Figure 2.

Selective changes in [${\text{HCO}}_3^{-}$]_o or pH_o—but not pCO₂—directly modulate basilar artery tone under OOE conditions. (a) Effects of selectively varying pH_o, [${\text{HCO}}_3^{-}$]_o or pCO₂ (maintaining other two at control levels) on VSMC pH_i in resting basilar arteries (left panel) or basilar arteries contracted by 10 µM U46619 (right panel). Under “Control” conditions, CO₂ is 5%, pH_o 7.4, and [${\text{HCO}}_3^{-}$]_o 22 mM. Compared to “Control”, “Low” refers to selective changes in CO₂ to 2.5%, [${\text{HCO}}_3^{-}$]_o to 11 mM or pH_o to 7.1, and “High” refers to selective changes in CO₂ to 10%, [${\text{HCO}}_3^{-}$]_o to 44 mM or pH_o to 7.7. Arteries are from wild-type mice (n = 6). (b) Effects of selectively varying pH_o, [${\text{HCO}}_3^{-}$]_o or pCO₂ (maintaining other two at control levels) on VSMC calculated [${\text{HCO}}_3^{-}$]_i in resting (Continued) Figure 2. Continue. basilar arteries (left panel) or basilar arteries contracted by 10 µM U46619 (right panel). Arteries are from wild-type mice (n = 6). (c-e) Effects of selectively varying pH_o, [${\text{HCO}}_3^{-}$]_o, or pCO₂ (maintaining other two at control levels) on U46619-induced tension development in basilar arteries from wild-type mice (n = 12 or 13). (f, g) Effects of selectively varying pH_o or [${\text{HCO}}_3^{-}$]_o (maintaining unvaried parameters at control levels) on U46619-induced VSMC Ca²⁺-responses in basilar arteries from wild-type mice (n = 6 for both). (h) Effects of selective changes in pH_o ([${\text{HCO}}_3^{-}$]_o=22 mM, CO₂=5%) on depolarization-induced tension development of basilar arteries from wild-type mice (n = 8). We induce depolarization by raising [K⁺]_o. (i) Effects of selective changes in pH_o ([${\text{HCO}}_3^{-}$]_o=22 mM, CO₂=5%) on depolarization-induced VSMC Ca²⁺ responses in basilar arteries from wild-type mice (n = 7). The curves in panels (c) through (i) are the results of least-squares fits to sigmoidal functions, and we compare them using extra sum-of-squares F-tests. *P < 0.05, **P < 0.01, ***P < 0.001, NS: not significantly different vs. control conditions (pH_o=7.4, [${\text{HCO}}_3^{-}$]_o=22 mM, CO₂=5%).