The signalling pathway which causes contraction via P2‐purinoceptors in rat urinary bladder smooth muscle

Abstract

1. The signalling pathway which causes contractions to adenosine 5'-O-2-thiodiphosphate (ADPbetaS) and alpha,beta-methylene adenosine 5'-diphosphate (alpha,beta-Me ADP) was investigated in rat urinary bladder smooth muscle by measuring isotonic tension. 2. The responses to 10 microM alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-Me ATP) in 0 and 3.6 mM Ca2+ were 5.9+/-1.3 (n=10) and 122.2+/-6.4 (n=8) % respectively of those obtained in 1.8 mM Ca2+, whereas those to 100 microM ADPbetaS were 34.6+/-3.3 (n=8) and 96.8+/-7.2 (n = 8) %, in 0 and 3.6 mM Ca2+, respectively. In both experimental conditions, the responses to the two agonists expressed as % of the control responses were significantly different (P<0.01). 3. Indomethacin at high concentrations (>1 microM) decreased the responses to alpha,beta-Me ATP (10 microM), ADPbetaS (100 microM) and alpha,beta-Me ADP (100 microM). However, no significant difference was obtained between the responses to all the agonists at 30 microM indomethacin. 4. 2-Nitro-4-carboxphenyl n,n-diphenylcarbamate (NCDC) at concentrations between 1 microM and 100 microM concentration-dependently decreased the responses to ADPbetaS (100 microM) and alpha,beta-Me ADP (100 microM) and almost completely inhibited them at 100 microM. Although the responses to alpha,beta-Me ATP (10 microM) were also inhibited by the drug, at 50 and 100 microM NCDC the responses to alpha,beta-Me ATP were significantly larger than those to ADPbetaS and alpha,beta-Me ADP (P<0.01). 5.NCDC 100 microM significantly inhibited the KCl-induced contraction to 65.9+/-4.9% (n=6) of the control (P<0.01). 6. It is suggested that the contraction via ADPbetaS-sensitive receptors in the rat urinary bladder smooth muscle mainly depends on Ca2+ ions liberated from intracellular Ca2+ stores, though the contribution of Ca2+ ions from the extracellular space cannot be neglected. The release of Ca2+ ions from stores is mainly mediated by the production of inositol trisphosphate (IP3) via the activation of phospholipase C.