Identification and characterization of an exercise-sensitive pool of XXXX transporters in skeletal muscle.

@entity575 @entity969 @entity2368 @entity1365 @entity11664 @entity413
Augmentation of @entity413 transport into skeletal muscle by @entity2368 translocation to the plasma and T-tubule membranes can be mediated independently by insulin and by contraction/exercise. Available data suggest that separable pools of intracellular @entity2368 respond to these two stimuli. To identify and characterize these pools, we fractionated skeletal muscle membranes in a discontinuous sucrose density gradient. Fractions of 32 and 36% @entity969 exhibited the highest enrichment of @entity2368 and were independently responsive to insulin and exercise, respectively. The combination of the two stimuli depleted both @entity2368 fractions simultaneously. Both vesicle populations contained the @entity11664 aminopeptidase, whose expression had previously been shown to be specific to muscle and fat and restricted to @entity2368 vesicles in the latter tissue. In muscle, @entity11664 translocates exactly as does @entity2368 in response to insulin and exercise. The contraction- and insulin-sensitive @entity2368 pools also contained secretory component-associated membrane protein/ @entity413 transporter vesicle triplet but not @entity1365 and caveolin. Immunoadsorption of the two pools followed by @entity575 staining did not reveal any obvious difference in their major protein components. On the other hand, sedimentational analysis in sucrose velocity gradients revealed that the insulin-sensitive @entity2368 vesicles had a larger sedimentation coefficient than the exercise-sensitive vesicles. Thus, the separation of the two intracellular @entity2368 pools should be useful in dissecting what are likely to be different signal transduction pathways that mediate their translocation to the cell surface.
