Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus

Journal Article · Sun May 01 00:00:00 EDT 1983 · J. Gen. Physiol.; (United States)

DOI:https://doi.org/10.1085/jgp.81.5.643· OSTI ID:6723557

Chase, Jr, H S; Al-Awqati, Q

Regulation of the sodium permeability of the luminal membrane is the major mechanism by which the net rate of sodium transport across tight epithelia is varied. Previous evidence has suggested that the permeability of the luminal membrane might be regulated by changes in intracellular sodium or calcium activities. To test this directly, we isolated a fraction of the plasma membrane from the toad urinary bladder, which contains a fast, amiloride-sensitive sodium flux with characteristics similar to those of the native luminal membrane. Using a flow-quench apparatus to measure the initial rate of sodium efflux from these vesicles in the millisecond time range, we have demonstrated that the isotope exchange permeability of these vesicles is very sensitive to calcium. Calcium reduces the sodium permeability, and the half-maximal inhibitory concentration is 0.5 microM, well within the range of calcium activity found in cells. Also, the permeability of the luminal membrane vesicles is little affected by the ambient sodium concentration. These results, when taken together with studies on whole tissue, suggest that cell calcium may be an important regulator of transepithelial sodium transport by its effect on luminal sodium permeability. The effect of cell sodium on permeability may be mediated by calcium rather than by sodium itself.

• Research Organization: Columbia Univ., New York, NY (United States)
• OSTI ID: 6723557
• Journal Information: J. Gen. Physiol.; (United States), Vol. 81:5
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
CALCIUM COMPOUNDS
BIOLOGICAL EFFECTS
CELL MEMBRANES
PERMEABILITY
SODIUM COMPOUNDS
MEMBRANE TRANSPORT
SODIUM ISOTOPES
TRACER TECHNIQUES
BLADDER
TOADS
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BODY
CELL CONSTITUENTS
ISOTOPE APPLICATIONS
ISOTOPES
MEMBRANES
ORGANS
URINARY TRACT
VERTEBRATES
551001* - Physiological Systems- Tracer Techniques