Cl- channels in basolateral TAL membranes. XIX. Cytosolic Cl- regulates mmCIC-Ka and mcCIC-Ka channels

Induction of renal endonuclease G by cisplatin is reduced in DNase I-deficient mice

Nephrotoxicity from the chemotherapeutic drug cisplatin is associated with DNA fragmentation and cell death. We have recently demonstrated that DNase I knockout mice are significantly protected against cisplatin nephrotoxicity, but it is unknown whether the DNA fragmentation that occurs is produced by DNase I or another endonuclease. In this study we assessed the expression of several endonucleases involved in cell death after injection of cisplatin and found that the expression of endonuclease G (EndoG) increased whereas the expression of DNase I decreased almost to zero. Immunostaining showed that some nuclei contained both fragmented DNA and EndoG, suggesting that EndoG may cause DNA fragmentation induced by cisplatin. The increase in expression of EndoG was greater in wild-type mice than in DNase I knockout mice, indicating a potential link between the two endonucleases. In support of such a link, overexpression of DNase I in cultured mouse tubular epithelial cells also induced EndoG. Furthermore, gene silencing of EndoG in vitro provided significant protection against cell death. Taken together, our data suggest that both DNase I and EndoG mediate cisplatin injury to tubular epithelial cells.

Chloride channels in basolateral TAL membranes. XVIII. Phenylglyoxal induces functional mcCIC-Ka activity in basolateral MTAL membranes

Cultured mouse MTAL cells contain more mRNA encoding the Cl- channel mcCIC-Ka, which mediates CTAL Cl- absorption, than mRNA encoding the Cl- channel mmCIC-Ka, which mediates MTAL Cl- absorption. mmCIC-Ka and mcCIC-Ka have three functional differences: 1) mmCIC-Ka open time probability, Po, increases with increasing cytosolic Cl-, but variations in cytosolic Cl- do not affect Po in mcCIC-Ka; 2) mmCIC-Ka is gated by (ATP + PKA), while (ATP + PKA) have no effect on Po in mcCIC-Ka; and 3) mmCIC-Ka channels have single-ion occupancy, while mcCIC-Ka channels have multi-ion occupancy. Using basolateral vesicles from MTAL cells fused into bilayers, we evaluated the effects of 1 mM cytosolic phenylglyoxal (PGO), which binds covalently to lysine or arginine, on Cl- channels. With PGO pretreatment, Cl- channels were uniformly not gated either with increases in cytosolic-face Cl- or with (ATP + PKA) at 2 mM cytosolic-face Cl-; and they exhibited multi-ion occupancy kinetics typical for mcCIC-Ka channels. Thus, in basolateral MTAL membranes, blockade of Cl- access to arginine or lysine residues on mmCIC-Ka by PGO results in Cl- channels having the functional characteristics of mcCIC-Ka channels.