Endocrinology, Vol 109, 1775-1777, Copyright © 1981 by Endocrine Society

ARTICLES

Insulin-induced alterations in the lactoperoxidase-catalyzed radioiodination of membrane proteins of the toad bladder epithelium

WN Scott, SL Slatin, MH Cobb and IM Reich

Insulin-stimulated sodium transport in the toad urinary bladder consists of two components, a brief element of rapid onset that is independent of protein synthesis, and a sustained increase, slower in onset, that is dependent upon RNA and protein synthesis. The mucosal epithelium of the toad bladder was labeled by lactoperoxidase-catalyzed radioiodination (125I) following 15 min and 3 h exposure to insulin. The membrane of "mitochondria-rich" and "granular" mucosal cells from these tissues were analyzed by electrophoresis in SDS-urea. Compared to untreated tissues, membranes of "granular" mucosal cells from tissues exposed to insulin for 15 min contained a band (Mr = 15,000) with significantly increased labeling. Bladders exposed to insulin for 3 h showed no consistent increase in labeling. These data suggest that there are differences in the conformation of apical membrane proteins during the two phases of hormone-induced sodium transport. The technique may also offer an opportunity to identify "effector" proteins mediating this and other insulin responses.

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