In the kidney, cell injury resulting from
ischemia and
hypoxia is thought to be due, in part, to increased cytosolic Ca(2+) levels, [Ca(2+)]i, leading to activation of lytic
enzymes, cell dysfunction, and
necrosis. We report evidence of a progressive and exponential increase in [Ca(2+)]i (from 245 +/- 10 to 975 +/- 100 nM at 45 mins), cell permeabilization and
propidium iodide (PI) staining of the nucleus, and partial loss of cell transport functions such as Na(+)-gradient-dependent uptakes of (14)C-alpha-methylglucopyranoside and
inorganic phosphate ((32)Pi) in proximal convoluted tubules of adult rabbits subjected to
hypoxia. The rise in [Ca(2+)]i depended on the presence of extracellular [Ca(2+)] and could be blocked by 50 microM Ni(2+)but not by
verapamil (100 microM). Presence of 50 microM Ni(2+) also reduced the
hypoxia-induced morphological and functional
injuries. We also used HEK 293 cells, a kidney cell line, incubated in media without
glucose and exposed for 3.5 hrs to 1% O(2)-5% CO(2) and then returned to
glucose-containing media for another 3.5 hrs in an air-5% CO(2) atmosphere and finally exposed for 1 min to media containing 1 microM PI. NiCl(2) (50 microM) or
pentobarbital (300 microM) more than
phenobarbital (1.5 mM), when present in the incubation medium during both the hypoxic and the reoxygenation periods, induced significant (P < 0.001) reductions in the number of cell nuclei stained with PI, similar to their relative potency as inhibitors of T channels. Our findings indicate that
hypoxia-induced alterations in
calcium level and subsequent cell injury in the proximal convoluted tubule and in HEK cells involve a
nickel-sensitive and
dihydropyridine insensitive pathway or channel.