All cells have the recovery mechanisms from the shift of intracellular pH (pH_i). Many mechanisms were found and characterized. In cardiac myocytes, two Cl^–-dependent mechanisms were responsible for the recovery from alkalosis, such as Cl^–-OH^– exchange and Cl^–-HCO₃^– exchange (Leem & Vaughan-Jones, 1998). In mesenteric arteriole, it is still not unclear which mechanisms are responsible for the alkaline recovery (Aalkjaer & Hughes, 1991). In this report, we would like to characterize the alkaline recovery mechanisms in vascular smooth muscle.

We humanely killed rats with ketamine (100 mg kg^-1) and removed mesenteric vascular beds. We isolated the 4th branch mesenteric arteriole (< 150 µm) and loaded carboxy SNARF-1 to measure pH_i change (Leem & Vaughan-Jones, 1998). To induce alkalosis, we used the acetate pre-pulse technique or CO₂-removal technique. In HCO₃^–-free Hepes-buffered conditions or CO₂/HCO₃^–-buffered conditions, the pH_i recovered from induced alkalosis. The calculated proton flux in the CO₂/HCO₃^–-buffered conditions was larger than that in HCO₃^–-free Hepes-buffered conditions. This recovery was completely inhibited by the removal of extracellular Cl^– (Clä{special}) which was replaced by glucuronic acid. 4,4â-Diiisothiocyanatostilbene-2,2â-disulfonic acid (DIDS, 500 µM), a classical blocker of the Cl^–-HCO₃^– exchanger, did not inhibit the alkaline recovery in HCO₃^–-free Hepes-buffered conditions or CO₂/HCO₃^–-buffered conditions. The other stilbene drugs such as 4-acetamido-4â-isothio-cyanatostilbene-2,2â-disulfonic acid (SITS) or dibenzamidostilbene-disulphonic acid (DBDS) also had no effect on the recovery. In CO₂/HCO₃-buffered conditions, the removal of extracellular Na⁺ (Na¬{special}), which was replaced by N-methyl-D-glucamine (NMDG), greatly accelerated the recovery (at pH_i = 7.15, -0.007 ± 0.001 pH min^-1 vs. -0.051 ± 0.008 pH min^-1, mean ± S.E.M., n = 3, P < 0.05, Student’s paired t test). When K⁺ or Cs⁺ were substituted for Na¬{special}, the recovery was slightly accelerated but was greatly attenuated compared to NMDG substitution (K⁺ substitution, at pH_i = 7.15, -0.015 ± 0.001 pH min^-1, mean ± S.E.M., n = 3).

These results suggest that in arteriolar smooth muscle, a novel Cl^–-dependent and HCO₃^–-dependent or -independent mechanism was responsible for the recovery from alkalosis. This mechanism was not sensitive to stilbene derivatives and affected by monovalent cations such as Na⁺, K⁺ or Cs⁺ in the presence of HCO₃^–. Still we do not know the exact stoichiometry of this mechanism and it is necessary to perform further studies to identify the characteristics.

This work was supported by grant No. IMT2000-C3-3 (Advanced Backbone IT Technology Development Project) from Ministry of Information and Communication.