Metabotropic Signal Transduction for Bradykinin in Submucosal Neurons of Guinea Pig Small Intestine

Intracellular recording methods with "sharp" microelectrodes were used to study signal transduction mechanisms underlying the excitatory action of bradykinin (BK) in morphologically identified neurons in the small intestinal submucosal plexus. Exposure to BK evoked slowly activating membrane depolarization and enhanced excitability associated with increased input resistance in AH-type and decreased input resistance in S-type neurons. Preincubation with pertussis toxin did not affect the BK-evoked responses. Pretreatment with the cyclooxygenase inhibitors indomethacin or piroxicam suppressed or abolished the BK-evoked responses. Application of prostaglandin (PG) E₂ or PG analogs evoked BK-like depolarizing responses in the submucosal plexus with a potency order of PGE₂ > PGE₁ > 17-phenyl trinor-PGE₂ > PGI₂ > sulprostone > PGF_2α. Depolarizing responses to bradykinin or PGE ₂ in S-type neurons were suppressed in the presence of the phospholipase C inhibitor U73122 [(1-6-[([17β ]-3-methoxyestra-1,3,5[10]-tren-17-71)amino]hexyl)-1H-pyrrole-2,5-dione)], but not the inactive analog U73343 [(1-6-[([17β ]-3-methoxyestra-1,3,5[10]trien-17yl)amino]hexyl)-2,5-pyrrolidinedione)]. The inositol-1,4,5-trisphosphate receptor antagonist 2-aminoethoxydiphenylborane and the calmodulin inhibitor W-7, but not ryanodine, suppressed both bradykinin- and PGE₂-evoked responses. KN-62, an inhibitor of calmodulin kinases, or GF109203X, a specific protein kinase C inhibitor, suppressed both BK- and PGE₂-evoked depolarizing responses. Selective protein kinase A inhibitors did not alter BK- or PGE₂-evoked depolarizing responses in S neurons. The results suggest that BK stimulates synthesis and release of PGE₂, which acts at EP₁ receptors to evoke depolarizing responses in submucosal neurons. The postreceptor transduction cascade includes activation of phospholipase C, inositol-1,4,5-trisphosphate production, intraneuronal Ca2+ mobilization, activation of protein kinase C and/or calmodulin kinases, and phosphorylation of cationic channels.