Intravascular Pressure Augments Cerebral Arterial Constriction by Inducing Voltage‐Insensitive Ca2+ Waves

Abstract

This study examined whether elevated intravascular pressure stimulates asynchronous Ca2+ waves and if their generation contributes to myogenic tone development. Rat cerebral arteries were mounted in an arteriograph, pressurized (20–100 mmHg) and examined under a variety of experimental conditions. Diameter and membrane potential (VM) were monitored using conventional techniques; Ca2+ wave generation and myosin light chain (MLC20)/MYPT1 phosphorylation were assessed by confocal microscopy and western blot analysis, respectively. Elevating intravascular pressure increased the proportion of smooth muscle cells firing Ca2+ waves as well as event frequency. Ca2+ wave augmentation occurred primarily at lower intravascular pressures and ryanodine, an agent that depletes the sarcoplasmic reticulum (SR), eliminated these events. Ca2+ wave generation was voltage‐insensitive as Ca2+ channel blockade and perturbations in extracellular [K+] had little effect on measured parameters. Ryanodine‐induced inhibition of Ca2+ waves attenuated myogenic tone and MLC20 phosphorylation without altering arterial VM. Thapsigargin also attenuated Ca2+ waves, pressure‐induced constriction and MLC20 phosphorylation. The SR‐driven component of the myogenic response was proportionally greater at lower intravascular pressures and subsequent MYPT1 phosphorylation measures revealed that SR Ca2+ waves facilitate pressure‐induced MLC20 phosphorylation through mechanisms that include myosin light chain phosphatase inhibition. Our findings show that mechanical stimuli augment Ca2+ wave generation and that these transient events facilitate tone development particularly at lower intravascular pressures by providing a proportion of the Ca2+ required to directly control MLC20 phosphorylation.