ISSN:
1432-1424
Keywords:
Lens pH
;
pH regulation
;
bicarbonate
;
BCECF
;
Cl−-HCO 3 -
;
exchanger
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary The intracellular pH (pH i ) of tissue-cultured bovine lens epithelial cells was measured in small groups of 6 to 10 cells using the trapped fluorescent dye 2′,7′-bis-(2-,carboxyethyl)-5 (and 6)carboxyfluorescein (BCECF). When perifused at 35°C with artificial aqueous humour solution (AAH) containing 16 mM HCO 3 - and 5% CO2, pH 7.25, pH i was 7.19±0.02 (sem, n = 95). On removing HCO 3 - and CO2 there was an initial transient alkalinization followed by a fall in pH to a steady value of 6.97±0.03 (sem, n = 54). Addition of 0.25 mM 4,4′-diisothiocyanatostilbene2, 2′-disulfonic acid (DIDS) to AAH containing HCO 3 - and CO2 led to a rapid and pronounced fall in pH. Exposure to Na+-free AAH again led to a marked fall in pH i , but in this case the addition of DIDS did not produce a further fall. Substitution of the impermeant anion gluconate for Cl− in the presence of HCO 3 - led to a rise in pH i , while substitution in the absence of HCO 3 - led to a fall in pH i . The above data indicate a significant role for a sodium-dependent Cl−-HCO 3 - exchange mechanism in the regulation of pH i . Addition of 1 mM amiloride to control AAH in both the presence and absence of HCO 3 - led to a marked fall in pH i , indicating that a Na+/H+ exchange mechanism also has a significant role in the regulation of pH i . There is evidence for a lactic acid transport mechanism in bovine lens cells, as addition of lactate to the external medium produced a rapid fall in pH i . Larger changes in pH i were observed in control compared to HCO 3 - -free AAH and in the latter case a pronounced alkalinizing overshoot was obtained on removing external lactate. Tissue-cultured bovine lens cells thus possess at least three membrane transport mechanisms that are involved in pH regulation. The buffering capacity of the lens cells was measured by perturbing pH i with either NH 4 + or procaine. The values obtained were similar in both cases and the intrinsic buffering capacity measured in the absence of external HCO 3 - was 5 mm/pH unit (procaine). However, in the presence of HCO 3 - and CO2 the buffer capacity increases approximately fourfold, indicating that HCO 3 - is the principal intracellular buffer.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00219513
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