Role of inward rectifier potassium channels (KIR) and the sodium‐potassium pump (Na‐K pump) in arterioles and feed arteries from rat soleus muscle

K IR and the Na‐K pump have been implicated as important mechanisms in regulating vascular tone and K‐induced dilation. We examined feed arteries (SFA), first order arterioles (1A), and second order arterioles (2A) (n=12 in each group) from the rat soleus muscle and used specific inhibitors (30 uM BaCl for K IR and 100 uM ouabain for the Na‐K pump) to determine the importance of each mechanism in the development of vascular tone and in K‐induced dilation. Male Sprague‐Dawley rats were anesthetized and SFA, 1A, and 2A were isolated, dissected free, cannulated with two glass micropipettes, and pressurized for in vitro videomicroscopic observation. Development of vascular tone was not altered by BaCl or ouabain alone in any branch order. Simultaneous application of BaCl and ouabain significantly increased tone in SFA and 1A, but not 2A. Bath replacement with isosmotic KCl (7.5–20mM) caused dilation in all three vessel types, with maximal dilation occurring at 15 mM in SFA and 12.5 mM in 1A and 2A. Maximal K‐induced dilation was greater in SFA (85 ± 2%) than in 1A (49 ± 2%) or 2A (57 ± 2%). Maximal K‐induced dilation was decreased by BaCl (43 ± 3) and BaCl + ouabain (54 ± 3) inhibited K‐induced dilation in SFA, but not in 1A or 2A. These data suggest that K is a more potent dilator of SFA than 1A or 2A and that K IR and the Na‐K pump are important mechanisms in regulating tone and dilation to potassium in SFA, but not in 1A or 2A.