Motor responses of cultured rat cerebral vascular smooth muscle cells to intra- and extracellular pH changes

Alkalizing perivascular fluid constricts, whereas acidification dilates, cerebral arterioles. It is not known whether vascular smooth muscle cells (VSMCs), endothelium, or neuronal elements sense pH changes. We hypothesized that VSMCs themselves transduce extracellular pH (pH(0)) changes. We examined the motor responses of cultured adult rat middle cerebral arterial VSMCs during pH, and intracellular pH (pH(i)) changes. Motor responses were inferred from the deformation pattern of a silicons substratum, dimethylpolysiloxane, which wrinkles as cells contract. pH(i) was measured with 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. Cultured VSMCs retained motor responses to vasoconstrictors (5-hydroxytryptamine and K+), and to sodium nitroprusside, which were typical of intact arterioles. VSMCs contracted with increasing and relaxed with decreasing pH(0). Hypocapnia contracted VSMCs when the pH(0) increased, and hypercapnia relaxed VSMCs when the pH(0) decreased. However, at a constant pH(0), changes in PCO2 caused opposite responses despite equivalent changes in pH(i). Thus VSMCs contract with increased pH(0) and relax with decreased pH(0) just as intact arterioles do. These responses do not reflect changes in pH(i) or PCO2. pH(i) changes paradoxically alter VSMC tone in the direction opposite that caused by pH(0) changes.