Submitted on June 11, 2008
Revised on November 20, 2008
Accepted on December 16, 2008
Cellular Localization of Mitochondria Contributes to Kv Channel Mediated Regulation of Cellular Excitability in the Pulmonary, but not Mesenteric Circulation
Amy L. Firth1, Dmitri V Gordienko2, Kathryn H Yuill3, and Sergey V Smirnov3*
1 University of California, San Diego
2 University of London
3 University of Bath
* To whom correspondence should be addressed. E-mail: s.v.smirnov{at}bath.ac.uk.
Mitochondria are proposed to be a major oxygen sensor in hypoxic pulmonary vasoconstriction (HPV), a unique response of the pulmonary circulation to low oxygen tension. Mitochondrial factors including reactive oxygen species, cytochrome c, ATP and magnesium, are potent modulators of voltage-gated K+ (Kv) channels in the plasmalemmal membrane of pulmonary arterial smooth muscle cells (PASMCs). Mitochondria have also been found close to the plasmalemmal membrane in rabbit main PA smooth muscle sections. Therefore, we hypothesized that differences in mitochondria localization in rat PASMCs and systemic mesenteric arterial SMCs (MASMCs) may contribute to the divergent oxygen sensitivity in the two different circulations. Cellular localization of mitochondria was compared using immunofluorescent labelling, and differences in functional coupling between mitochondria and Kv channels was evaluated with the patch-clamp technique using specific mitochondrial inhibitors, antimycin A (acting at Complex III of the mitochondrial electron transport chain) and oligomycin A (which inhibits the ATP synthase). It was found that mitochondria were located significantly closer to the plasmalemmal membrane in PASMCs compared to MASMCs. Consistent with these findings, the effects of the mitochondrial inhibitors on Kv currents were significantly more potent in PASMCs than in MASMCs. The cytoskeletal disruptor cytochalasin B (10 µM) also altered mitochondrial distribution in PASMCs and significantly attenuated the effect of antimycin A on the voltage-dependent parameters of IKv. These findings suggest a greater structural and functional coupling between mitochondria and Kv channels specifically in PASMCs, which could contribute to the regulation of pulmonary arterial excitability in HPV.
