THE MEMBRANE MOLECULAR MECHANISM OF ACTIVE CHLORIDE TRANSPORT IN EPITHELIA (DIURETICS)

Date

1984

Authors

HANNAFIN, JO A.

Journal Title

Journal ISSN

Volume Title

Publisher

ProQuest Dissertations & Theses

YU Faculty Profile

Abstract

The elasmobranch rectal gland and mammalian thick ascending limb of Henle's loop (TALH) exhibit active chloride transport that is dependent on the presence of sodium and potassium and inhibited by "loop diuretics". The molecular mechanism of chloride transport was investigated using the rectal gland as a model as it shows transport characteristics similar to the TALH but is more readily available.;Plasma membrane vesicles were isolated from rectal gland and the sodium, rubidium (used as a substitute for potassium), and chloride fluxes were determined by a rapid filtration technique. The uptake of ('36)Cl was shown to be dependent on the presence of sodium and potassium and inhibited by bumetanide. ('22)Na uptake was shown to be dependent on the presence of potassium and chloride and inhibited by bumetanide. ('86)Rb uptake was inhibited by bumetanide and dependent on the presence of sodium and chloride. The interaction of the loop diuretics with the transport system was investigated in binding studies on rectal gland glasma membranes utilizing {lcub}('3)H{rcub} N-methylfurosemide and {lcub}('3)H{rcub} piretanide as probes. These studies revealed that the binding of the loop diuretics is dependent on the presence of sodium and potassium and inhibited by high concentrations of chloride.;These studies provide direct evidence for the existence of a N-K-Cl cotransport system in rectal gland plasma membrane vesicles. Loop diuretics appear to inhibit Na-K-Cl cotransport via competition with chloride for its binding site(s) on the cotransport system. Occupancy of the sodium and potassium transport sites of the cotransport system by the respective cations is necessary for the interaction of chloride or the loop diuretics with the cotransport system. This system is probably not unique to the elasmobranch rectal gland but also appears to be present in the mammalian TALH, where the uptake of ('36)Cl by plasma membrane vesicles was shown to be sodium and potassium dependent, and bumetanide sensitive. The uptake of ('22)Na by TALH plasma membrane vesicles was also shown to be potassium and chloride dependent and inhibited by bumetanide. Thus active chloride transport across these two epithelia involves coupling of sodium, potassium, and chloride fluxes via a cotransport system.

Description

Keywords

Animal Physiology.

Citation

Source: Dissertation Abstracts International, Volume: 44-11, Section: B, page: 3318.