje fibres from normal hearts and normal Purkinje fibres treated with barium.
Subjects:
Experimental animals were mongrel dogs of either sex, weight 10-15 kg, n = 14 (control), 9 (infarction group), 11 (Ba treated group).
Measurements And Main Results:
Acetylcholine caused concentration dependent shortening of action potential duration in normal Purkinje fibres and in fibres surviving infarction, but had no effect when potassium conductance was decreased with Ba. Acetylcholine induced a small hyperpolarization in normal Purkinje fibres and in fibres surviving infarction perfused with a 4 mM potassium solution without affecting action potential amplitude or dV/dtmax. Reduction in K concentration to 1 and 2 mM caused a greater depolarisation of diastolic potential in normal fibres than in fibres surviving infarction or Ba treated fibres. Acetylcholine produced hyperpolarization under these conditions in normal fibres only. Acetylcholine decreased automaticity in normal fibres only at high concentration (100 microM). A lesser effect was seen in Ba treated fibres and in fibres surviving infarction.
Conclusions:
Since Ba treated Purkinje fibres had similar action potential characteristics to those seen in Purkinje fibres surviving infarction and responded in the same way to the modifications of K concentration, a decrease in K conductance might be the underlying mechanism for some of the electrophysiological changes in fibres surviving infarction. The results also suggest that after 24 h ischaemia, surviving Purkinje fibres have a different sensitivity to acetylcholine from normal fibres.
