Role of age, Rho-kinase 2 expression, and G protein-mediated signaling in the myogenic response in mouse small mesenteric arteries

The myogenic response (MR) and myogenic tone (MT) in resistance vessels is crucial for maintaining peripheral vascular resistance and blood flow autoregulation. Development of MT involves G protein-coupled receptors, and may be affected by aging. Aims: (1) to estimate the mesenteric blood flow in myogenically active small mesenteric arteries; (2) to investigate the signaling from G(alpha q/11) and/or G(alpha 12) activation to MT development; (3) to investigate the role of Rho-kinase 2 and aging on MT in mesenteric resistance arteries. Methods: we used pressure myography, quantitative real-time PCR, and immunolocalization to study small (<200 mu m) mesenteric arteries (SMA) from young, mature adult, and middle aged mice. Results: Poiseuille flow calculations indicated autoregulation of blood flow at 60-120 mm Hg arterial pressure. G(alpha q/11) and Gexpression/activity(12) were abundantly expressed at the mRNA and protein levels in SMA. The G(alpha q/11) inhibitor YM-254890 suppressed MT development, and the Phosholipase C inhibitors U73122 and ET-18-OCH3 robustly inhibited it. We found an age-dependent increase in ROCK2 mRNA expression, and in basal MT. The specific ROCK2 inhibitor KD025 robustly inhibited MT in SMAs in all mice with an age-dependent variation in KD025 sensitivity. The inhibitory effect of KD025 was not prevented by the L-type Ca2+ channel activator BayK 8644. KD025 reversibly inhibited MT and endothelin-1 vasoconstriction in small pial arteries from Gottingen minipigs. Conclusions: MT development in SMAs occurs through a G(alpha q/11)/PLC/Ca2+-dependent pathway, and is maintained via ROCK2-mediated Ca2+ sensitization. Increased MT at mature adulthood can be explained by increased ROCK2 expression/activity.