Time- and voltage-dependent block of the delayed K+ current by quinidine in rabbit sinoatrial and atrioventricular nodes.

摘要: The modes in which quinidine blocks the delayed K+ current (IK) of rabbit sinoatrial and atrioventricular nodes were investigated by voltage clamp experiments using small preparations. Depolarizing pulses applied from a holding potential -50 mV resultant IK was evaluated. At concentration 2 x 10(-6) M, blocked 52 +/- 5% with 1000-msec test pulse 0 mV, whereas it inhibited slow inward only 5 to 10%. inhibition enhanced increasingly larger depolarizations. activation curve obtained use shifted toward hyperpolarization 3.0 its slope factor increased 7.3 8.8, suggesting voltage-dependent mechanism for blockage. Short depolarizing hardly affected II. presence did not show any delay. These results indicated low affinity closed (deactivated) channels. deactivation time constant significantly prolonged 120 145 msec at mV. By applying modulated receptor model current, tail well reconstructed when drug-channel interactions 300 2000 -30 It is suggested that unblocking slows decay current.