OBJECTIVE

To investigate the mechanism of bombesin-induced circular smooth muscle cell contraction in cat esophagus.

METHODS

Specific G protein or phospholipase C involved in cat esophagus contraction was identified, muscle cells were permeabilized with saponin. After permeabilization of muscle cells, the Gi3 antibody inhibited bombesin-induced smooth muscle cell contraction.

RESULTS

Incubation of permeabilized circular muscle cells with PLC-beta3 antibody could inhibit bombesin-induced contraction. H-7, chelerythrine (PKC inhibitor) and genistein (protein tyrosine kinase inhibitor) inhibited bombesin-induced contraction, but DAG kinase inhibitor, R59949, could not inhibit it. To examine which mitogen-activated protein kinase (MAPK) was involved in bombesin-induced contraction, the specific MAPK inhibitors (MEK inhibitor, PD98059 and p38 MAPK inhibitor, SB202190) were used. Preincubation of PD98059 blocked the contraction induced by bombesin in a concentration-dependent manner. However, SB202190 had no effects on contraction.

CONCLUSIONS

Bombesin-induced circular muscle cell contraction in cat esophagus is madiated via a PKC or a PTK-dependent pathway or p44/p42 MAPK pathway.