Electrophysiology and ultrastructure of canine subendocardial Purkinje cells isolated from control and 24-hour infarcted hearts.

Abstract

Ventricular arrhythmias that accompany myocardial infarction in dogs may be secondary to the altered electrophysiological properties of the subendocardial Purkinje fibers that survive 24 hours after the coronary occlusion. To better understand the ionic mechanisms that underlie the altered electrical activity of these fibers, we have dispersed, using an enzymatic technique, Purkinje cells from the subendocardium of the infarcted ventricle (IZPCs) and compared their electrical and structural properties to Purkinje cells dispersed from fiber strands ( S erious ventricular arrhythmias often occur in humans immediately after coronary artery occlusion and during the "in hospital" phase of patient therapy, as well as for weeks to years after the infarction. 1 -2 Several hypotheses maintain that the mechanisms of these cardiac arrhythmias can be understood in terms of specific alterations in cellular electrical activity that result from the myocardial infarction. 34Much of what is known about the cellular electrophysiological changes that occur during these phases of arrhythmias has been derived from experiments on isolated tissues, either excised at difFrom the Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, New York.Supported by Grant HL-34477 from the National Institutes of Health, Bethesda, Maryland.Address for correspondence: Dr. Penelope Boyden, Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032.Received June 13, 1988; accepted April 17, 1989. ferent times after the coronary artery occlusion or taken from normal hearts and superfused with solutions altered in such a way as to mimic conditions in ischemic hearts. Microelectrode studies on the isolated canine myocardium have shown 1) that Purkinje fibers survive on the endocardial surface of infarcts after the muscle has died; 2) that marked changes in the transmembrane action potentials of these surviving subendocardial Purkinje fibers occur at the time when the delayed phase of ventricular arrhythmias occurs; and 3) that the changes in the membrane potentials of these Purkinje fibers could cause arrhythmias. 5 " 7 Specifically, the maximum diastolic potential, action potential amplitude, and maximum rate of depolarization are reduced in Purkinje fibers in the subendocardium of the ventricles 24 hours after the coronary artery occlusion when compared with control subendocardial fibers.

Wide long lasting perinuclear Ca2+ release events generated by an interaction between ryanodine and IP3 receptors in canine Purkinje cells

“…Purkinje cells were enzymatically dispersed from the Purkinje fibers of the canine heart (preparations=N=15) as previously described [11,12] and placed in a glass-bottomed perfused chamber on the stage of an inverted microscope and then loaded with 5µM Fluo-4 AM [9]. Fluorescence was measured only in rod-shaped Purkinje cells with typical junctional ends, clear striations and membranes free of blebs.…”

2APB- and JTV519(K201)-sensitive micro Ca2+ waves in arrhythmogenic Purkinje cells that survive in infarcted canine heart

“…7 Briefly, small strips (4 × 2 × 2 mm) of left ventricular endocardium containing longitudinally oriented Purkinje fiber bundles were carefully dissected from larger preparations removed from specific regions in the control and infarcted hearts. Strips prepared from infarcted hearts were taken from subendocardium directly overlying the infarcted portion of the left ventricle.…”

“…Strips prepared from infarcted hearts were taken from subendocardium directly overlying the infarcted portion of the left ventricle. 7 Cell aggregates were studied in a chamber on the stage of an epifluorescence microscope and superfused with normal Tyrode's solution containing the following (in mM): NaCl 137, NaHCO 3 24, NaH 2 PO 4 1.8, MgCl 2 0.5, CaCl 2 2.0, KCl 4.0, and dextrose 5.5 (pH 7.4; 24°-25°C). We previously established that this model is suitable for fluorescence studies of intracellular [Ca 2+ ].…”

“…We previously established that this model is suitable for fluorescence studies of intracellular [Ca 2+ ]. 4 , 8 Aggregate/cell selection for fluorescence measurements Cell aggregates were selected for study based on previously determined criteria, 4 , 7 , 8 that is, only Purkinje cell aggregates that were rod shaped with typical junctional ends (fingerlike projections), 7 clear striations, and surface membrane free of blebs were used. For some experiments, we selected aggregates of Fluo-3/AM loaded Purkinje cells that exhibited nondriven rhythmic activity.…”

Small‐Conductance Calcium‐Activated Potassium Current in Normal Rabbit Cardiac Purkinje Cells

“…The cell isolation protocol was modified from published methods 17. The rabbits underwent isoflurane inhalation general anesthesia.…”