Short term exercise training and potassium channel regulation of myogenic tone in skeletal muscle

Abstract

The effect of exercise training on K+ channel regulation of myogenic tone in locomotory skeletal muscle is unknown. The purpose of this study was to determine whether short term exercise training (STEx) altered the contribution of various K+ channels to the regulation of vascular tone in rat soleus feed arteries (SFA). Male Sprague-Dawley rats ran on a motorized treadmill for four weeks (30 m/min, 10% grade, 60 min/d, 5 d/wk) or were confined to cages (SED). SFA were isolated and cannulated with two glass micropipettes for in vitro videomicroscopic observation, and pressurized at 90 cmH20. Development of myogenic tone did not differ between groups (SED 38.7 ± 0.6% vs. STEx 33.1 ± 0.7%). Constriction followed inhibition of calcium activated K+ channels (KCa) with either 1 mM TEA (26.3 ± 2.1 um; p=0.06) or 100 nM iberiotoxin (21.7 ± 2.1 um; p=0.07) in SFA from SED. Inhibition of KCa in SFA from STEx with either blocker did not cause constriction. Inhibition of KV with 4-aminopyridine caused similar constriction in both groups (SED 26.4 ± 2.2 um vs. STEx 33.0 ± 2.6 um). Inhibition of inward rectifier K+ channels with 30 uM BaCl2 (SED 10.8 ± 1.8 um vs. STEx 6.0 ± 3.0 um) or of the Na/K ATPase with 100 uM ouabain (SED 0.0 ± 2.9 um vs. STEx 13.1 ± 3.6 um) did not cause significant constriction in either group. Combined blockade with BaCl2 and ouabain caused significant constriction (SED 49.5 ± 3.6 um vs. STEx 61.0 ± 4.2 um) that did not differ between groups. These data indicate that KCa, KV, KIR, and the Na/K ATPase all contribute to regulation of myogenic tone in SFA, and that KCa regulation of tone is reduced by STEx.