title: Differential expression of multidrug resistance protein 5 and phosphodiesterase 5 and regulation of cGMP levels in phasic and tonic smooth muscle.
abstract: Previous studies have identified differences in the expression of proteins that regulate myosin light chain phosphorylation and contraction in tonic and phasic smooth muscle. cGMP plays a critical role in smooth muscle relaxation and is important for optimal function of phasic and tonic smooth muscle. The intracellular cGMP levels are regulated by its hydrolysis via phosphodiesterase 5 (PDE5) and efflux via novel multidrug resistance protein 5 (MRP5). In the present study we tested the hypothesis that the differences in the phasic and tonic behavior of smooth muscles may be related to differences in mechanisms that terminate cGMP signaling. Expression of PDE5 and MRP5 was significantly (more than 2-fold) higher in fundus compared with antrum. The NO donor S-nitrosoglutathione (GSNO) caused an increase in PDE5 activity and intra- and extracellular cGMP levels in both fundus and antrum. Stimulation of PDE5 activity and increase in extracellular cGMP were significantly higher in fundus, whereas increase in intracellular cGMP was significantly higher in antrum. GSNO-induced increase in extracellular cGMP was blocked in dispersed cells by the cyclic nucleotide export blocker probenecid and in cultured muscle cells by depletion of ATP or suppression of MRP5 by siRNA, providing evidence that cGMP efflux was mediated by ATP-dependent export via MRP5. Consistent with the higher expression and activity levels of PDE5 and MRP5, GSNO-induced PKG activity and muscle relaxation were significantly lower in muscle cells from fundus compared with antrum. Thus higher expression of PDE5 and MRP5 in muscle cells from fundus correlates with tonic phenotype of muscle.
authors.affiliation: Dept. of Physiology and Biophysics, Virginia Commonwealth Univ., Richmond, VA 23298-0711. skarnam@vcu.edu.
authors.forename: Othman
authors.initials: O
authors.lastname: Al-Shboul
authors.forename: Sunila
authors.initials: S
authors.lastname: Mahavadi
authors.forename: Wimolpak
authors.initials: W
authors.lastname: Sriwai
authors.forename: John R
authors.initials: JR
authors.lastname: Grider
authors.forename: Karnam S
authors.initials: KS
authors.lastname: Murthy
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005748:Gastric Fundus / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006868:Hydrolysis; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology*; D009569:Nitric Oxide / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010641:Phenotype; D011706:Pyloric Antrum / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D015290:Second Messenger Systems; D013997:Time Factors; D014162:Transfection
chemical_list: D000255:Adenosine Triphosphate; D006152:Cyclic GMP; D017869:Cyclic GMP-Dependent Protein Kinases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009569:Nitric Oxide; D020030:Nitric Oxide Donors; D012333:RNA, Messenger
keywords: MRP5; cyclic nucleotides; phasic muscle; tonic muscle