A central function of urinary bladder smooth muscle (UBSM) is the translation of neural inputs into a normal micturition response, a function that is dramatically altered with outlet obstruction. This proposal focuses on how these neural inputs through cholinergic and purinergic pathways differentially impact calcium (Ca2+) signal patterning in UBSM, and on electrical and contractile responses under normal conditions and with partial outlet obstruction. Despite the importance of these pathways, major gaps remain in our knowledge o1 the underlying nerve-evoked excitation-contraction (E-C) coupling mechanisms and the changes that occur with obstruction. In a major advance, we have been able to measure, with high spatial and temporal resolution, nerve excitation, and local Ca2+ signals in intact whole urinary bladders and bladder strips. We have identified two distinct local calcium transients in UBSM: 1) nerve-evoked calcium transients, mediated through purinergic receptors, and 2) the local release of calcium from the sarcoplasmic reticulum (SR) through ryanodine receptors (RyRs).
Aim 1 seeks to elucidate the novel mechanisms by which UBSM decodes cholinergic and purinergic stimulation into different calcium signals, which differentially depend on Ca2+ entry through voltage-dependent calcium channels (VDCC), inositol triphosphate receptors (IP3Rs) and RyRs in the SR.
Aim 2 focuses on UBSM E-C coupling mechanisms in response to the unique calcium signals elicited by cholinergic and purinergic mechanisms.
In Aim 3, we explore the interaction of VDCC and SR Ca2+ load in mediating cholinergic and purinergic excitation in normal and dysfunctional bladders. The hypothesis that SR dysfunction following outlet obstruction differentially affects cholinergic and purinergic stimulation by altered UBSM calcium signaling will be tested. Using state-of-the-art techniques, genetically altered mice, and our recently developed mouse model of partial bladder outlet obstruction, the proposed study will provide new insights into the differential impact of cholinergic and purinergic pathways on UBSM in normal and obstructed bladders. The novel findings of this study will be highly relevant to understanding fundamental mechanisms of nerve-evoked E-C coupling in UBSM, and identify key elements that underlie bladder dysfunction, and as such should be highly relevant to the understanding and treatment of bladder dysfunction.
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