Studies on the electrical stimulation-induced contractile responses of hamster and mouse gallbladders

Isolated gallbladders of both hamsters and mice showed a contractile response consisting of initial and secondary contractile responses to electrical stimulation with rectangular pulses (50 volt, 40 Hz) of 6 msec duration for a period of 10 seconds. The duration time of the contractile response was very long. This was because the duration time of the process of the initial contractile response was as short as 5 to 40 seconds, but that of the secondary contractile response was as long as 8 to 15 minutes. Both initial and secondary contractile responses of the gallbladder in both hamsters and mice were little affected by atropine (1 x 10(-6)M, guanethidine (1 x 10(-6) M) and tetrodotoxin (1 x 10(-7) M). In both animals, further, the initial contractile response of the gallbladder was little affected by indomethacin (1 x 10(-5) M) and 5, 8, 11, 14-eicosatetraynoic acid (ETYA) (5 x 10(-6) g/ml), while the amplitude of the secondary contractile response of the gallbladder was significantly reduced by such drugs. From these results, we obtain the following conclusions: 1) In both animals, the intramural nerves of the gallbladder may have no influence on the both initial and secondary contractile responses of the gallbladder. 2) The initial contractile response is probably mediated by a direct effect of the electrical stimulation to the muscle in the wall of the gallbladder, while the secondary contractile response is probably attributable to prostaglandins released from the wall of the gallbladder by a direct effect of the electrical stimulation to the wall.