Abstract
Electrophoretic cation permeability, as estimated by rates of passive swelling of mitochondria suspended in Na+ and K+ nitrate, increases with increasing temperature and elevated pH and is inhibited by Mg+ 2. Mitochondria swollen in Na+ nitrate at 37° and pH 8.2 contract in an energy-dependent reaction. The efficiency of the contraction (absorbance change per O 2 or ATP consumed) decreases with increased electrophoretic cation permeability as established by either elevated pH or addition of gramicidin. Efficiency is increased by Mg+ 2. This inverse relationship between electrophoretic cation permeability and efficiency of contraction is compatible with an osmotic contractile mechanism which depends on the Na + H + exchanger present in the mitochondrial membrane.
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