Our previous studies showed that bladder hypertrophy shifts the muscarinic receptor subtype mediating contraction from M3 towards M2 along with increased M2 and decreased M3 protein concentration. We quantified mRNA for M1 through M5 receptors to determine whether the changes in M2 and M3 protein levels was due to changes in transcription.
Bladder hypertrophy was induced by bladder outlet obstruction (BOO), major pelvic ganglion electrocautery (DEN), and major pelvic ganglion decentralization (DEC). Bladder atrophy was induced by ureteral diversion (DIV). Additional groups included denervated and diverted (DEN-DIV), sham operated (SHAM), and normal (NOR) controls. Transcripts were quantified using a multiplex ribonuclease protection assay (RPA) and receptor protein density was determined by immunoprecipitation. Receptor transcripts were expressed per unit total RNA.
Although all five receptor subtype transcripts were detected in all experimental groups, the densities of M1, M4, and M5 were much lower than for the M2 and M3 subtype. There were more M2 receptor transcripts than all the others, consistent with M2 protein determinations. M2 transcripts were significantly increased in DEN and BOO bladders. Surprisingly, M3 transcripts were also significantly increased in BOO. There was a significant correlation (r = 0.98, P < 0.001) between protein density and transcript density for the M2 but not the M3 receptor among the different experimental groups.
Changes in mRNA concentration are reflected by changes in protein density for the M2 receptor but not for the M3 receptor. Extrapolation of functional effects from transcript density data is invalid for M3 mediated bladder contractions. © 2005 Wiley-Liss, Inc.