Permeability of Rat Liver Microsomes to Sucrose and Carboxypoly-glucose in vitro

A study was made of the permeability of the microsomes to C(14)-sucrose and to C(14)-carboxypolyglucose, a branch-chained glucose polymer with a molecular weight of approximately 50,000. It was concluded that the microsomal membranes are permeable to sucrose on the basis of the following evidence: the volume of distribution of C(14)-sucrose was 84 per cent of the total microsomal pellet water; the sucrose unavailable volume, the per cent dry weights of the microsomal pellets, and the optical density of microsomal suspensions were independent of the concentration of sucrose in the suspending medium. It is suggested that the microsomal water which is unavailable to sucrose may be bound to protein and/or ribonucleic acid of the microsomes. The volume of distribution of C(14)-carboxypolyglucose was 44 per cent of the total pellet water, and it is considered that the microsomal membranes may be impermeable to this compound. Pretreatment with ribonuclease resulted in small increases in the volumes of distribution of both C(14)-sucrose and C(14)-carboxypolyglucose.