RESPONSES TO FIELD STIMULATION OF THE SMOOTH MUSCLE CELL MEMBRANE OF THE GUINEA PIG STOMACH

The responses of smooth muscle cell membrane of the guinea-pig stomach to field stimulation were investigated. In response to a single field stimulation (0.1-0.2 msec), the longitudinal and circular muscles excised from the antrum of the stomach produced a small hyperpolarization which was blocked by treatment with tetrodotoxin. Repetitive stimulation at various frequencies lowered the amplitude of the slow potential change thus causing suppression of the spike generation and mechanical response. Phentolamine did not suppress the generation of the inhibitory junction potential produced by a single stimulation but did slightly suppress the hyperpolarization produced by repetitive stimulation. Tetrodotoxin suppressed the amplitude but not the frequency of the slow potential change, however repetitive field stimulation in the presence of tetrodotoxin did not reduce further the amplitude of the slow potential changes. After a single or repetitive field stimulation was applied, the muscle membrane produced a delayed excitation on the slow potential change. The delayed excitation, however, did not generate in the presence of tetrodotoxin or of atropine. Reversal level for the inhibitory junction potential was ranged between--80 and--85 mV. Externally applied noradrenaline and ATP suppressed the generation of slow potential changes. Noradrenaline slightly hyperpolarized the membrane and increased the ionic conductance of the membrane but ATP neither modified the membrane potential nor increased the ionic conductance of the membrane.