CONTRIBUTION OF P-2-PURINOCEPTORS TO NEUROGENIC CONTRACTION OF RAT URINARY-BLADDER SMOOTH-MUSCLE

1 The contribution of P-2-purinoceptors to neurogenic contraction was investigated in rat urinary bladder smooth muscle by measurement of isotonic tension. 2 Contraction of rat urinary bladder smooth muscle induced by electrical stimulation was decreased to 84.19+/-3.90% of the control (n=16) in the presence of atropine (1 mu M), which was further decreased to 38.80+/-2.75% of the control (n=49) in the presence of both atropine and 10 mu M alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-Me ATP). 3 The contractile response induced by electrical stimulation in the presence of atropine and alpha,beta-Me ATP was decreased to 27.81+.-4.07% (n=23) and 26.63+/-5.01% (n=15) of the control, by the addition of 100 mu M cibacron blue 3GA and 100 mu M suramin, respectively. The application of 100 mu M adenosine 5'-o-2-thiodiphosphate (ADP beta S) in the presence of atropine and alpha,beta-Me ATP decreased the contractile response induced by electrical stimulations to 17.15+/-3.71% (n=15) of the control. 4 Pretreatment of muscle strips with 100 mu M ADP beta S significantly reduced the response to either 200 mu M alpha,beta-methylene adenosine 5'-diphosphate or 200 mu M ADP beta S. 5 Uridine 5'-triphosphate (100 mu M to 1 mM) concentration-dependent ly contracted muscle strips, and this contraction was significantly antagonized by desensitization of P-2-receptors with alpha,beta-Me ATP (10 mu M), and completely antagonized by pretreatment of muscle strips with both alpha,beta-Me ATP and ADP beta S (100 mu M). 6 Di(adenosine-5') tetraphosphate (30 and 100 mu M) contracted muscle strips, whereas it failed to contract after desensitization of P-2-receptors. 7 It is suggested that about 20% of the neurogenic contraction of rat urinary bladder smooth muscle is mediated via ADP beta S-sensitive purinoceptors.