Endothelial K_IR2 channel dysfunction in aged cerebral parenchymal arterioles

Aging is associated with cognitive decline via incompletely understood mechanisms. Cerebral microvascular dysfunction occurs in aging, particularly impaired endothelium-mediated dilation. Parenchymal arterioles are bottlenecks of the cerebral microcirculation, and dysfunction causes a mismatch in nutrient demand and delivery, leaving neurons at risk. Extracellular nucleotides elicit parenchymal arteriole dilation by activating endothelial purinergic receptors (P2Y), leading to opening of K⁺ channels, including inwardly-rectifying K⁺ channels (K_IR2). These channels amplify hyperpolarizing signals, resulting in dilation. However, it remains unknown if endothelial P2Y and K_IR2 signaling are altered in brain parenchymal arterioles during aging. We hypothesized that aging impairs endothelial P2Y and K_IR2 function in parenchymal arterioles. We observed reduced dilation to the purinergic agonist 2-methyl-S-ADP (1 µM) in arterioles from Aged (>24-month-old) mice when compared to Young (4-6 months of age) despite similar hyperpolarization in endothelial cells tubes. No differences were observed in vasodilation or endothelial cell hyperpolarization to activation of small- and intermediate-conductance Ca²⁺-activated K⁺ channels (K_Ca2.3 / K_Ca3.1) by NS309. Hyperpolarization to 15 mM [K⁺]_E was smaller in Aged than Young mice, despite a paradoxical increased dilation in Aged arterioles to 15 mM [K⁺]_E that was unchanged by endothelium removal. K_IR2 Inhibition attenuated vasodilatory responses to 15 mM [K⁺]_E and 1 µM 2-me-S-ADP in both Young and Aged arterioles. Further, we observed a significant increase in myogenic tone in Aged parenchymal arterioles, which was not enhanced by endothelium removal. We conclude that aging impairs endothelial K_IR2 channel function in the cerebral microcirculation with possible compensation by smooth muscle cells.