Vol. 289, Issue 3, 1517-1522, June 1999

Peptidyl Inhibitors of Shaker-Type K_v1 Channels Elicit Twitches in Guinea Pig Ileum by Blocking K_v1.1 at Enteric Nervous System and Enhancing Acetylcholine Release

Guilherme Suarez-Kurtz¹ , Rosane Vianna-Jorge, Bianca F. Pereira² , Maria Luisa Garcia and Gregory J. Kaczorowski

Coordenação de Pesquisa, Instituto Nacional de Câncer (G.S.K.), and Departamentos de Bioquímica (G.S.K., B.F.P.) e Farmacologia (R.V.J.), Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; and Department of Membrane Biochemistry and Biophysics (M.L.G., G.J.K.), Merck Research Laboratories, Rahway, New Jersey

Potent and selective peptidyl blockers of the Shaker-type (K_v1) voltage-gated potassium channels were used to determine the role of these channels in regulating the spontaneous motility of smooth muscle preparations. Margatoxin (MgTX), kaliotoxin, and agitoxin-2 at 1 to 10 nM and agitoxin-1 at 50 to 100 nM induce twitches in guinea pig ileum strips. These twitches are abolished by tetrodotoxin (TTX, 0.5 µM), atropine (1 µM), hexamethonium (10 µM), or nifedipine (0.1 µM). It is proposed that blockade of K_v1 channels by MgTX, kaliotoxin, or the agitoxins increases excitability of intramural nerve plexuses in the ileum, promoting release of acetylcholine from excitatory motor nerve terminals. This, in turn, leads to Ca²⁺-dependent action potentials and twitching of the muscle fibers. MgTX does not induce twitches in several other guinea pig and/or rat vascular, genitourinary, or gastrointestinal smooth muscles, although small increases in spontaneous myogenic activity may be seen in detrusor muscle exposed to >30 nM MgTX. This effect is not reversed by TTX or atropine. The TTX- and atropine-sensitive twitches of guinea pig ileum are also induced by nanomolar concentrations of -dendrotoxin, a selective blocker of Shaker K_v1.1 and 1.2 subtypes, or stichodactylatoxin, a peptide isolated from sea anemone that displays high affinity for K_v1.1 and 1.3, but not by charybdotoxin, which blocks K_v1.2 and 1.3 but not 1.1. The data taken together suggest that high-affinity blockade of K_v1.1 underlies the ability of MgTX, kaliotoxin, agitoxin-1, agitoxin-2, -dendrotoxin, and stichodactylatoxin to elicit TTX-sensitive twitches in guinea pig ileum.