Role of Potassium Channel Function and Long‐term Exercise Training in Soleus Resistance Arterioles

Abstract

IntroductionNuclear factor (erythroid‐derived 2)‐like 2 (Nrf2) expression has been linked to potassium (K+) channel function. We hypothesized that myogenic responses are enhanced by exercise training and also modulated by K+ channel function but would be impaired in arterioles from skeletal muscle of trained rats in which Nrf2 (Nrf2 KO) is deleted.MethodsExercise training was performed in male wildtype (WT) Sprague‐Dawley rats, and their littermates lacking the Nrf2 gene (Nrf2 KO). Rats were exercise trained using a mixed moderate and high‐intensity interval treadmill program for 10‐12 weeks. A WT cage‐confined control group was also studied to compare the impact of exercise training. After exercise training or sedentary cage‐confinement, soleus resistance arterioles were isolated and cannulated for the assessment of vascular reactivity. Vasodilatory responses to low concentrations of KCl [10 and 20mM} were assessed. Vasoconstrictor responses to higher concentrations of KCl [30–100mM] and myogenic responses to increasing intraluminal pressure (pressure 0cm H2O – 130cm H2O) were also assessed. The contribution of inward rectifying K+ channels (Kir) to vasodilation during low concentrations of KCl was assessed by treatment with barium chloride (BaCl2, 100mM).ResultsSoleus resistance arteriole myogenic responsiveness was reduced in trained Nrf2 KO as compared to WT (p<0.01). Trained WT rats produced a significantly higher myogenic responsiveness than sedentary WT controls (p<0.05). Vasodilation to low concentrations of KCl was reduced in soleus arterioles from trained Nrf2 KO rats as compared to arterioles from trained WT rats (p<0.01). Exercise training did not alter vasodilation to low KCl concentrations in WT rats (p>0.05). Constriction to higher concentrations of KCl was similar in arterioles from trained WT and Nrf2 KO rats. Inhibiting Kir channels with BaCl2 eliminated the genotype‐ and training‐related differences in myogenic responses and vasodilation to KCl.ConclusionOur data indicate that Nrf2 may be a critical regulator of vascular adaptation that occurs in skeletal muscle arterioles in response to long‐term exercise training. Elimination of differences in myogenic responsiveness by BaCl2 suggest that Nrf2‐mediated adaptation of the myogenic responsiveness may involve Kir channels.