Cloning and expression of a Kv1.2 class delayed rectifier K+ channel from canine colonic smooth muscle (original) (raw)

1993, Proceedings of the National Academy of Sciences

A cDNA (CSMK1) encoding a delayed rectifier K+ channel of the K,1.2 dass was cloned from canine colonic circular smooth muscle and expressed in Xenopus oocytes. These channels appear to be uniquely expressed in gastrointestinal muscles and may participate in the electrical slow wave activity. Functional expression of CSMK1 in Xenopus oocytes demonstrated a K+ current that activated in a voltage-dependent manner upon depolarization. This current was highly sensitive to 4-aminopyridine (IC5o, 74 pM). A low-conductance K+ channel was identified in inside-out patches from oocytes iDiected with CSMK1. This channel displayed a linear current-voltage relation with a slope conductance of 14 pS. The channels were blocked in a concentration-dependent manner by 4-aminopyridine. Northern blot analysis demonstrated that CSMK1 is expressed in a wide variety of gastrointestinal smooth muscles. Portal vein, renal artery, and uterus do not express CSMK1, suggesting that, among smooth muscles, expression of this K* channel may be restricted to gastrointestinal smooth muscles. CSMK1 is 91% homologous to RAK, a delayed rectifier K+ channel cloned from rat heart, but displays unique pharmacological properties and tissue distribution. The contractile behavior of smooth muscles depends to a considerable extent upon the electrical activities of these muscles. Electrical activity can vary from a tonic membrane potential that changes slowly in response to regulatory substances to fast Ca2+ action potentials that occur in response to excitatory agonists. Gastrointestinal (GI) smooth muscles exhibit the complete range of electrical events, and the cause of this diversity has been a central question of investigation for at least 50 years. Prevalent in the electrical repertoire of GI muscles is the activity known as electrical slow waves (1-4). The major ionic currents that appear to be responsible for these events have been reviewed (5). K+ channels found in GI smooth muscles include Ca2+-activated K+ channels (e.g., ref. 6), delayed rectifiers (e.g., refs. 7 and 8), inward rectifiers (e.g., ref. 9), and a lemakalim-sensitive conductance that may be an ATP-sensitive K+ channel (10). Among these currents, de