Effect of ionophore RO 2-2985 on the efflux of calcium from the rat nephron.

The effect of the ionophore RO 2-2985 on the efflux of calcium from the renal tubule was studied employing the in vivo microinjection technique. Microinjection solutions contained either RO 2-2985 (E) or its diluent (C). Following microinjections into the early proximal tubule, urinary 45Ca recoveries averaged 10.1 +/- 1.9 (C) and 3.5 +/- 1.4% (E) (P is less than 0.005), while recoveries averaged 32.3 +/- 6.9 (C) and 24.9 +/- 6.5% (E) (P is less than 0.05) following microinjections into the late proximal tubule. To determine if the decreased recovery of calcium was a specific effect, the effect of RO 2-2985 on the efflux of sodium, phosphate, and 3-O-methyl-D-glucose was examined. Compared to controls, RO2-2985 did not affect the urinary recoveries of 22Na, [32P]orthophosphoric acid, or 3-O-methyl-D-[14C]glucose. These studies demonstrate that RO 2-2985 enhances the efflux of calcium microinjected into the proximal portions of the rat nephron.