EFFECTS OF ANION-EXCHANGE ON INTRACELLULAR PH AND TENSION IN BASILAR ARTERY OF DOGS

We simultaneously measured intracellular pH (pH(i)) and isometric tens ion in canine basilar arteries. pH(i) 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)-carboxyfluores cein (BCECF), pH(i) was 7.33 +/- 0.02 in Krebs-Henseleit solution (pH of 7.4 at 37 degrees C). Application of the anion exchange blocker -ac etamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) decreased the resting pH(i) by 0.25 pH units. Increasing extracellular PH (pH(0) ) [by decreasing CO2 tension (PCO2)] horn 7.4 to 7.8 increased pH(i) b y 0.38 pH units and increased tension by 2.28 +/- 0.21 mN, Decreasing pH(0) from 7.8 to 7.4 (by increasing PCO2) restored the pH(i) and musc le tension to their baseline levels. SITS inhibited the increase in pH (i) and isometric tension in response to the increase in pH(0) in an e ndothelium-independent fashion, The Na+/H+ exchange blockers, amilorid e or 5-(N-methyl-N-guanidinocarbonylmethyl)-amiloride, did not affect the pH(0) or tension changes. The results suggest that in the range of PH tested, anion exchange is more important than Na+/H+ exchange in t he regulation of pH(i) and mechanical tone in the basilar artery.