Potentiation of potassium currents by beta-adrenoceptor agonists in human urinary bladder smooth muscle cells: A possible electrical mechanism of relaxation

Jun Takemoto, Haruko Masumiya, Kazuo Nunoki, Takeya Sato, Haruo Nakagawa, Yoshihiro Ikeda, Yoichi Arai, Teruyuki Yanagisawa

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

We examined the effects of β-adrenoceptor agonists on the membrane currents of smooth muscle cells from the human urinary bladder using a whole-cell patch clamp to investigate the involvement of Ca2+- activated K+ (KCa) channels in relaxation by β-adrenergic agonists. With 0.05 mmol/l EGTA in the patch pipette, depolarizing pulses evoked outward rectifying currents. Isoproterenol (1 μmol/l) significantly increased the membrane currents by 75% at +80 mV with 0.05 mmol/l EGTA pipette solution. BRL 37344 (1 μmol/l) significantly increased the membrane currents by 44% at +80 mV. Iberiotoxin (100 nmol/l) significantly decreased the membrane currents by 60% at +80 mV. In the presence of iberiotoxin, the potentiation of the outward currents by isoproterenol was greatly suppressed and, in the presence of iberiotoxin and apamin (1 μmol/l), the potentiation by isoproterenol was totally abolished. On the other hand, with 5 mmol/l EGTA pipette solution, depolarizing pulses evoked smaller outward currents. Isoproterenol (1 μmol/l) did not change the membrane currents with 5 mmol/l EGTA pipette solution. The real-time PCR analysis revealed the expression of β2-adrenoceptors in the cells. These results suggest that Ca2+-activated and iberiotoxin- and apamin-sensitive currents via both large-conductance and small-conductance KCa channels could be increased by stimulation of β2-adrenoceptors.

Original languageEnglish
Pages (from-to)251-258
Number of pages8
JournalPharmacology
Volume81
Issue number3
DOIs
Publication statusPublished - 2008 Mar

Keywords

  • Apamin
  • BRL 37344
  • Ca-activated K (K) channels
  • Iberiotoxin
  • Patch clamp, whole-cell

ASJC Scopus subject areas

  • Pharmacology

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