Signaling mechanisms of elevated neutrophil O2- generation afterburn injury

A full skin thickness burn injury was produced in anesthetized rats by exposing 25% of total body surface area to 98 degrees C water for 10 s. Sham (exposed to 37 degrees C water)and burn rats were killed 1, 3, 7, or 10 days later. The role of Ca2+ signaling and Ca2+-related protein kinase C (PKC) activation in neutrophil O-2(-) generation was ascertained by evaluating the effect of treatment of the rats with the Ca2+ entry blocker, diltiazem. There was an overt enhancement of O-2(-) generation by polymorphonuclear leukocytes from burn rats on days 1, 3, and 7 postburn, with the peak release occurring on day 3 postburn. O-2(-) generation comparable to the sham was noted on day 10 after the burn. O-2(-) releases on days 1, 3, and 7 postburn were accompanied by marked elevation of Ca-i(2+) and PKC responses. Like the O-2(-) release, intracellular Ca2+ concentration ([Ca2+](i)) response on day 10 after burn was suppressed to levels found in the sham group. The treatment of burn rats with diltiazem prevented the upregulation of both [Ca2+](i) and PKC responses as wells O-2(-) generation in neutrophils in rats on days 1, 3, and 7 after the burn. Because previous studies have shown that increases in [Ca2+](i) precede O-2(-) generation and degranulation, our results suggest that neutrophil O-2(-) release enhancement in the early stages after burn injury (e.g., days 1-7 postburn) results from an overactivation of the Ca-i(2+) and PKC signaling pathways. The heightened O-2(-) generation during the early burn injury phase might play a role in tissue damage in one or more of host organs.