EFFECTS OF A SHAKER K+ CHANNEL PEPTIDE AND TRYPSIN ON A K+ CHANNEL INNECTURUS ENTEROCYTES

We have previously demonstrated that a synthetic peptide composed of t he first 22 amino acids from the NH2-terminus of the Shaker B K+ chann el protein deactivates a voltage-dependent K+ channel present in basol ateral membrane of Necturus small intestinal epithelial cells reconsti tuted into planar lipid bilayers (Dubinsky et al. Proc. Natl. Acad. Sc i. USA 89: 1770-1774, 1992). We now demonstrate that this peptide inte racts with the inner surface of the Necturus channel only when it is i n the open or conducting configuration and that this interaction is hi ndered by tetraethylammonium ion, a well-established blocker of this a nd other K+ channels. We conclude that this peptide is an open-pore bl ocker of the Necturus K+ channel as it appears to be in the case of th e Shaker B K+ channel. We further demonstrate that trypsin, which abol ishes the ability of this peptide to block both the Necturus and the S haker 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, sugges t structural homologies between the 'inactivation peptide'' of the Sha ker B K+ channel and the voltage-gate of the Necturus K+ channel.