Primary effects of metals on osmoregulatory processes
- MUSC, Charleston, SC (United States)
- Gulbenkian Inst. of Science, Oeiras (Portugal)
- Univ. of Wyoming, Laramie, WY (United States)
Isolated skins of the bullfrog, Rana catesbiana, were chamber-mounted as sheets, bathed on the inside (serosa) with a Ringer`s solution but on the outside with simulations of freshwater to mimic environmental conditions. An automatic voltage-clamping protocol measured short-circuit current (I{sub sc}), an index of transepithelial Na{sup +} transport, and total tissue conductance (G{sub t}). Aluminum, cadmium, chromium, copper, lead, mercury and zinc were studied separately as additives to the outer bath and yielded qualitatively similar results. Al has been most thoroughly examined. At 200 ppB (7.4 {micro}M) or more, and at pH 5.0 or below, Al inhibits both I{sub sc} and G{sub t}. Effects are precluded by the addition of amiloride, a diuretic that blocks Na{sup +} transport at the level of the Na{sup +} channel. Kinetic analysis reveals that Al and amiloride compete for a single binding site on the channel protein. At levels of 10 ppM, Al addition results in amiloride-insensitive increases in G{sub t} (10-fold or more) and I{sub sc} (20+ {micro}A/cm{sup 2}). Isotopic flux measurements suggest that these effects are due to an ``opening`` of epithelial tight junctions with passive, downhill diffusion of salt from inside to outside; the polarity of the resulting current reflects enhanced paracellular permeability with specificity for Cl{sup {minus}} over Na{sup +}. Varying medium pH indicates that Al{sup 3+} is the dominant species in each of the two effects. Al addition to the inner bathing medium was without effect despite access to the Na{sup +}-K{sup +}-ATPase. Contaminant metals may interfere with osmoregulation by impairing salt accumulation and by enlarging leak pathways through which solutes are lost to the environment.
- OSTI ID:
- 392351
- Report Number(s):
- CONF-9511137-; ISBN 1-880611-03-1; TRN: IM9647%%205
- Resource Relation:
- Conference: 2. Society of Environmental Toxicology and Chemistry (SETAC) world conference, Vancouver (Canada), 5-9 Nov 1995; Other Information: PBD: 1995; Related Information: Is Part Of Second SETAC world congress (16. annual meeting): Abstract book. Global environmental protection: Science, politics, and common sense; PB: 378 p.
- Country of Publication:
- United States
- Language:
- English
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