We previously found that the sustained rise in active sodium transport by the toad urinary bladder after exposure to insulin is associated with the synthesis of a membrane protein with a molecular weight of 25, 000. Studying the effects of insulin on the incorporation of uridine into RNA of epithelial cells of the bladder, we now report that insulin causes a 39% increase in the incorporation of [3H]uridine into poly(A)-containing RNA extracted from granular cells, the predominant epithelial cell type. The increased accumulation of label in RNA, most notably species ranging from 5-10S, could be demonstrated whether cells were pulsed with [3H]uridine or continuously exposed to the label. Using a reticulocyte lysate system, we compared the translation products of RNA from untreated and insulin-treated granular mucosal cells. Exposure to insulin was associated with the expression of a mRNA coding for a protein with molecular weight of approximately 25, 000, similar in size to the ins lin-induced membrane protein we previously identified in the intact tissue.(Endocrinology 109: 2167, 1981).
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