CLONING AND CHARACTERIZATION OF A K(V)1.5 DELAYED RECTIFIER K+ CHANNEL FROM VASCULAR AND VISCERAL SMOOTH MUSCLES

We have cloned and characterized the expression of a K(v)1.5 K+ channel (cK(v)1.5) from canine colonic smooth muscle. The amino acid sequence displayed a high level of identity to other K+ channels of the K(v)1.5 class in the core region between transmembrane segments S1-S6; however, identity decreased to between 74 and 82% in the NH2 and COOH terminal segments, suggesting that cK(v)1.5 is a distinct isoform of the K(v)1.5 class. Functional expression of cK(v)1.5 in oocytes demonstrated a channel highly selective for K+, which activates in a voltage-dependent manner on depolarization to membrane potentials positive to -40 mV. At room temperature the channel showed fast activation (time to half of peak current, 5.5 ms) and slow inactivation that was incomplete after 20-s depolarizations. Single channel analysis of the channel expressed in oocytes displayed a linear current-voltage curve and had a slope conductance of 9.8 +/- 1.1 pS. Northern blot analysis demonstrated differential expression of cK(v)1.5 in smooth muscles of the gastrointestinal tract and abundant expression in several vascular smooth muscles. We propose that cK(v)1.5 represents a component of the delayed rectifier current in both vascular and visceral smooth muscles.