[A calcium channel in the rat liver inner mitochondrial membrane. Effective diameter and selectivity under various...

The pore with an effective diameter of 6.0 A is a Ca(2+)-channel of the inner mitochondrial membrane. Transport of nonelectrolytes through the pore is inhibited by ruthenium red, a specific Ca2+ transport inhibitor, and by polyanions which bind to the positively charged regions in the pore localized on the outer side of the inner mitochondrial membrane. The selectivity of Ca2+ ion transport into intact mitochondria is due to the binding of Ca2+ ions by the glycoprotein at the mouth of the pore as well as to electrostatic interactions of monovalent cations (electrostatic repulsion) and Cl- ions (strong binding) with the positively charged region of the ion-selective filter of the pore. Under normal conditions SCN- and NO3- ions are transferred through the pore at a high rate. Removal of Mg2+ ions and the rise in pH diminish the electrostatic repulsion of the monovalent cations and Cl- ions from the positively charged region of the pore. Depending on conditions, the pore can function as a monovalent ion transport system or as a mechanism of Cl- ion transfer through the inner mitochondrial membrane.