SOME PERMEABILITY PROPERTIES OF ISOLATED RAT LIVER CELL MITOCHONDRIA

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Abstract
The rates of diffusion of Na, K, sucrose, and I131-labeled albumin into mitochondria were measured. Na, K and sucrose were observed to enter mitochondria until an equilibrium concentration was reached. The diffusion of these solutes, after the first few minutes, followed the predicted diffusion curve for solutes entering a particle through a rate-limiting membrane with instantaneous mixing in the interior. At pH 7.4 Na and K entered more rapidly than sucrose. By increasing the pH to 8.0 the rate of Na penetration was reduced. I131 -labeled albumin entered very slowly, if at all. The rate of diffusion of sucrose into mitochondria was considerably less than the calculated rate of diffusion of sucrose into a sphere of water of the same size. It is concluded that the rate of diffusion of solutes between the external medium and the interior of the mitochondria is probably restricted and controlled by a mitochondrial membrane exhibiting passive permeability charactertics.