PT  - JOURNAL ARTICLE
AU  - Tsuruoka, Shuichi
AU  - Sugimoto, Koh-ichi
AU  - Muto, Shigeaki
AU  - Nomiyama, Kazuo
AU  - Fujimura, Akio
AU  - Imai, Masashi
TI  - Acute Effect of Cadmium-Metallothionein on Glucose and Amino Acid Transport across the Apical Membrane of the Rabbit Proximal Tubule Perfused In Vitro
DP  - 2000 Feb 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 769--777
VI  - 292
IP  - 2
4099  - http://jpet.aspetjournals.org/content/292/2/769.short
4100  - http://jpet.aspetjournals.org/content/292/2/769.full
SO  - J Pharmacol Exp Ther2000 Feb 01; 292
AB  - Acute as well as chronic exposure of cadmium (Cd) leads to proximal tubule injury. The exact cellular mechanism of this disorder and whether there is a contribution of cadmium-metallothionein (Cd-MT), a binding protein of Cd, remain unclear. We perfused isolated S2 segments of rabbit nephron, and the deflections of transmural voltage (ΔVt) and apical membrane voltage (ΔVa) on elimination of glucose or alanine from the perfusate were measured for the parameters of activity of Na+-glucose and Na+-amino acid cotransporters. The effects of Cd-MT or CdCl2 to either bath or lumen for 10 min on these parameters were examined. We also measured the lumen-to-bath [14C]glucose flux. Addition of Cd-MT to lumen suppressed glucose- or alanine-dependent ΔVt and ΔVa, as well as baseline Vt and basolateral membrane voltage (Vb), at approximately 10 min. [14C]glucose flux was inhibited by Cd-MT to lumen. The effects of Cd-MT to bath and CdCl2 to either lumen or bath were 100-fold less potent than that of Cd-MT to lumen. Luminal Cd-MT immediately suppressed the glucose-dependent ΔVa, whereas the baselineVa and Vt were unchanged. The early effect of luminal Cd-MT was simulated by addition of 10−4 M phloretin. Addition of 10−4 M ouabain to the bath simulated the later effect of Cd-MT. The protection of SH group by dithiothreitol prevented the early effect of Cd-MT, but not the later effect. We concluded that Cd-MT initially acts directly on Na+-glucose and Na+-amino acid cotransporters from the lumen by attacking SH group, followed by the later inhibition of Na+-K+-ATPase after entering the cell from the apical membrane. The American Society for Pharmacology and Experimental Therapeutics