Signal transduction pathways mediating CCK-induced gallbladder muscle contraction

Abstract

The signal transduction that mediates CCK-induced contraction of gallbladder muscle was investigated in the cat. Contraction was measured by scanning micrometry in single muscle cells isolated enzymatically with collagenase. Production ofd- myo-inositol 1,4,5-trisphosphate (IP3) and sn-1,2-diacylglycerol (DAG) was quantitated using HPLC and TLC, respectively. Protein kinase C (PKC) activity was determined by measuring the phosphorylation of a specific substrate peptide from myelin basic protein, Ac-MBP-(4—14). CCK-induced contraction was blocked by incubation in strontium medium, pertussis toxin (PTx), and antibodies against Giα3or βγ-subunits but was not blocked by Ca2+-free medium or by antibodies against Gq/11α, Giα1–2, or Goα. The contraction induced by CCK was inhibited by the phospholipase C (PLC) inhibitor U-73122, anti-PLC-β3 antibody, and the IP3 receptor antagonist heparin but was not inhibited by the the phospholipase D inhibitor propranolol or antibodies against PLC-β1 or PLC-β2. Western blot analysis of gallbladder muscle revealed the presence of PLC-β2 and PLC-β3 but not PLC-β1. CCK caused a 94% increase in IP3 generation and an 86% increase in DAG generation. A low dose of CCK caused PKC translocation, and CCK-induced contraction was blocked by the PKC inhibitor H-7. A high dose of CCK, however, caused no PKC translocation, and its contraction was blocked by the calmodulin antagonist CGS9343B. In conclusion, CCK contracts cat gallbladder muscle by stimulating PTx-sensitive Gi 3 protein coupled with PLC-β3, producing IP3 and DAG. Low doses activate PKC, whereas high doses activate calmodulin.

Acidosis Inhibits Gallbladder Contraction Mediated by Protein Kinase C Activation

“…This tendency was similar to that of the degree of inhibition by acidosis of contractile responses to histamine and PGE2. Therefore, a protein kinase C-mediated pathway is involved in agonist-induced contraction, which agrees with a recent report showing that cholecystokinininduced gallbladder contraction is mediated by protein kinase C activation (11).…”

The Signal Transduction of Endothelin-1-Induced Circular Smooth Muscle Cell Contraction in Cat Esophagus

“…However, it has also been reported that ET-1 can activate G i/o proteins (Kasuya et al, 1992;Kimura et al, 1999). It has been suggested that agonist-induced contraction caused the production of IP 3 via a PTX-sensitive G protein-coupled PLC, and this signaling mechanism might be involved in the generation of contractile responses (Yu et al, 1998;An et al, 1999). Chan et al (2000) reported that enhancement of G q -dependent signals by G i -coupled receptors required activated PLC-␤ and was mediated via the ␤␥-dimer released from the G i .…”

Targeted disruption of the murine cholecystokinin-1 receptor promotes intestinal cholesterol absorption and susceptibility to cholesterol cholelithiasis

“…CCK administration in cholesterol gallstone patients is diminished compared with the response of normal subjects to the same treatment (48), suggesting that some gallstone patients might have impaired gallbladder CCK-1R function as well as reduced CCK-1R number and/or CCK-binding capacity to CCK-1Rs (49,50). Because there is impaired smooth muscle contractility in cell isolates from human gallbladders and from animal models with cholesterol gallstones, Behar and colleagues (51)(52)(53) have proposed that the gallbladder contractile mechanisms involve CCK-1R-mediated activation of phospholipase C, leading to signal-transduction decoupling when the sarcolemmas of the smooth muscle cells of the gallbladder are highly enriched in cholesterol. This may be attributed to a cholesterol-dependent decrease in the number of or dysfunction in CCK-1Rs of gallbladder smooth muscle (52), leading to impaired contractility.…”