[Calcium dependence of the stimulating action of cadmium on organic acid transport in the frog kidney].
The stimulatory effect of cadmium ions on the Na-dependent fluorescein transport into the frog renal proximal tubules ceased with decreasing Ca++ concentration in solution on both the sides of the cell layer down to micromolar level. The decrease in Ca++ concentration per se stimulated fluorescein uptake during short-term incubations. A further diminution of Ca++ concentration in the tubular lumen with the aid of EGTA resulted in a sharp inhibition of the organic acid transport. Amiloride, which prevented the stimulatory effect of cadmium, inhibited the fluorescein transport at both millimolar and micromolar levels of Ca++ concentration, but it failed to affect the transport process after introducing EGTA into the tubular lumen. The results are discussed within the frames of a model regarding extracellular Ca++ as an allosteric inhibitor, and intracellular Ca++ as an allosteric activator of sodium channels in the apical membrane. Cd++ is assumed to compete with Ca++ for binding to centers of the allosteric inhibition, thereby accelerating the sodium ion flux across the cells of the proximal tubules.
D000085:Acetates / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology*; D019256:Cadmium Chloride; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D005452:Fluoresceins / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism; D008297:Male; D011896:Rana temporaria; D013268:Stimulation, Chemical
D000085:Acetates; D005452:Fluoresceins; D002104:Cadmium; D004533:Egtazic Acid; D019256:Cadmium Chloride; D002118:Calcium
Zavisimost' ot kal'tsiia stimuliruiushchego deĭstviia kadmiia na transport organicheskoĭ kisloty v pochke liagushki.