Oxidative stress-induced calcium signalling in Aspergillus nidulans

The effect; of oxidative stress on levels of calcium ion (Ca2+) in Aspergillus nidulans were measured using strains expressing aequorin in the cytoplasm (Aeq(cyt)) and mitochondria (Aeq(mt)). When oxidative stress was induced by exposure to 10-mM H2O2 the mitochondrial calcium response (C a,;) was greater than the change in cytoplasmic calcium (Ca-c(2+)). The Ca-mt(2+) response to H2O2 was dose dependent, while the increase in [Ca-c(2+)] did not change with increasing H2O2. The increase in both [Ca-c(2+)] and [Ca-mt(2+)] in response to oxidative stress was enhanced by exposure of cells to Ca2+. The presence of chelator in the external medium only partially inhibited the Ca-mt(2+) and Ca-c(2+) responses to oxidative stress. Reagents that alter calcium fluxes had varied effects on the Cap response to peroxide. Ruthenium red blocked the increase in [Ca-mt(2+)], while neomycin caused an even greater increase in [Ca-mt(2+)]. Treatment with ruthenium red and neomycin had no effect on the Ca-c(2+) response. Bafilomycin A and oligomycin had no effect on either the mitochondrial or cytoplasmic response. Inhibitors of both voltage-regulated calcium channels and intracellular calcium release channels inhibited the Ca2+-dependent component of the Ca-mt(2+) response to oxidative stress. We conclude that the more significant Ca2+ response to oxidatve stress occurs in the mitochondria and that both intracellular and extracellular calcium pools can contribute to the increases in [Ca-c(2+)] and [Ca-mt(2+)] induced by oxidative stress. (C) 2002 Elsevier Science Inc. All rights reserved.