Intrarenal distribution of exchangeable calcium in HgCl2-induced acute tubular necrosis

We used autoradiography to localize 45Ca accumulated in vitro by rat kidney that had been injured by HgCl2 in vivo. HgCl2, 1 mg/kg, was administered IV to male Sprague-Dawley rats and nephrectomies were performed from 15 min-30 days later. Kidney slices were incubated in KRB buffer containing 2 mM 45Ca at 25 degrees C for 180 min. The 45Ca slice-to-medium concentration ratio (S/M) increased significantly from a control mean of 0.8 +/- 0.04 SD (n = 4) to 1.6 +/- 0.3 (n = 4) after 1 day and reached 4.6 +/- 4.2 (n = 6) after 3 days. The serum creatinine increased more rapidly, from a control mean of 0.4 +/- 0.1 mg/dl to 0.7 +/- 0.1, 3.3 +/- 0.2, 7.2 +/- 1.6 after 4 hr, 1 day, and 3 days, respectively. Autoradiographic localization of 45Ca was first evident in necrotic proximal tubule (PT) straight segments after 1 day and was maximal at 3 days. 45Ca uptake was increased by slice incubation with N2 instead of O2, but anoxia did not alter the intrarenal distribution pattern. Necrotic PTs showing 45Ca by autoradiography were also positive by the von Kossa stain. Autoradiographs prepared from paraffin or Epon sections showed the same intrarenal distribution of 45Ca as section freeze-dry autoradiographs. Increased tissue 45Ca was due primarily to uptake by nephrocalcinotic PT segments; 40Ca accumulated in vivo exchanged for 45Ca during in vitro incubation. The exchangeable intrarenal calcium observed in this autoradiographic study was due to HgCl2-induced nephrocalcinosis.