Role of [Ca2+]i in lethal oxidative injury in rat cultured inner medullary collecting duct cells

Reactive oxygen metabolites have been implicated in the pathogenesis of toxic, ischaemic and immunologically mediated renal injury. An increase in the cytosolic free Ca²⁺ concentration ([Ca²⁺]_i) has been proposed as a mechanism of oxidative stress-induced cell injury. We used a fluorescence spectrometer and a fluorescence probe to measure the [Ca²⁺]_i and viability of rat primary cultured inner medullary collecting duct (IMCD) cells during oxidative stress induced by 5 mM tert-butyl hydroperoxide (TBHP). Initially, this oxidative stress evoked a small increase in [Ca²⁺]_i which was followed by a slower sustained increase from the resting level of 170.8±38.8 nM to 1490.5±301.7 nM after 60 min, and this preceded the loss of plasma membrane integrity, measured by the propidium iodide fluorescence method. The elimination of extracellular Ca²⁺ from the culture medium prevented the TBHP-induced [Ca²⁺]_i increase and improved cell viability. Restoration of extracellular Ca²⁺ resulted in an immediate and large increase in [Ca²⁺]_i and extensive cell death. Verapamil, a Ca²⁺ channel blocker, inhibited the [Ca⁺]_i increase and afforded significant protection against cellular injury following exposure to TBHPinduced oxidative stress. Extracellular acidosis also prevented the increase in [Ca²⁺]_i and cell death caused by this oxidative stress. These results are consistent with the hypothesis that oxidative stress-induced IMCD cellular injury may be the result of increased [Ca²⁺]_i caused, in part, by activation of voltage-dependent Ca²⁺ channels.