Effects of Insulin on Ribonucleic Acid Synthesis in Toad Urinary Bladder*

Abstract

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.