title: Contribution of different phospholipases and arachidonic acid metabolites in the response of gallbladder smooth muscle to cholecystokinin.
abstract: Guinea pig gallbladder muscle strips were used to investigate the contribution of different sources of diacylglicerol (DAG) in the cholecystokinin (CCK)-induced contraction. The involvement of arachidonic acid (AA) in this response was also investigated. Three distinct pathways for DAG production were investigated with specific phospholipase (PL) inhibitors. U-73122 (10 microM) was used for inhibition of phosphoinositide-specific-PLC (PI-PLC), D-609 (100 microM) for phosphatidylcholine specific-PLC (PC-PLC), and propranolol (100 microM) for phospholipase D (PLD). Separate or combined inhibition of each of these enzymes showed that the CCK-induced output of DAG involves the parallel activation of each of these phospholipases. Thus, after inhibition of a PL subtype, the remaining subtypes were able to functionally compensate in mediating CCK-induced contraction. Inhibition of AA production via DAG-lipase or phospholipase A(2) (PLA(2)) was accomplished using RHC-80267 (40 microM), mepacrine (100 microM) and 4-BPB (100 microM). These inhibitors diminished contractile response, indicating that AA is an important modulator of CCK-induced contraction. Indomethacin (10 microM) and nordihydroguaiaretic acid (NDGA, 100 microM), which inhibit subsequent steps in AA metabolism through the cyclooxygenase and 5-lipooxygenase pathways, also inhibited contractions. Taken together, these results show that CCK redundantly activates PC-PLC, PI-PLC and PLD, to produce DAG, which in turn stimulates PKC and provides a substrate for the generation of AA. sPLA(2) is also a source of AA, whose metabolites are, in part, responsible for determining the magnitude of the CCK-evoked contraction.
authors.affiliation: Department of Physiology, University of Extremadura, 10071 Cáceres, Spain.
authors.forename: Soledad
authors.initials: S
authors.lastname: Alcón
authors.forename: Sara
authors.initials: S
authors.lastname: Morales
authors.forename: Pedro J
authors.initials: PJ
authors.lastname: Camello
authors.forename: María J
authors.initials: MJ
authors.lastname: Pozo
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism* / Q000502:physiology; D002766:Cholecystokinin / Q000494:pharmacology*; D004075:Diglycerides / Q000378:metabolism; D005704:Gallbladder / Q000166:cytology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D010740:Phospholipases / Q000378:metabolism*
chemical_list: D004075:Diglycerides; D016718:Arachidonic Acid; D002766:Cholecystokinin; D010740:Phospholipases