Regulation of 109Cd2+ uptake into isolated neurohypophysial peptidergic nerve terminals.
Cadmium (109Cd2+) uptake was studied in a preparation of isolated neurohypophysial nerve terminals. By use of a filter separation method, together with a permeabilizing agent (Triton X-100), two cellular Cd2+ pools have been distinguished. The uptake into the intraterminal pool was governed mainly by a process that displayed saturable kinetics, with a Vmax of 0.15 nmol of Cd2+/mg of protein/min and a Km of 0.18 mM, consistent with a transport system. The superficially bound Cd2+ pool (Triton insensitive), which represented 30-50% of the total Cd2+ bound to the cellular system, was very sensitive to the ionic composition of the incubation medium. Reducing the extracellular Ca2+ or Na+ concentration caused a significant increase in the size of the Triton-insensitive Cd2+ pool. Whereas Na+ did not affect Cd2+ uptake, Ca2+ induced a small, but significant, increase of Cd2+ uptake into the terminals. It is concluded that there is a significant intraterminal uptake of Cd2+, which could explain several physiological effects of this ion.
Department of Human Anatomy, Oxford University, England.
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Toescu
D000818:Animals; D002104:Cadmium / Q000493:pharmacokinetics*; D002106:Cadmium Radioisotopes; D002118:Calcium / Q000378:metabolism; D003470:Culture Media; D005110:Extracellular Space / Q000378:metabolism; D007477:Ions; D008297:Male; D009411:Nerve Endings / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism
D002106:Cadmium Radioisotopes; D003470:Culture Media; D007477:Ions; D010455:Peptides; D002104:Cadmium; D012964:Sodium; D002118:Calcium