The effect of insulin on the kinetics of pentose permeation of the rat heart.

1. The kinetics of permeation of pentoses into the rat heart in the presence of insulin are similar in nature to those in the absence of insulin.2. The half-saturation concentration of the carrier system is increased by insulin in a manner which is independent of insulin concentration.3. The V(max) of the carrier system is altered by insulin in a graded fashion: at low insulin concentrations it may be lower than in the absence of insulin.4. It is shown that these effects can be accounted for if insulin combines with the carrier and thereby increases either the rate constant governing the mobility of the carrier in the membrane or the rate constant governing dissociation of the sugar-carrier complex.5. The effects cannot be accounted for by a graded action of insulin on the membrane as distinct from the carrier.