Veron D, Martin RS, Escobar E, Tufaro D, Visconti P, Tezon JG, Arrizurieta EE. Effect of NPPB on chloride (Cl-) transport in distal colon of potassium (K+) adapted rats.
ACTA PHYSIOLOGICA SCANDINAVICA 1994;
151:45-50. [PMID:
8048335 DOI:
10.1111/j.1748-1716.1994.tb09719.x]
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Abstract
Secondary hyperaldosteronism enhances the rate of K secretion in distal colon, at least in part, through the stimulation of Na(+)-K(+)-Cl- cotransport across the basolateral membrane. To maintain a constant intracellular Cl- activity an increase in Cl- transport out of the cell must be assumed. We explored, under amiloride 10(-4) M and short circuited conditions, conductive pathways for Cl- exit in the distal colon of K(+)-adapted rats by means of a putative Cl- channel blocker, NPPB (5-nitro-2(3-phenyl-propylamino-benzoate. Results prior to NPPB showed an increase in JClms after K+ loading from 5.84 +/- 0.66 to 8.33 +/- 0.86 and JClsm from 4.77 +/- 0.55 to 8.16 +/- 0.96 microEq h-1 cm-2 (P < 0.001), when compared with controls. Net fluxes were not different between groups. Luminal NPPB in K+ adaptation resulted in a decrease of JClsm, from 7.85 +/- 1.5 to 6.69 +/- 1.5 microEq h-1 cm-2 (P < 0.05). There were no changes in both unidirectional Cl- fluxes in controls under luminal NPPB and in potential difference (V) and short-circuit current (Isc) under any condition. Finally, K+ adaptation resulted in an increase of luminal cyclic AMP (cAMP) concentration (0.09 +/- 0.02 to 0.20 +/- 0.03 pmol 100 microliters -1, P < 0.005), when compared with control rats. The data may suggest a transcellular recycling of Cl- and an activated NPPB inhibitable serosal to mucosal Cl- pathway on luminal membrane in the K+ adapted state, possibly mediated by an increase in cAMP production.
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