IP₃R-TRPM4 Coupling Determines the Spatial Reach of Pericyte-Mediated Capillary Constriction

Ensheathing pericytes extend multiple projections that wrap around capillary vessels to regulate diameter and direct blood flow distribution across the microvascular network. At capillary bifurcations, individual projections wrap around branches of different diameters, positioning the pericyte to simultaneously regulate multiple vessel segments. Using optogenetic tools in acta2-opto-α1AR and acta2-CatCh mice, we show that Gq-coupled receptor activation confines contractile responses to the projection receiving the stimulus, whereas direct membrane depolarization propagates to projections wrapping neighboring capillary branches via gap junction-independent mechanisms. Computational modeling revealed that TRPM4, a Ca²⁺-activated nonselective cation channel, uniquely couples local Ca²⁺ signals to voltage-gated Ca²⁺ channel activation in projections on neighboring branches at physiologically relevant channel abundances. Ca²⁺ imaging identified two kinetically distinct event populations: slow, low-amplitude IP₃R-mediated events and fast, high-amplitude VGCC-mediated transients. Sustained low-amplitude signals selectively maintained TRPM4 activation and enabled cross-projection propagation, whereas brief high-amplitude transients drove rapid channel inactivation. Proximity ligation assays confirmed nanoscale colocalization of TRPM4 and IP₃ receptors in pericytes. Focal IP₃ photolysis produced constriction across projections wrapping multiple capillary branches that was abolished by TRPM4 blockade and enhanced by PKC-mediated augmentation of TRPM4 expression. These findings identify an IP₃R-TRPM4 signaling axis as a molecular switch that gates whether capillary constriction remains branch-specific or coordinates across the pericyte, enabling precise stimulus-dependent control of blood flow distribution in the microvasculature.