Functional effects of the purinergic innervation of the rabbit urinary bladder

Although it is generally agreed that micturition is primarily under the control of the parasympathetic nervous system, there is good evidence that an atropine insensitive, nonadrenergic-noncholinergic neuronal component exists. Recent evidence indicates that the purinergic transmitter ATP (or an other purinergic analog) may be responsible for the atropine-insensitive portion of the contraction. Although isolated muscle strip studies have identified the purinergic response, the functional significance of this response has not been determined. Utilizing an in vitro whole-bladder model, we have investigated the functional ability of the purinergic component of field stimulation to empty the bladder under standard conditions. The results indicate: the response of the bladder to both cholinergic stimulation and field stimulation is characterized by a rapid rise in intravesical pressure followed by a prolonged plateau phase; expulsion of fluid from the bladder occurs primarily during the plateau phase of the contraction; in the presence of atropine, field stimulation produces only a transient rapid rise in tension, similar to the response to exogenous ATP; and this "purinergic" response does not result in significant bladder emptying. These results suggest that the bladder response to this purinergic stimulation may be complimentary to, but functionally different from that which occurs in response to cholinergic transmission alone.