The K+ATP channel is involved in a low-amplitude permeability transition in plant mitochondria

Pea (Pisum sativum) stem mitochondria, energized by NADH, succinate or malate plus glutamate, underwent a spontaneous low-amplitude permeability transition (PT), which Could be monitored by dissipation of the electrical potential (DeltaPsi) or swelling. The occurrence of the latter effects was dependent on O-2 availability, because O-2 shortage anticipated the manifestation of both DeltaPsi dissipation and swelling. Spontaneous DeltaPsi collapse was also monitored in sucrose-resuspended mitochondria and again O-2 deprivation caused an anticipation of the phenomenon. However, in this case A P dissipation was not accompanied by a parallel mitochondrial swelling. The latter effect was, indeed, evident only if mitochondria were resuspended in KCl (as osmoticum), or other cations with a molecular mass up to 100 Da (choline(+)). PT was also induced by protonophores (carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) or free fatty acids) or valinomycin (only in KCl). The FCCP-induced dissipation of DeltaPsi and swelling were inhibited by ATP and stimulated (anticipated) by cyclosporin A or O-2 shortage. The FCCP-induced PT was accompanied by the release of pyridine nucleotides from the matrix and of cytochrome c from the intermembrane space of KCl-resuspended mitochondria. The spontaneous and FCCP-induced low-amplitude PT of plant mitochondria are interpreted as due to the activity of a recently identified K-ATP(+) channel whose open/closed state is dependent on polarization of the inner membrane and on the oxidoreductive state of some sulfhydryl groups. (C) 2004 Elsevier B.V. and Mitochondria Research Society. All rights reserved.