Effect of buffers and osmolality on anion uniport across the mitochondrial inner membrane

The effects of buffers and osmolality of the suspending medium on the pH-dependent anion uniport across the inner membrane of isolated rat liver mitochondria have been studied using the LIGHT scattering technique to measure passive osmotic swelling. In contrast to some other transport processes the rates of entry of chloride and other anions via the anion-conducting channel decreased steeply with increasing solute concentration. This effect appears to be a result of increased osmolality or decreased matrix volume rather than inhibition by the anion since it was also produced by increasing the osmolality by addition of non-penetrant solutes. The effects of some pH buffers on the mitochondrial anion-conducting channel were also investigated. Some zwitterionic buffers had little effect other than that produced by increasing osmolality but Tricine, Popso and Caps produced marked additional inhibition of anion uniport and several other zwitterionic buffers were also inhibitory. The correlation between increased anion conductivity and increased matrix volume supports the proposal that this channel functions in regulation of the volume of the mitochondrial matrix.