In vitro effects of cyclosporine and FK 506 on the renal cortex.

C YCLOSPORINE (CyA) and FK 506 are the effective immunosuppressive agents used in human organ transplantation and a variety of autoimmune diseases. 1-3 The nephrotoxicity of Cy A is well known. 4 • 5 Preliminary reports indicate the nephrotoxic nature of FK 506. though the clinical significance is yet to be established. especially in view of the favorable side effect profile that FK 506 possesses.6-8 The mechanism of nephrotoxicity of Cy A is not clearly established. Direct toxicity on the cell and cell membranes. altered prostaglandin synthesis. changes in the handling of calcium by the cells. and hemodynamic alterations have all been implicated. 9 Very little is known about the toxicity of FK 506. There is paucity of data on the direct effects of Cy A and FK 506 on renal tissue. Here we report the in vitro effects of both CyA and FK 506 on the calcium sequestration by the microsomes and mito-chondria of renal cortical tissue. Adult male. white New Zealand rabbits were killed. The kidneys were perfused in situ with HEPES (10 mmollL) and sucrose (0.25 mol/L) medium (pH 7.35). The kidneys were removed and the cortices were dissected and homogeruzed in the same medium (10 mUg). Mitochondria and microsome were isolated by high speed and ultracentrifugation as described. lo and stored under liquid nitrogen until they were used for the studies. The protein concentration was measured with the Biorad reo agent. II The ATPase activity was calculated from the amount of the inorganic phosphate released in the presence of the mi-crosomes (50 ILg protein), ATP (3 mmollLl. and EGTA (I mmollLl with or without calcium chloride (2 mmoIlL). Inorganic phosphate was measured according to the method of Fiske and Subba ROW.12 with 10% ascorbic acid as the reducing agent. Calcium m the suspending medium was measured with the metailochrome indicator Anenazo Ill.') The calcium concentration was continuously followed at a wavelength pair of 665 nm and 685 nm in the dual-wavelength spectrophotometer (Biomedical instrumentation, Univenity of Pennsylvania. Johnson Research Foundation. Philadelphia. Penn). The effect of I to 10 !J.8/mL of either C y A or FK 506 on calcium sequestration was compared to the control values obtained in the presence of DMSO (10 ",L). The microsomal preparation was unaffected by 1 mmollL NaN). The mitochondrial calcium uptake was completely blocked by both NaN, (1 mmollLl and FCCP (S /LffioIlL) , thus confirming the nature of the …