Expression and Distribution of the Sweet Taste Receptor Isoforms T1R2 and T1R3 in Human and Rat Bladders

Purpose: Artificial sweeteners augment bladder contraction. We hypothesized that artificial sweeteners activate sweet taste receptors in the bladder. Thus, we investigated the expression of sweet taste receptors in human and rat bladders. Materials and Methods: Sections of human and rat bladders were cut from paraffin blocks and stained by immunohistochemistry for the expression of T1R2/3 sweet taste receptors. Bladder homogenates were subjected to sodium dodecyl sulfate-polyacrylamide electrophoresis, followed by immunoblotting for T1R2/3 receptor expression. Rat bladder strips with and without urothelium were suspended in organ baths. The contractile response to 10 Hz electrical field stimulation was determined in the absence and presence of saccharin (Sigma-Aldrich (R)) (10(-8) to 10(-3) M). Responses to KCl in the absence and presence of saccharin, and saccharin plus zinc were also determined. Results: T1R2/3 sweet taste receptors were expressed in human and rat bladder urothelium. Immunostaining was evident in the plasma membrane of the 3 urothelial cell types, particularly umbrella cells. Immunoblotting revealed bands at expected molecular weights in human and rat bladder homogenates. Saccharin augmented rat bladder smooth muscle contraction due to electrical field stimulation only when urothelium was present in the bladder strip. Zinc blocked the enhancing effect of saccharin on responses to KCl. Conclusions: T1R2/3 sweet taste receptors are expressed in human and rat bladder urothelium. Activation of these receptors by artificial sweeteners may result in augmented bladder contraction.