Studies on the excitatory neurotransmission in the guinea-pig urinary bladder

The amplitude of atropine-resistant twich contractions of muscle strips of the guinea-pig urinary bladder was not changed after 90 min continuous electrical stimulation in the presence of 100 microM hemicholinium-3, as compared with the amplitude of the corresponding contractions in control experiments without hemicholinium-3. Addition of 100 microM choline to the medium did not change the amplitude of contractions either. Methionine-enkephalin (1 microM) known as a potent inhibitor of acetylcholine release in autonomic nerves did not change the amplitude of the twich responses. Apamin (1 microM) which inhibited the non-adrenergic, non-cholinergic responses in taenia coli did not change the amplitude of the atropine-resistant contractile responses of the guinea-pig urinary bladder. It is concluded that acetylcholine is not the principle excitatory neurotransmitter in the guinea-pig urinary bladder, although some cholinergic contribution to the twich response exists. The nonadrenergic, non-cholinergic atropine-resistant contractile response of the guinea-pig urinary bladder is apamin-resistant.