Effects of anion exchange on intracellular pH and tension in basilar artery of dogs.

We simultaneously measured intracellular pH (pHi) and isometric tension in canine basilar arteries. pHi was calculated from the ratio of fluorescence intensities at 540 nm of exciting wavelengths of 500 and 440 nm in the presence of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). pHi was 7.33 +/- 0.02 in Krebs-Henseleit solution (pH of 7.4 at 37 degrees C). Application of the anion exchange blocker 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) decreased the resting pHi by 0.25 pH units. Increasing extracellular pH (pHo) [by decreasing CO2 tension (PCO2)] from 7.4 to 7.8 increased pHi by 0.38 pH units and increased tension by 2.28 +/- 0.21 mN. Decreasing pHo from 7.8 to 7.4 (by increasing PCO2) restored the pHi and muscle tension to their baseline levels. SITS inhibited the increase in pHi and isometric tension in response to the increase in pHo in an endothelium-independent fashion. The Na+/H+ exchange blockers, amiloride or 5-(N-methyl-N-guanidinocarbonylmethyl)-amiloride, did not affect the pHo or tension changes. The results suggest that in the range of pH tested, anion exchange is more important than Na+/H+ exchange in the regulation of pHi and mechanical tone in the basilar artery.