Effects of cryptand 2.2.1Py on the fast sodium current in cardiac Purkinje fibers.

For study of dose-dependent influence on sodium current, sheep heart Purkinje fibers were perfused with a cryptand (2.2.1Py) and measured for resting potential, overshoot, amplitude and duration of action potential, refractory period, and rate of rise. Concomitant investigation was made by voltage clamp. The cryptand was found to depress maximal rate rise with increase of concentration and induce shift toward negative potential with increase of dose. Also, effect on sodium current kinetics was observed but not on resting potential. The findings indicate that 2.2.1Py action probably is not primarily ionophores, negating the idea that cryptands promote transmembrane ion exchange.