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Juvenile growth reduces the influence of epithelial sodium channels on arteriolar tone

Juvenile growth can be accompanied by a change in the myogenic behavior of arterioles. In renal arterioles, myogenic constriction depends on activation of epithelial sodium channels (ENaC). Our goal was to determine if ENaC contributes to myogenic behavior and vascular tone in arterioles outside of the kidney, and if so, whether this contribution changes during growth. Gracilis muscle arterioles from rats aged 22–26 days (weanlings) or 42–46 days (juveniles) developed spontaneous tone when pressurized in vitro. From 40–100 mm Hg, constrictor responses to stepwise pressure elevations were greater in weanling versus juvenile arterioles (0.31 ± 0.1 vs. 0.06 ± 0.13 % constriction/mm Hg). From 80–140 mm Hg, steady‐state vascular tone was also greater in weanling arterioles. Expression of ENaC subunits was similar in weanling and juvenile arterioles. The ENaC inhibitor benzamil (1μM) increased tone but did not alter myogenic responsiveness in weanling arterioles, and had no effect on either tone or myogenic responsiveness in juvenile arterioles. Nitric oxide (NO) release was relatively low in weanling arterioles, but treatment with a NO synthase inhibitor abolished the effect of benzamil in these vessels. Our findings suggest that ENaC activity does not mediate myogenic behavior in skeletal muscle arterioles, but may influence the tone of weanling vessels by altering NO release. AHA 09GRNT2250298, VCU Med. Ctr.