Membrane properties of aggregate of collagenase-dissociated rat heart cells

Aggregates of collagenase-dissociated neonatal rat heart cells have been tested for several membrane properties and shown to be comparable with cells from the intact heart. Action potentials, recorded from driven aggregates, are fully suppressed by tetrodotoxin (TTX). Under Mn2+, the plateau phase of the action potential disappears and no more mechanical activity can be detected. In aggregates, therefore, apparently both the fast sodium inward current and a slow inward current, which is at least partly carried by Ca2+ ions, contribute to the action potential. Pacemaker activity in spontaneously active aggregates is enhanced by adrenaline and slowed down by acetylcholine. Adrenaline also increases the plateau phase amplitude of the action potential and thereby the rate of repolarization. Acetylcholine shortens the action potential duration and increases the resting membrane potential. The electrical coupling between the cells in the aggregates is so tight that the aggregate seems to behave passively, like a single cell. It is concluded that aggregates of collagenase-dissociated neonatal rat heart cells may be used to study active electrical properties using the voltage clamp technique.