Hypertrophy changes the muscarinic receptor subtype mediating bladder contraction from M₃ toward M₂

Abstract

Hypertrophy changes the muscarinic receptor subtype mediating bladder contraction from M3 toward M2. Am J Physiol Regul Integr Comp Physiol 285: R701-R708, 2003. First published May 22, 2003 10.1152/ajpregu.00009.2003.-Major pelvic ganglion electrocautery (MPGE) and spinal cord injury in the rat induce bladder hypertrophy and a change in muscarinic receptor subtypes mediating bladder contraction from predominantly M 3 to a combination of M2 and M3. To determine whether this is a result of bladder hypertrophy or denervation, we studied the following groups: sham-operated controls, urinary diversion (DIV), MPGE together with urinary diversion (DIV-DEN), bilateral MPGE (DEN), bladder outlet obstruction (BOO), and MPG decentralization (MPG-DEC). The degree of bladder denervation was determined by the maximal carbachol response normalized to the response to electric field stimulation. Receptor subtype density was determined by immunoprecipitation. The affinity of subtypeselective muscarinic antagonists for inhibition of carbacholinduced contractions was used to determine the subtypemediating contraction. DEN, MPG-DEC, and BOO bladders were hypertrophic whereas DIV bladders were atrophic compared with sham operated. Bladder contraction in shamoperated, DIV, and DIV-DEN was mediated by the M3 receptor subtype, whereas the M 2 subtype participated in contraction in the DEN, MPG-DEC, and BOO groups. The hypertrophied bladders had an increase in total and M 2 receptor density while all experimental groups showed a reduction in M3 receptor density. Thus bladder hypertrophy, independent from bladder denervation, causes a shift in the muscarinic receptor subtype mediating bladder contraction from M3 toward M2. denervation; outlet obstruction; urinary diversion PHARMACOLOGICAL DATA, based on the actions of subtypeselective antimuscarinic agents, can distinguish four subtypes of muscarinic acetylcholine receptors (M 1 -M 4 ). Molecular techniques have identified five muscarinic receptor subtypes (M 1 -M 5 ) arising from five separate genes (7,8). Both M 2 and M 3 muscarinic receptor subtypes are found in most smooth muscles. The M 2 receptor preferentially couples to the inhibition of adenylyl cyclase through the G i family of proteins, while the M 3 receptor preferentially couples to IP 3 generation and calcium mobilization through the G q family of proteins (7,8). Pertussis toxin (PTX), which ADP ribosylates and therefore inactivates the G i family of proteins, has no apparent effect on contraction (23). Even though the M 2 muscarinic receptor density is greater than the M 3 receptor density in bladder and other smooth muscles, the affinity of subtype-selective muscarinic receptor antagonist drugs indicates that contraction is mediated by the M 3 receptor in most smooth muscles under normal conditions (7,9).A number of studies have shown that under certain conditions the M 2 receptor subtype can contribute to the contractile response. This includes selective alkylation of M 3 receptors in an environment of increased intrac...

The Loss and Progressive Recovery of Voiding after Spinal Cord Interruption in Rats is Associated with Simultaneous Changes in Autonomous Contractile Bladder Activity

“…In decentralised rat bladders an enhanced and direct contractile role for M 2 has been reported [19]. Similar results were found in obstructed [22] and neurogenic [3,23] rat bladders. The weak M 2 -preference of ABET might then be partially responsible for the increased contractile effects of ABET on ACA in bladders post-SCI, if these bladders indeed have an enhanced M 2 -function.…”

“…The observed increase in M 2 mRNA is likely to correlate with an elevated expression of M 2 receptors since an increased density of M 2 protein has been reported in decentralised [19], obstructed [22], and neurogenic [23] rat bladders. The behaviour of M 3 mRNA in bladders post-SCI seems to correlate less with the expression of M 3 protein since in hypertrophied [22] and (spontaneous voiding) neurogenic [23] rat bladders a decrease of M 3 protein amount has been reported. Similar noncorrelating findings have been reported before [26] and suggest differences in the cascade from mRNA to protein between M 2 and M 3 .…”

Human Idiopathic and Neurogenic Overactive Bladders and the Role of M2 Muscarinic Receptors in Contraction

“…One group has suggested that M 2 receptors contribute to direct detrusor contraction in the denervated, non-voiding spinal injured rat and the obstructed rat [8,9,27], whilst others could find no evidence of a change in receptor function in the obstructed rat [28]. In the present study patients with neurogenic overactivity due to spinal injury were able to void and in these patients detrusor contraction remained mediated by the M 3 receptor.…”

M2 mediated contractions of human bladder from organ donors is associated with an increase in urothelial muscarinic receptors

“…A number of experimental conditions in the rat are associated with an increased contribution of the M 2 receptor subtype to the contractile response. These include sarcoplasmic reticulum calcium depletion with thapsigargin [Braverman et al, 2002], bladder denervation [Braverman et al, 1999;Braverman and Ruggieri, 2003;Ruggieri and Braverman, 2006], spinal cord injury [Braverman et al, 1999], bladder decentralization [Braverman and Ruggieri, 2003], and bladder outlet obstruction [Braverman and Ruggieri, 2003;Ruggieri and Braverman, 2006]. It is unclear if previous bladder hypertrophy, neurogenic lesions, or bladder over activity symptoms were present in the medical history of bladder donors based on the limited information available from the organ procurement agency.…”

“…M 2 receptors have been shown to play an indirect role in detrusor contraction by inhibiting bladder smooth muscle relaxation and enhancing detrusor contraction via G i inhibition of cAMP levels [Ehlert et al, 2005]. In pathologic states, the M 2 receptor pathway has a greater role in mediating contraction in rats and humans [Braverman and Ruggieri, 2003;Pontari et al, 2004;Gevaert et al, 2006]. Thus, with pathophysiological stressors, the mechanisms that transduce the muscarinic contractile signal can become altered such that the M 2 receptor subtype plays a more prominent role in the contractile response that is normally mediated by the M 3 receptor subtype.…”