Cyclosporin increases the density of angiotensin II subtype 1 (AT1) receptors in XXXX medullary thick ascending limb cells.

@entity19 @entity15395 @entity26549 @entity1129
BACKGROUND: Cyclosporin A (CsA), a potent immunosuppressive agent, can be nephrotoxic. Because clinical studies have suggested that the intrarenal renin-angiotensin system may be involved in the mechanism responsible for CsA nephrotoxicity, we have analysed the effects of CsA on angiotensin II ( @entity15395 ) receptors in medullary thick ascending limb (mTAL) cells known to be sensitive to the action of CsA. METHODS: Experiments were carried out on subcultured @entity19 mTAL cells. The expression of mRNA of @entity15395 subtype 1 and 2 ( @entity1129 (1) and @entity1129 (2)) receptors was investigated using reverse transcription-polymerase chain reaction (RT-PCR). [(3)H] @entity15395 was used for radioligand and binding studies. Fluorimetric recordings using the fluorescent dye fura-2/AM were performed to determine the effect of CsA on the intracellular calcium ([Ca(2+)]i) content of untreated and @entity26549 II-treated mTAL cells. RESULTS: Subcultured mTAL cells expressed @entity1129 (1) and @entity1129 (2) @entity15395 receptor mRNAs, and binding studies revealed that the @entity1129 (1) receptors were the predominant @entity15395 receptor subtype ( approximately 90%) in mTAL cells. CsA (100 ng/ml, 24 h) increased (1.7-fold) the number of @entity15395 receptors (untreated, 315.8; +CsA, 543.6 fmol/mg protein) without altering the K(D) (untreated, 7.16; +CsA, 7.06 nM). CsA also significantly increased the level of [Ca(2+)]i measured in cultured mTAL cells both in the basal state (-CSA, 72.2; +CsA, 93.4 nM/10(6) cells) and in the presence of @entity15395 (-CSA, 97.8; +CsA, 206.3 nM/10(6) cells). CONCLUSIONS: These findings suggest that the increase in @entity15395 @entity1129 (1) receptors and [Ca(2+)]i caused by CsA may be involved in the mechanism(s) responsible for CsA nephrotoxicity.
