A METHOD FOR ISOLATING RABBIT ATRIOVENTRICULAR NODE MYOCYTES WHICH RETAIN NORMAL MORPHOLOGY AND FUNCTION

This report describes a method for isolating single rabbit atrioventri cular (AV) node myocytes which retain their normal morphology when exp osed to millimolar levels of calcium. Previous attempts to isolate cel ls from the AV node have produced myocytes that ''round up'' (i.e., go into contracture) when exposed to calcium. We show that the cells iso lated with our technique possess properties similar to those described for intact AV nodal tissue. We find that single AV node myocytes are shorter and thinner (mean dimension = 103.5 +/- 2.3 by 7.8 +/- 0.2 mum ; means +/- SE, n = 90) than atrial or ventricular cells. Many of the cells produced by this isolation procedure generate spontaneous action potentials (188 +/- 9 beats/min; n = 6), which resemble action potent ials recorded previously from the intact AV node. Voltage-clamp record ings from spontaneously active cells revealed similar membrane current s to those seen in intact tissue: fast sodium current and a L-type cal cium current, followed by a delayed outward current. However, we found little evidence for the hyperpolarization-activated current (I(f)). B ecause the cells responded normally to concentrations of acetylcholine and isoproterenol within the physiological range, their cholinergic a nd adrenergic receptors appear to be well preserved by the isolation p rocedure. The ability to isolate morphologically and functionally norm al AV myocytes may represent a significant advance for the investigati on of nodal physiology at the cellular level.