Background:The TRPV6 amino acid sequence is predicted from its cDNA. Results: The TRPV6 protein purified from human tissues has an extended N terminus not present in the predicted protein. Conclusion:Full-length TRPV6 is trafficked to the plasma membrane, and its translation efficiency tightly controls TRPV6-mediated Ca 2ϩ entry. Significance: This study provides mechanistic insights into the function of the full-length TRPV6.

Incubation of lysate from human polymorphonucleated neutrophils and human platelets with r3'P]NAD resulted in the labeling of a 42-kDa protein. Phosphodiesterase (Crotalus durissus) released 5'-AMP from the radiolabeled protein. The 42-kDa protein was identified as actin by binding to DNAse-I, two-dimensional gel electrophoresis and partial proteolysis. The rate of ADP-ribosylation was greater with [32P]ADP-ribose than with [32P]NAD, indicating a non-enzymic modification. ADP-ribose also modified actin in the actin-DNAse-I complex, but denatured actin was not modified by ADP-ribose. Only cytoplasmic Ply-actin isoforms were non-enzymically ADP-ribosylated but not muscle a-actin. The acceptor amino acid was identified as a cysteine residue whereas the bacterial ADP-ribosyltransferase C. perfringens iota toxin catalyzes incorporation of ADP-ribose to Arg177 of actin. Alkylation of cysteine residues of actin with N-ethylmaleimide prevented subsequent non-enzymic ADP-ribosylation but not the toxin catalyzed modification. Non-enzymically ADP-ribosylated actin was further modified by C. pe$ringens iota toxin. The F-actin stabilizing mycotoxin phalloidin blocked the non-enzymic ADP-ribosylation and, conversely, ADP-ribosylation inhibited the phalloidin-induced polymerization of ADP-ribosylated actin. The data indicate that cytoplasmic actin is non-enzymically ADP-ribosylated by ADP-ribose at a cysteine residue to inhibit actin polymerization.Actin is one of the most abundant proteins in eukaryotic cells. Besides its important role in the organization of cell architecture (for review, see [l]), actin is involved in various cellular motile functions such as locomotion, cytoplasmic streaming, endocytosis and exocytosis 12-51. Actin is the substrate for several ADP-ribosylating bacterial toxins 16-81. The family of actin-modifying toxins comprises Clostridium botulinum C2 toxin [9], Clostridium perjringens iota toxin [lo, 111, Clostridium spiroforme toxin 112, 131 and an ADP-ribosyltransferase produced by Clostridium difficile 1141 (for review, see [8, 151). Using protein chemistry [16, 171 and site-directed mutagenesis 1181, it has been demonstrated that these toxins mono-ADP-ribosylate actin at Arg177. The toxin-catalyzed ADP-ribosylation grossly alters the biochemical and physiological functions of actin: Firstly, ADP-ribosylation inhibits the ability of actin to polymerize [ 10, 191. Secondly, ADP-ribosylated actin interacts with the fast growing, barbed ends of actin filaments in a manner similar to that of a capping protein and inhibits the polymerization of non-modified actin 120, 211. Thirdly, ADP-ribosylation inhibits monomeric G-actin ATPase activity [22, 231. Furthermore, recent studies indicate that the toxins ADP-ribosylate actin complexed with gelsolin, thereby altering the nucleation activity of the gelsolin-actin complex [24]. In intact cells, the pathophysiological effects of the toxin-cataCorrespondence to I. Just, lnstitut fur Pharmakologie und Toxikologie der Universitat des Saarlandes, D-66421 Homburg-S...

1. In rats iron was absorbed after administration into the gut lumen as ferric iron bound to serum albumin, to nitrilotriacetic acid, and to 8-OH-quinoline sulfonic acid, or as isolated diferri-transferrin. 2. Iron absorption from 59Fe-labelled transferrin was inhibited by the addition of rat plasma. 3. The inhibitory component in the rat plasma turned out to be ceruloplasmin (ferrous iron oxidase, EC 1.16.2.1). 4. The absorption of iron from these ferric iron complexes was also inhibited by addition to the incubation medium of ferrozine, a strong anionic Fe(II)-ligand. 5. Uptake and absorptive utilization of transferrin-bound ferric iron was decreased after a prewash of the gut lumen and could be restored by the addition of ascorbate to the incubation medium. 6. The conclusion was drawn from these results that luminal reduction precedes ferric iron absorption and that this is a prerequisite for the uptake into the mucosa.

SUMMARY1. Vasopressin enhanced the absorption of Na+ and C1-across the short-circuited colon descendens from normal rats. This effect of vasopressin results from an increase in the mucosal to serosal movement of Na+ and Cl-and a decrease in the serosal to mucosal movement of Cl-and was accompanied with a decrease in the short-circuit current (Ic). Neither the base-line absorption of Na+ and Cl-, the vasopressin-induced increase in Na+ and Cl-absorption nor the decrease in ISc were inhibited by amiloride in the colon from normal rats.2. Colon descendens from rats treated for 3 days with dexamethasone had remarkably higher transmural potential difference (p.d.), tissue conductance (Gt) and ISC. The absorption of Na+ across the short-circuited colon descendens from dexamethasone-treated rats was increased 3-fold when compared to colon from normal rats. The absorption of Cl-in normal rats was reversed to Cl-secretion in treated rats.3. Amiloride rapidly and reversibly decreased the p.d., Gt and I., in colon from dexamethasone-treated rats. The transport of Na+ was nearly completely inhibited by amiloride in treated rats. 4. In contrast to its enhancing effects on Na+ absorption in colon from normal rats vasopressin did not enhance Na+ absorption in colon from dexamethasone-treated rats. The enhancement of Cl-absorption by vasopressin was retained in colon from treated rats. This enhancement of Cl-transport was due solely to a decrease in the serosal to mucosal movement of Cl-and was accompanied with a decrease in Isc and at.5. The results support the hypothesis that vasopressin causes inhibition of the electrogenic secretion of Cl-in colon from dexamethasone-treated rats. Furthermore, the results suggest that the increase in the mucosal to serosal movement of Na+ and Cl-and the decrease in the serosal to mucosal movement of Cl-in colon from normal rats are caused by independent effects of vasopressin.

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