Inhibition of a K+ current by beta-dendrotoxin in primary and subcultured vascular smooth muscle cells.
beta-Dendrotoxin (beta-DTX), a polypeptide component of Eastern Green Mamba snake venom, inhibits a slow voltage-activated 86Rb efflux from synaptosomes, suggesting that beta-DTX inhibits K+ channels. The effects of beta-DTX on the K+ currents in primary cultured and subcultured (passages 8-12) rat tail artery vascular smooth muscle cells (VSMCs) were studied using the whole-cell patch-clamp technique. A delayed rectifier K+ current was observed in both types of cells. The current, which was relatively insensitive to tetraethylammonium, was activated at -40 to -30 mV and showed almost no inactivation. beta-DTX (1-1000 nM) decreased the outward K+ current. The effect was concentration dependent and reversible by washout but did not depend on the frequency of stimulation (use dependence) or the membrane potential. beta-DTX was more effective in primary cultured cells than in subcultured cells. K+ channels in primary cultured cells were maximally (45%) inhibited by 1 microM beta-DTX compared with 35% inhibition in subcultured cells. The concentration producing half-maximal inhibition was 5.1 x 10(-8) M for primary cells and 7.1 x 10(-8) M for subcultured cells. The delayed rectifier current was not affected by alpha-DTX, a blocker of the fast-inactivating outward K+ current (IA). These results clearly demonstrate that beta-DTX is a novel antagonist of the delayed rectifier K+ current in primary and subcultured rat tail artery VSMCs.
Ren
J
J
Department of Physiology, Faculty of Medicine, University of Alberta, Edmonton, Canada.
Karpinski
E
E
Benishin
C G
CG
D000818:Animals; D002478:Cells, Cultured; D004546:Elapid Venoms / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology*; D011188:Potassium / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013623:Tail / Q000098:blood supply
D004546:Elapid Venoms; D010455:Peptides; D015221:Potassium Channels; C081640:dendrotoxin, beta; D011188:Potassium