ATP is released from rabbit urinary bladder epithelial cells by hydrostatic pressure changes–possible sensory mechanism?

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Abstract
1 The responses of rabbit urinary bladder to hydrostatic pressure changes and to electrical stimulation have been investigated using both the Ussing chamber and a superfusion apparatus. These experiments enabled us to monitor changes in both ionic transport across the tissue and cellular ATP release from it. 2 The urinary bladder of the rabbit maintains an electrical potential difference across its wall as a result largely of active sodium transport from the urinary (mucosal) to the serosal surface. 3 Small hydrostatic pressure differences produced by removal of bathing fluid from one side of the tissue caused reproducible changes in both potential difference and short-circuit current. The magnitude of these changes increases as the volume of fluid removed increases. 3 Amiloride on the mucosal (urinary), but not the serosal, surface of the membrane reduces the transepithelial potential difference and short-circuit current with an IC50 of 300 nm. Amiloride reduces the size of, but does not abolish, transepithelial potential changes caused by alterations in hydrostatic pressure. 4 Field electrical stimulation of strips of bladder tissue produces a reproducible release of ATP. Such release was demonstrated to occur largely from urothelial cells and is apparently non-vesicular as it increases in the absence of calcium and is not abolished by tetrodotoxin. 5 It is proposed that ATP is released from the urothelium as a sensory mediator for the degree of distension of the rabbit urinary bladder and other sensory modalities.