Integumentary L-histidine transport in a euryhaline polychaete worm: regulatory roles of calcium and cadmium in the transport event.
Integumentary uptake of L-[(3)H]histidine by polychaete worms (Nereis succinea) from estuarine waters of Oahu, Hawaii was measured in the presence and absence of calcium and cadmium using a physiological saline that approximated the ion composition of 60 % sea water. In this medium 1 micromol L(-1) cadmium significantly increased (P<0.01) the uptake of 10 micromol L(-1)L-[(3)H]histidine, while 1 micromol L(-1) cadmium plus 25 micromol L(-1)L-leucine significantly decreased (P<0.01) amino acid uptake. L-[(3)H]histidine influx was a sigmoidal function (n=2. 21+/-0.16, mean +/- s.e.m.) of [L-histidine] (1?50 micromol L(-1)) in the absence of cadmium, but became a hyperbolic function with the addition of 1 micromol L(-1) cadmium. A decrease of calcium concentration from 6 to 0 mmol L(-1) (lithium substitution) significantly increased (P<0.01) amino acid influx in the presence and absence of cadmium. Calcium significantly reduced (P<0.01), and cadmium significantly increased (P<0.01), L-[(3)H]histidine influx J(max), without either divalent cation affecting amino acid influx K(t). Variation in external sodium concentration (0?250 mmol L(-1)) had no effect on 10 micromol L(-1)L-[(3)H]histidine influx, but amino acid entry was a sigmoidal function of both [cadmium] (n=2.34+/-0.44) and [lithium] (n=1.91+/-0.39) in the absence of calcium. A model is proposed for transapical L-[(3)H]histidine influx by a transporter that resembles the classical sodium-independent L-system carrier protein that is regulated by the external divalent cations calcium and cadmium.
Ahearn
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HR
Department of Zoology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA. ahearn@hawaii.edu
Ahearn
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Gomme
J
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D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D006639:Histidine / Q000378:metabolism*; D007700:Kinetics; D007930:Leucine / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D008954:Models, Biological; D011077:Polychaeta / Q000378:metabolism*
D002104:Cadmium; D006639:Histidine; D008094:Lithium; D007930:Leucine; D002118:Calcium