title: Large-conductance calcium-activated potassium channel activity, as determined by whole-cell patch clamp recording, is decreased in urinary bladder smooth muscle cells from male rats with partial urethral obstruction.
abstract: OBJECTIVE
  To examine the effect of partial urethral obstruction (PUO) on bladder smooth muscle outward potassium current and the contribution of the large-conductance calcium-activated potassium (Maxi-K, BKCa) channel to this activity in smooth muscle cells isolated from bladders of sham-operated and PUO male rats using whole-cell patch clamp recording techniques. To determine the effect of PUO on the expression of the Maxi-K channel α and β1 subunits and in vitro detrusor contractility.
  
  
  METHODS
  Twenty adult male Sprague-Dawley rats were divided equally into two groups and subjected to surgical ligation of the urethra (PUO) or sham surgery (SHAM). After 2 weeks, the detrusors from PUO and SHAM rats were used for molecular analyses (mRNA and protein quantification of Maxi-K subunits) or organ bath contractility studies, or myocytes were isolated for conventional whole-cell patch clamp analyses.
  
  
  RESULTS
  PUO increased bladder mass 2.5-fold and detrusor strips exhibited a more tonic-type contraction and increased contractility compared with controls (SHAM). Iberiotoxin (300 nM) sensitive Maxi-K channel current comprised about 40% of the outward whole-cell current in SHAM bladders but only about 8% in PUO bladders. Expression of the α subunit of the Maxi-K channel was significantly decreased ~40% while the expression of the β1 subunit was increased ~2-fold at the mRNA level. The increase in β1 expression was confirmed by Western blotting.
  
  
  CONCLUSIONS
  Our findings show that obstruction of the rat bladder is associated with decreased Maxi-K channel activity of bladder smooth muscle cells, determined via direct current measurement. Increased expression of the β1 subunit points to a compensatory reaction to decreased Maxi-K channel activity. Maxi-K channel openers or gene therapy may therefore provide therapeutic benefit for the overactive bladder.
authors.affiliation: Department of Urology, Albert Einstein College of Medicine, New York, New York, USA.
authors.forename: Memduh
authors.initials: M
authors.lastname: Aydin
authors.forename: Hong Zhan
authors.initials: HZ
authors.lastname: Wang
authors.forename: Xinhua
authors.initials: X
authors.lastname: Zhang
authors.forename: Rowena
authors.initials: R
authors.lastname: Chua
authors.forename: Keith
authors.initials: K
authors.lastname: Downing
authors.forename: Arnold
authors.initials: A
authors.lastname: Melman
authors.forename: Michael E
authors.initials: ME
authors.lastname: DiSanto
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000502:physiology*; D008297:Male; D032389:Myocytes, Smooth Muscle / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D014524:Urethral Obstruction / Q000503:physiopathology*; D001743:Urinary Bladder / Q000503:physiopathology*
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels