Non-neuronal acetylcholine and urinary bladder urothelium

Non-neuronal release of acetylcholine (ACh) has been proposed to play a role in urinary bladder function. These studies investigated the expression and function of the non-neuronal cholinergic system in cultured urothelial cells isolated from the rat urinary bladder. Our findings have revealed that urothelial cells express the high-affinity choline transporter (CHT1) and acetylcholine-synthesizing enzymes, choline acetyltransferase (ChAT) and carnitine acetyltransferase (CarAT). In contrast to neurons, urothelial cells do not express the vesicular acetylcholine transporter (VAChT) but do express OCT3, a subtype of polyspecific organic cation transporter (OCT) that is thought to be involved in the release of acetylcholine from non-neuronal cells. Following exposure of cultured urothelial cells to 3H-choline, radioactivity was detected in the cells and increased release of radioactivity into the eternal media was evoked by mechanical stimulation (exposure of the cells to 50% hypotonic Krebs) or chemical stimulation of purinergic receptors by 100 μM ATP. The present experiments did not establish if the evoked release of radioactivity (termed 3H-ACh release in this paper) was due to release of acetylcholine or choline. 3H-ACh release was not evoked by application of acetylcholine alone, however pretreatment with the non-selective muscarinic receptor antagonist atropine prior to application of acetylcholine facilitated 3H-ACh release, suggesting that the acetylcholine released from urothelial cells may participate in a negative feedback mechanism by acting on muscarinic receptors to inhibit its own release in the urothelium. Brefeldin, an agent which disrupts vesicular exocytosis, did not block hypotonic-evoked 3H-ACh release. These observations indicate that acetylcholine release from urothelial cells is mediated by different mechanisms than those such as vesicular storage and exocytosis that underlie the release of neurotransmitters from nerves.