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 (pHo) changes. We examined the motor responses of cultured adult rat middle cerebral arterial VSMCs during pHo and intracellular pH (pHi) changes. Motor responses were inferred from the deformation pattern of a silicone substratum, dimethylpolysiloxane, which wrinkles as cells contract. pHi 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 pHo. Hypocapnia contracted VSMCs when the pHo increased, and hypercapnia relaxed VSMCs when the pHo decreased. However, at a constant pHo, changes in PCO2 caused opposite responses despite equivalent changes in pHi. Thus VSMCs contract with increased pHo and relax with decreased pHo just as intact arterioles do. These responses do not reflect changes in pHi or PCO2. pHi changes paradoxically alter VSMC tone in the direction opposite that caused by pHo changes.