Lack of Changes in Cytosolic Ionized Calcium in Primary Cultures of Rat Kidney Cortical Cells Exposed to Cytotoxic Concentrations of Gentamicin: A Fluorescent Digital Imaging Method for Assessing Changes in Cytosolic Ionized Calcium

A digitized fluorescence imaging study of intracellular free calcium, mitochondrial integrity and cytotoxicity in rat renal cells exposed to ionomycin, a calcium ionophore

The objective of this study was to explore the role of extracellular Ca2+ and mitochondrial integrity in ionomycin-induced cytotoxicity in primary cultures of rat kidney cortical epithelial cells using digitized fluorescence imaging (DFI), which is a powerful tool for continuously observing the dynamic intracellular biochemistry of single living cells. Using DFI, intracellular free calcium ion concentration ([Ca2+]i), mitochondrial membrane potential and loss of cell viability in individual rat renal cortical epithelial cells were examined temporally by fura-2, rhodamine 123 (Rh-123) and propidium iodide (PI), respectively. Images were taken within 10 min after exposure to 5 and 10 microM ionomycin. These three parameters, [Ca2+]i, mitochondrial membrane potential and cell viability, were also measured in populations of cells by a multiwell fluorescence scanner with fluo-3, Rh-123 and PI, respectively. Cytotoxicity was also assessed by two colorimetric cytotoxicity tests (LDH leakage and mitochondrial MTT reduction). Using DFI, the fluorescence scanner and the colorimetric cytotoxicity tests, we found that exposure of primary cultures of rat kidney cortical epithelial cells to high concentrations of ionomycin (5 and 10 microM) caused a rapid and sustained rise in [Ca2+]i, which preceded dissipation of the mitochondrial membrane potential and loss of cell viability and that chelation of extracellular Ca2+ with EGTA attenuated these responses. We demonstrated the value of using DFI to continuously observe the dynamic intracellular biochemistry of single living cells by establishing a sequence of elevated [Ca2+]i, dissipation of mitochondrial membrane potential and cytotoxicity. We conclude that a combination of the influx of extracellular Ca2+ and loss of mitochondrial integrity may be responsible for the cytotoxicity observed in individual renal cells and populations of renal cells after treatment with ionomycin.

Gentamicin nephrotoxicity in rats is not modified by verapamil

To assess whether calcium could be involved in the gentamicin-induced nephrotoxicity, we have studied the effect of the calcium channel blocker verapamil on renal function in rats intoxicated by gentamicin. Male Wistar rats were divided in three groups. In group I (n = 7) they were injected with gentamicin 100 mg/kg body wt/day s.c. for 5 days. In group II (n = 6), they received gentamicin and verapamil s.c. 2 mg/rat/day. In group III rats served as control. Plasma creatinine and creatinine clearance were daily measured. Rats treated with gentamicin showed a progressive increase in plasma creatinine and a drop in creatinine clearance. No differences between rats treated with gentamicin and those with gentamicin plus verapamil were observed. The urinary flow decreased after treatment with gentamicin, this decrease being more marked in rats treated with verapamil. No differences in daily urinary sodium and potassium excretion were found between intoxicated rats treated or not with verapamil. The present results show that, in rats, verapamil has no protective effect against the nephrotoxicity of gentamicin.