Contractile responses to electrical field stimulation and ATP in guinea-pig urinary bladder

1. The responses of guinea-pig urinary bladder smooth muscle to intramuscular nerve stimulation were investigated by isometric tension recording. 2. The nerve mediated contractions, evoked by field stimulation with a stimulus of 0.5 msec duration, a frequency of 15 Hz and a voltage of 50 V, were inhibited by atropine (10(-6) M) and alpha, beta-MeATP (10(-4) M) to about 80% and 20%, respectively, of control. 3. Simultaneous application of atropine (10(-6) M) and alpha, beta-MeATP (10(-4) M) abolished the contraction evoked by selective nerve stimulation. 4. Terodiline (10(-4) M), one of Ca2+ antagonists, inhibited the contraction evoked by both nerve selective stimulation and exogenously applied ATP. 5. Based on these results we suggested that in guinea-pig urinary bladder, ATP was a predominant excitatory transmitter and the nerve-mediated contraction and exogenous ATP were mainly dependent upon Ca2+ influx.