Increased amplitude of inward rectifier K + currents with advanced age in smooth muscle cells of murine superior epigastric arteries.

Inward rectifier K ⁺ channels (K _IR ) may contribute to skeletal muscle blood flow regulation and adapt to advanced age. Using mouse abdominal wall superior epigastric arteries (SEAs) from either young (3-6 mo) or old (24-26 mo) male C57BL/6 mice, we investigated whether SEA smooth muscle cells (SMCs) express functional K _IR channels and how aging may affect K _IR function. Freshly dissected SEAs were either enzymatically dissociated to isolate SMCs for electrophysiological recording (perforated patch) and mRNA expression or used intact for pressure myography. With 5 mM extracellular K ⁺ concentration ([K ⁺ ] _o ), exposure of SMCs to the K _IR blocker Ba ²⁺ (100 μM) had no significant effect ( P > 0.05) on whole cell currents elicited by membrane potentials spanning -120 to -30 mV. Raising [K ⁺ ] _o to 15 mM activated Ba ²⁺ -sensitive K _IR currents between -120 and -30 mV, which were greater in SMCs from old mice than in SMCs from young mice ( P < 0.05). Pressure myography of SEAs revealed that while aging decreased maximum vessel diameter by ~8% ( P < 0.05), it had no significant effect on resting diameter, myogenic tone, dilation to 15 mM [K ⁺ ] _o , Ba ²⁺ -induced constriction in 5 mM [K ⁺ ] _o , or constriction induced by 15 mM [K ⁺ ] _o in the presence of Ba ²⁺ ( P > 0.05). Quantitative RT-PCR revealed SMC expression of K _IR 2.1 and K _IR 2.2 mRNA that was not affected by age. Barium-induced constriction of SEAs from young and old mice suggests an integral role for K _IR in regulating resting membrane potential and vasomotor tone. Increased functional expression of K _IR channels during advanced age may compensate for other age-related changes in SEA function. NEW & NOTEWORTHY Ion channels are integral to blood flow regulation. We found greater functional expression of inward rectifying K ⁺ channels in smooth muscle cells of resistance arteries of mouse skeletal muscle with advanced age. This adaptation to aging may contribute to the maintenance of vasomotor tone and blood flow regulation during exercise.
(Copyright © 2017 the American Physiological Society.)