Acute calcium nephrotoxicity. An electron microscopical and semiquantitative light microscopical study.

Rats were infused for three hours with doses of calcium gluconate to elevate serum calcium level and were killed either immediately after infusion or after 24 hours. Necrosis of proximal tubular cells was observed when serum calcium level was 16.0 mg/dl or higher. Above 16.0 mg/dl, an additional 5% of renal tubular profiles contained damaged cells for each 1 mg/dl in serum calcium. No difference in extent of damage was found in rats killed immediately or after 24 hours. Initial changes were formation of granular dense bodies in mitochondria, cell swelling, rupture, and extensive mitochondrial calcification. Renal tubular basement membrane changes appeared to be initiated by protrusion of cytoplasmic buds, forming ovoid bodies, which became embedded in the basement membrane. These ovoid bodies then appeared to serve as a nidus for further extensive basement membrane calcification.