Function, signal transduction mechanisms and plasticity of presynaptic muscarinic receptors in the urinary bladder.

Presynaptic M1 muscarinic receptors on parasympathetic nerve terminals in rat urinary bladder strips are involved in an autofacilitatory mechanism that markedly enhances acetylcholine release during continuous electrical field stimulation. The facilitatory muscarinic mechanism is dependent upon a PKC mediated second messenger pathway and influx of extracellular Ca2+ into the parasympathetic nerve terminals via L and N-type Ca2+ channels. Prejunctional muscarinic facilitation has also been detected in human bladders. The muscarinic facilitatory mechanism is upregulated in hyperactive bladders from chronic spinal cord transected rats; and the facilitation in these preparations is primarily mediated by M3 muscarinic receptors. Presynaptic muscarinic receptors represent a new target for pharmacological treatment of bladder hyperactivity. If presynaptic facilitation is restricted to the bladder and not present in other tissues then drugs acting at this site might be expected to exhibit uroselectivity.