Cytosolic Ca ²⁺ Elevation and Calpain Inhibitors in HgCl ₂ Injury to Rat Kidney Proximal Tubule Epithelial Cells

Abstract

This study assessed HgCl<sub>2</sub> injury to proximal tubule epithelial cells as it relates to the concentration of ionized cytosolic Ca2+ ([Ca2+]<sub>i</sub>) elevation and activation of calpains. Experiments in high and low extracellular Ca2+ concentration ([Ca2+]<sub>e</sub>) were performed using the calpain inhibitors antipain and leupeptin, and also trypsin inhibitor, methylamine, chloroquine, and ryanodine. Cell killing was time/dose dependent and greater with high [Ca2+]<sub>e</sub>. After 30 min treatment with 25 µMHgCl<sub>2</sub>, 19% of cells in low [Ca2+]<sub>e</sub> were dead while 72% died in high [Ca2+]<sub>e</sub>. Morphologic changes such as cytoplasmic blebbing were also greater in high [Ca2+]<sub>e</sub>. Antipain and leupeptin diminished toxicity. Leupeptin did not block Ca2+ entry into cells. Results show that HgCl<sub>2</sub> toxicity is correlated with increased [Ca2+]<sub>i</sub>, and that calpains may mediate the resultant pathological changes.