Action of Bradykinin in the Submucosal Plexus of Guinea Pig Small Intestine

Abstract

Intracellular recording methods with "sharp" microelectrodes were used to study actions of bradykinin (BK) on electrical behavior of morphologically identified neurons and the identification and localization of BK receptors in the submucosal plexus of guinea pig small intestine. Exposure to BK depolarized the membrane potential and elevated excitability in submucosal neurons with AH-type electrophysiological behavior and Dogiel II multipolar morphology and in neurons with S-type electrophysiological behavior and uniaxonal morphology. BK-evoked depolarizing responses were associated with increased neuronal input resistance in AH-type neurons and decreased input resistance in S-type neurons. -BK mimicked the excitatory action of BK. Western blot analysis and reverse transcription-polymerase chain reaction confirmed the expression of B 2 receptor protein and mRNA. Binding studies with a fluorescently labeled BK 2 antagonist found expression of B 2 receptors on a majority of the ganglion cells. B 2 receptors occupied 82% of the neurons that expressed immunoreactivity for neuropeptide Y, 75% of the neurons that expressed vasoactive intestinal peptide, 84% of the neurons that expressed substance P, 71% of the neurons that expressed choline acetyltransferase, and all neurons that expressed calbindin immunoreactivity. The results suggest that the B 2 receptor mediates the excitatory action of BK on submucosal plexus neurons. Pathophysiological significance of the excitatory actions on secretomotor neurons might be stimulated mucosal secretion and the secretory diarrhea associated with intestinal inflammatory states.Chemical signaling is a mode of physiological communication between the enteric nervous system (ENS) and the enteric immune system (Wood, 2002). Neural networks in the myenteric and submucosal plexuses of the ENS interact to form an independent integrative nervous system that controls intestinal motility, secretion, and blood flow and interact to organize the activity of each of the three effector systems into functional patterns of digestive behavior (Wood, 1994a;Gershon, 1998;Wood et al., 1999). In so doing, the ENS functions in interactive concert with the enteric immune system. Populations of immune/inflammatory cells (lymphocytes, granulocytes, and mast cells) surround the ENS and expand in number during pathological inflammatory states (e.g., enteric infections, inflammatory bowel disease, and radiation-induced enteritis). Members of the immune/inflammatory cell populations communicate with the ENS in paracrine manner through the release of chemical mediators (Frieling et al., 1994;Wood, 2002;Liu et al., 2003a). Exposure to the inflammatory mediators histamine, mast cell proteases, prostaglandins, leukotrienes, and cytokines modifies both neuronal excitability and neurotransmission (Nemeth et al., 1984;Frieling et al., 1994;Dekkers et al., 1997;Xia et al., 1999;Gao et al., 2002; Liu et al., 2003a,b).The present study was focused on bradykinin (BK) as one of the putative mediators formed during i...

Neurophysiological mechanisms of bradykinin-evoked mucosal chloride secretion in guinea pig small intestine

“…Results of our previous work on the cellular neurophysiology of secretomotor neurons suggested that stimulation of calmodulin-dependent protein kinase is involved in B2R-mediated excitation of secretomotor neurons [9] . We used W-7, a membrane permeable calmodulin inhibitor, and KN-62, a selective calmodulindependent protein kinase inhibitor, as pharmacological tools to test the hypothesis that stimulation of Isc by BK involved post-receptor activation of calmodulin-dependent protein kinase.…”

“…Our earlier studies on the mechanisms of post-receptor signal transduction using electrophysiological methods suggested that BK caused excitation of submucosal secretomotor neurons by activation of B2R on submucosal neurons, stimulation of a signal transduction pathway involving phospholipase C (PLC), elevation of intraneuronal IP3, and elevation of free cytosolic Ca 2+ [9] . These findings suggested that stimulation of PLC and intracellular IP3 would also underlie a component of the stimulatory action of BK on ΔIsc at the tissue level.…”

“…Previously, we demonstrated that B2R is expressed on a majority of the ganglion cells in the myenteric and submucosal plexuses in the small intestine of guinea pigs [8][9][10] . Exposing neurons in the guinea pig small intestinal myenteric or submucosal plexus to BK in vitro evokes slow activation of depolarization of the membrane potential and enhanced excitability characterized by increased firing frequency during intraneuronal injection of depolarizing current pulses in both AH-and S-type neurons and the appearance of anodal break excitation at the offset of hyperpolarizing current pulses in AH neurons [8,9] . The results suggested that BK acts via B2R on myenteric and submucosal neurons to stimulate the formation of prostaglandins.…”

“…BK receptors belong to the family of G-protein-coupled receptors with seven transmembrane helices. BK and kallidin are ligands for the constitutively expressed B2R, whereas des-Arg 9 -BK (in rodents) and des-Arg 10 -kallidin (in human) are ligands for the inducible B1R [6,7] . Previously, we demonstrated that B2R is expressed on a majority of the ganglion cells in the myenteric and submucosal plexuses in the small intestine of guinea pigs [8][9][10] .…”

“…BK and kallidin are ligands for the constitutively expressed B2R, whereas des-Arg 9 -BK (in rodents) and des-Arg 10 -kallidin (in human) are ligands for the inducible B1R [6,7] . Previously, we demonstrated that B2R is expressed on a majority of the ganglion cells in the myenteric and submucosal plexuses in the small intestine of guinea pigs [8][9][10] . Exposing neurons in the guinea pig small intestinal myenteric or submucosal plexus to BK in vitro evokes slow activation of depolarization of the membrane potential and enhanced excitability characterized by increased firing frequency during intraneuronal injection of depolarizing current pulses in both AH-and S-type neurons and the appearance of anodal break excitation at the offset of hyperpolarizing current pulses in AH neurons [8,9] .…”