Cyclosporine stimulates Na+-K+-Cl- cotransport activity in cultured mouse medullary thick ascending limb cells.
BACKGROUND
Cyclosporine (CsA) has been shown to alter the activity of plasma membrane transporters in kidney epithelial cells. In this study, we have investigated the effects of CsA on Na+,K+-ATPase and Na+-K+-Cl- cotransport activities in cultured cells derived from microdissected mouse medullary thick ascending limb (mTAL) cells.


METHODS
Experiments were carried out on subcultured confluent mouse TAL cells. Reverse transcription-polymerase chain reaction experiments showed that they expressed the mNKCC2 electroneutral Na+-K+-Cl- cotransporter and ROM-K1 and ROMK2 potassium channel mRNA. Western blotting also revealed the presence of the 40 kD ROMK protein using an anti-ROMK antibody. The effect of CsA (100 ng/mL) on ion transport was assessed by measuring the influx and efflux of rubidium (86Rb+) and 36Cl-, used as tracers of K+ and Cl- movements, on cells grown on Petri dishes or permeable filters.


RESULTS
CsA inhibited by 38% the ouabain-sensitive component of 86Rb+ influx mediated by the Na+,K+-ATPase pumps. CsA also increased by 38% the ouabain-resistant furosemide-sensitive component (Or-Fs) of 86Rb+ influx, reflecting the Na+-K+-Cl- cotransport activity and stimulated the basolateral efflux of 36Cl- from mTAL cells grown on filters. The CsA-stimulated basal efflux of Cl- was prevented by the basal addition of the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB, 10-4 mol/L). Apical addition of the K+ channel blocking agent Ba2+ (10-4 mol/L) partially prevented the CsA-stimulated basal efflux of Cl-. Adding Ba2+ to the luminal side of cells grown on Petri dishes also prevented the rise in apical 86Rb+ efflux and the increased Or-Fs component of 86Rb+ influx caused by CsA.


CONCLUSIONS
These results indicated that CsA may stimulate the Na+-K+-Cl- cotransport activity and also suggested that this immunosuppressive agent may interfere in the recycling of apical K+ in this model of cultured mouse TAL cells.
Wu
M S
MS
Division of Nephrology, Chang Gung Memorial Hospital, Taipei, Taiwan. maisuwu@ms9.hinet.net
Yang
C W
CW
Bens
M
M
Peng
K C
KC
Yu
H M
HM
Vandewalle
A
A
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology*; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006084:Graft Rejection / Q000188:drug therapy / Q000378:metabolism; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D016030:Kidney Transplantation / Q000502:physiology; D008138:Loop of Henle / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D012414:Rubidium Radioisotopes / Q000493:pharmacokinetics; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D002352:Carrier Proteins; D002712:Chlorides; D007166:Immunosuppressive Agents; C510693:Kcnj1 protein, mouse; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012414:Rubidium Radioisotopes; D028021:Sodium-Potassium-Chloride Symporters; D001464:Barium; D016572:Cyclosporine; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium