1. The electrical properties of the longitudinal muscle of the guinea-pig fundus were investigated with the microelectrode method.
2. The membrane potential was -58.1 mV, the space constant of the membrane was 2.2 mm and the time constant of the membrane was 130 msec. The cable equations could be applied to this tissue.
3. When the current-voltage relation was observed by applications of weak inward and outward current pulses, the rectifying property of the membrane was observed.
4. Application of strong intensity of inward current pulses to the membrane produced an electrotonic potential with an initial transient phase which was gradually reduced in amplitude to a steady level. Application of outward. current pulses to the membrane produced an electrotonic potential which gradually increased in amplitude to a steady level.
5. Decrease and increase in amplitude of the electrotonic potential during application of strong inward and outward current pulses was mainly due to increased and decreased K-conductance of the membrane respectively, since the above effects were not influenced by either Na-free (tris) Krebs or NO₃- and C₆H₅SO₃- Krebs solution.
6. A spike of ‘all or none’ type could not be recorded from all muscle fibres but abortive spikes could often be recorded. Some of the muscle fibres did not produce an active response.
7. On treatment with TEA (3-5 mM), the rectifying property of the membrane was suppressed, and the generated spike was the ‘all or none’ type. The rate of rise of the spike was not affected, but the rate of fall of the spike was markedly reduced.
8. The conduction of excitation from the fundus to the pylorus was often incomplete. On treatment with TEA, conduction of the excitation was not decremental.
9. The physiological roles of the fundus of the stomach was discussed in relation to the properties of the muscle membrane.