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55 POTASSIUM CHANNEL REGULATION OF VASCULAR TONE.
  1. K. Onishi1,
  2. S. Achanti2,
  3. J. L. Jasperse2
  1. 1Western University of Health Sciences, College of Osteopathic Medicine of the Pacific, Pomona, CA
  2. 2Department of Sports Medicine, Pepperdine University, Malibu, CA.

Abstract

Pressurized arteries develop active resting tone that is endothelium independent and appears to result from activation of stretch-activated Ca++ channels and voltage-gated Ca++ channels. In cerebral and coronary arteries, activation of Ca++-activated K+ channels (KCa) and voltage-dependent K+ channels (KV) acts as a negative feedback mechanism to limit Ca++-induced depolarization and contraction. The role of K+ channels in regulating resting tone in skeletal muscle resistance arteries is not known. Therefore, we tested the hypothesis that KCa, KV, inward rectifier K+ channels (KIR), and the Na+-K+ pump contribute to regulation of resting tone in soleus feed arteries (SFAs). SFAs from male Sprague-Dawley rats were isolated and cannulated with two glass micropipettes for in vitro videomicroscopic observation, and pressurized at 90 cmH2O. After development of resting tone (35.7 ± 0.5%), various blockers of K+ channels were applied in randomized order to determine the effect of specific K+ channels on resting tone. Inhibition of KCa with either tetraethylammonium (1 mM) or iberiotoxin (10 nM) did not significantly alter resting tone. Inhibition of KV with 4-aminopyridine (1 mM) also did not alter resting tone, although there was a tendency for tone to be enhanced by Kv inhibition (diameter 129.7 ± 2.6 vs 106.1 ± 2.1 μm; p = .07). Inhibition of KIR with barium chloride (30 μM) did not alter resting tone nor did inhibition of the Na+-K+ pump with ouabain (100 μM). However, combined inhibition of KIR and the Na+-K+ pump significantly increased resting tone (diameter 164.7 ± 9.7 vs 108.3 ± 10.2 μm). These data indicate that but KV, KIR, and the Na+-K+ pump each contribute to regulation of resting tone in SFAs. Unlike cerebral and coronary arteries, KCa channels do not significantly regulate tone in SFAs. These data suggest that these K+ channels are important contributors to the regulation of blood flow in skeletal muscle.

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