Abstract
The effects of Ba ion on the electrical activity of the guinea-pig antral smooth muscle were investigated with the double sucrose gap method.
1. Ba ion in the presence or absence of Na ion depolarized the membrane and increased the input resistance of the membrane.
2. The spontaneously generated spike was followed by a sustained depolar ization (plateau formation) which lasted more than one minute. Transitions of the membrane potential between the two levels (rest and plateau) appeared periodically.
3. The duration of the plateau depended on the membrane potential level.
4. The plateau formation required Na ion, since when Na ion was replaced with tris, chorine or sucrose, the spike but no plateau formation was observed.
5. Ba ion generated the spikes with plateaus in various concentrations of K ion (0.59-17.7 mM). With more than 29.5 mM K ion, the membrane was further depolarized and oscillatory spikes or depolarization block of the spike occurred.
6. Ba ion also produced the spike and plateau in solutions containing foreign anions.
7. The results led to the conclusion that Ba ion mainly inhibits the K-con ductance during the resting state, carries the current and delays the onset in K-conductance increase during the active state of the membrane.
