AJP - Cell Physiology, Vol 265, Issue 2 C541-C547, Copyright © 1993 by American Physiological Society
Effects of a Shaker K+ channel peptide and trypsin on a K+ channel in Necturus enterocytes
O. Mayorga-Wark, J. Costantin, W. P. Dubinsky and S. G. Schultz
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
We have previously demonstrated that a synthetic peptide composed of the
first 22 amino acids from the NH2-terminus of the Shaker B K+ channel
protein deactivates a voltage-dependent K+ channel present in basolateral
membrane of Necturus small intestinal epithelial cells reconstituted into
planar lipid bilayers (Dubinsky et al. Proc. Natl. Acad. Sci. USA 89:
1770-1774, 1992). We now demonstrate that this peptide interacts with the
inner surface of the Necturus channel only when it is in the open or
conducting configuration and that this interaction is hindered by
tetraethylammonium ion, a well-established blocker of this and other K+
channels. We conclude that this peptide is an open-pore blocker of the
Necturus K+ channel as it appears to be in the case of the Shaker B K+
channel. We further demonstrate that trypsin, which abolishes the ability
of this peptide to block both the Necturus and the Shaker K+ channels and
inhibits spontaneous inactivation of the Shaker K+ channel, also impairs
the voltage-gate of the Necturus K+ channel. These findings, and others to
be reported in a companion paper, suggest structural homologies between the
"inactivation peptide" of the Shaker B K+ channel and the voltage-gate of
the Necturus K+ channel.
