ISSN:
1432-1424
Keywords:
rabbit ileum
;
sulfate transport
;
sodium dependence
;
chloride dependence
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary Unidirectional fluxes of35SO4 across and into rabbit ileal epithelium were measured under short-circuit conditions, mostly at a medium SO4 concentration of 2.4mm. Unidirectional mucosa (m)-to-serosa (s) ands-to-m fluxes (J ms,J sm) were 0.456 and 0.067 μmoles hr−1 cm−2, respectively.J ms was 2.7 times higher in distal ileum than in mid-jejunum. Ouabain abolished net SO4 transport (J net) by reducingJ ms. Epinephrine, a stimulus of Cl absorption, had no effect on SO4 fluxes. Theophylline, a stimulus of Cl secretion, reducedJ ms without affectingJ sm, causing a 33% reduction inJ net. Other secretory stimuli (8-Br-cAMP, heat-stable enterotoxin, Ca-ionophore A23187) had similar effects. Replacement of all Cl with gluconate markedly reducedJ net through both a decrease inJ ms and an increase inJ sm. The anion-exchange inhibitor, 4-acetoamido-4′-isothiocyano-2,2′-sulfonic acid stilbene (SITS), when added to the serosal side, reducedJ ms by 94%, nearly abolishingJ net. SITS also decreasedJ sm by 75%. Mucosal SITS (50 μm) was ineffective. 4,4′-diisothiocyano-2,2′-sulfonic acid stilbene (DIDS) had effects similar to SITS but was less potent. Measurements of initial rates of epithelial uptake from the luminal side (J me) revealed the following: (1)J me is a saturable function of medium concentration with aV max of 0.94 μmoles hr−1 cm−2 and aK 1/2 of 1.3mm; (2) replacing all Na with choline abolishedJ me; (3) replacing all Cl with gluconate increasedJ me by 40%; (4) serosal SITS had no effect onJ me; and (5) stimuli of Cl secretion had no effect onJ me or increased it slightly. Determination of cell SO4 with35SO4 indicated that, at steady-state, the average mucosal concentration is 1.1 mmoles per liter cell water, less than half the medium concentration. Cell SO4 was increased to 3.0mm by adding SITS to the serosal side. Despite net transport rates greater than 1.4 μEq hr−1 cm−2, neither addition of SO4 to the SO4-free medium nor addition of SITS to SO4-containing medium altered short-circuit current. The results suggest that (1) ileal SO4 absorption consists of Na-coupled influx (symport) across the brush border and Cl-coupled efflux (antiport) across the basolateral membrane; (2) the overall process is electrically neutral; (3) the medium-to-cell Cl concentration difference may provide part of the driving force for net SO4 absorption; and (4) since agents affecting Cl fluxes (both absorptive and secretory) have little effect on SO4 fluxes, the mechanisms for their transcellular transports are under separate regulation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870981
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