Block of outward current in cardiac Purkinje fibers by injection of quaternary ammonium ions.

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Abstract
The effects of iontophoretic injection of the quaternary ammonium compounds tetraethylammonium (TEA) and tetrabutylammonium (TBA) in cardiac Purkinje fibers to calves were studied. TBA+ is a more effective blocker than TEA+, but injection of either compound reduces the time-dependent outward plateau currents, transient outward current (Ito) and the delayed rectifier (Ix). These outward cardiac currents are carried by channels that in some respects are pharmacologically similar to squid axon K channels. This procedure is a new tool that can be useful in the analysis of membrane currents in the heart.