Characterization of 4-aminopyridine block of the non-inactivating
cloned k+ channel, kv 1.5, expressed in xenopus oocytes.
Yamane, Teiichi, Tetsushi Furukawa, and Masayasu Hiraoka.
Department of Cardiovascular Diseases and Autonomic Physiology,
Medical Research Institute, Tokyo Medical and Dental University, 1-5
-45, Yushima, Bunkyo-ku, Tokyo 113, Japan
APStracts 2:0105H, 1995.
The blocking action of 4-aminopyridine (4-AP) on the cloned K+
channel, Kv1.5, expressed in Xenopus oocytes was studied using the
two-microelectrode voltage clamp method. Application of 4-AP to the
bath solution reversibly suppressed the expressed current in a
voltage- and concentration-dependent manner decreasing with membrane
depolarization and with IC50=0.14 mM (at +40 mV). Both block and
unblock occurred mainly during a depolarization when channels were
activated. With successive depolarizations, 4-AP decreased not only
the peak amplitudes of the current in successive pulses, but also the
current during a depolarization. Upon wash out of 4-AP, the current
recovered with successive depolarizations, while no recovery of the
current was noted in the absence of depolarizations. The extent of
block markedly increased with alkalization of the external solution
and decreased with acidification. External application of 4-APMI, a
charged form of a quaternary 4-AP derivative, did not affect the
current, but internal application markedly suppressed the current,
indicating the drug gained access to the channel from cytoplasmic
side. These data suggest that 4-AP crosses the membrane in its
uncharged form and acts from inside of the cell in its charged form,
resulting in block of the channels with higher affinity to the open
state.
Received 12 August 1994; accepted in final form 2 March 1995.
APS Manuscript Number H728-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.