pH gradient effects on chloride transport across basolateral membrane vesicles from guinea-pig jejunum
1. The effects of alkaline-inside pH gradients on 36Cl- uptake were quantified by using brush-border membrane (BBM) and basolateral membrane (BLM) vesicles from guinea-pig jejunum. 2. With BBM vesicles, a pHo/pHi gradient of 5.0/7.5 yielded fast overshoots involving a random, non-obligatory Cl(-)-H+...
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Veröffentlicht in: | The Journal of physiology 1997-04, Vol.500 (Pt 2), p.385-400 |
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Zusammenfassung: | 1. The effects of alkaline-inside pH gradients on 36Cl- uptake were quantified by using brush-border membrane (BBM) and basolateral
membrane (BLM) vesicles from guinea-pig jejunum. 2. With BBM vesicles, a pHo/pHi gradient of 5.0/7.5 yielded fast overshoots
involving a random, non-obligatory Cl(-)-H+ symport, strongly inhibited by CCCP. In contrast, BLM vesicles responded to similar
pH gradients with much smaller, delayed overshoots, unaffected by CCCP. 3. The initial Cl- entry rates into BLM vesicles were
a function of each pHo, pHi and delta pH value. They were stimulated by valinomycin in the presence of inward-directed K+
gradients. Short-circuiting the membrane potential with equilibrated K+ and valinomycin inhibited pH gradient-dependent Cl-
uptake, but only partially. 4. Taken together, these results indicate that guinea-pig jejunal BLM vesicles possess both Cl-
conductance and Cl(-)-H+ symport activities. 5. Even when different, the BBM and the BLM symporters are mechanistically similar.
Neither of them involves a Cl(-)-OH- antiport, nor a simultaneous Cl(-)-anion exchange mechanism. Rather, for each membrane,
all of these activities (symport, anion exchange) can be explained in terms of a single mobile carrier acting as a random,
non-obligatory Cl(-)-H+ symporter where exchange occurs simply by counterflow. Net Cl- translocation via either the ternary
(Cl(-)-C-H+) or the binary (Cl(-)-C) complexes accounts, respectively, for the existence of two, operationally distinct, electroneutral
and rheogenic components. 6. The BBM symporter appears to involve an AE2 protein, but the molecular identity of the BLM one
remains to be established. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.1997.sp022029 |