Abstract
4-AP, applied in quantities varying from 0.1 to 0.5 mM, is known to selectively abolish the majority of the early outward current, iqr , activated in sheep cardiac Purkinje fibers by voltage clamp pulses positive to −30 mV. The increase in action potential duration, the depolarization of the resting potential, and the induction of spontaneous activity by 1 to 5 mM 4-AP indicate that this drug also affects membrane currents responsible for the electrical behavior of this preparation at more negative potentials. This chapter describes a study to examine the effects of 4-aminopyridine (4-AP) on membrane currents in the pace-maker voltage range of sheep cardiac purkinje fibers. This was investigated with the voltage-clamp technique using two intracellular micro-electrodes in short sheep Purkinje strands. It is found that with 5 mM 4-AP added to a normal solution, buffered at pH 7.4 with 20 mM HEPES, the steady-state current-voltage relation flattens and loses its typical N-shape. The time-dependent current, responsible for the pacemaker activity is reduced in amplitude, and its voltage dependency is shifted 16 + 2.2 mV toward less negative potentials.
Published Version
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