Mitochondria depletion abolishes agonist-induced Ca2+plateau in airway smooth muscle cells: potential role of H2O2

Abstract

The mechanisms by which mitochondria regulate the sustained phase of agonist-induced responses in cytosolic Ca(2+) concentration as an independent organelle in whole is not clear. By exposing to ethidium bromide and supplying pyruvate and uridine, we established mitochondrial DNA (mtDNA)-depleted rat airway smooth muscle cells (RASMCs) with maintained cellular energy. Upon an exposure to 2 microM histamine, [Ca(2+)](i) in control RASMCs increased to a peak followed by a plateau above baseline, whereas [Ca(2+)](i) in mtDNA-depleted RASMCs jumped to a peak and then declined to baseline without any plateau. mtDNA depletion apparently attenuated intracellular reactive oxygen species generation induced by histamine. By coexposure to 2 microM histamine and 0.1 microM exogenous H(2)O(2), which did not affect [Ca(2+)](i) by itself, the above difference in [Ca(2+)](i) kinetics in mtDNA-depleted RASMCs was reversed. Intracellular H(2)O(2) decomposition abolishes histamine-induced sustained elevation in [Ca(2+)](i) in RASMCs. Thus, mitochondria regulate agonist-induced sustained [Ca(2+)](i) elevation by a H(2)O(2)-dependent mechanism.