Glutamine distribution in mitochondria from normal and acidotic rat kidneys

Mitochondria from control and acidotic rat renal cortex were incubated with labeled compounds to determine the distribution of L-glutamine. The mitochondrial preparations lacked detectable phosphate-independent glutaminase activity. In control mitochondria, the distribution of glutamine exceeded that of mannitol by 8% without an added energy source in the medium and by 9.9% when tetramethyl-p-phenylenediamine (TMPD) and ascorbate were present. The distribution of D-ribose (MW 150) was similar to that of L-glutamine (MW 146), indicating that these molecules penetrate into a slightly larger space than D-mannitol (MW 182). Inhibition of phosphate-dependent glutaminase activity with 5 mM glutamate did not alter the volume of glutamine distribution. In mitochondria from chronically acidotic rats, the glutamine/mannitol ratio was 1.03 in the absence of an energy source. With an energy source this ratio fell to 0.88 due to metabolism of glutamine during the separation process. Inhibition of glutamine metabolism with glutamate or alpha-ketoglutarate resulted in distribution ratios of 1.07 and 0.97, respectively. It is concluded that, although glutamine/mannitol ratios greater than 1.00 can be demonstrated in rat kidney mitochondria, such a finding may arise from causes other than the presence of free glutamine in the matrix space. Thus, it has yet to be established whether the inner membrane carrier for glutamine releases glutamine or glutamate into the matrix space.