Somatostatin receptor-mediated signaling in smooth muscle. Activation of phospholipase C-beta3 by Gbetagamma and inhibition of adenylyl cyclase by Galphai1 and Galphao.
In COS-7 cells, all five cloned somatostatin receptors are coupled via inhibitory G proteins to activation of an unidentified phospholipase C-beta (PLC-beta) isozyme and inhibition of adenylyl cyclase. In the present study, intestinal smooth muscle cells (SMC) that express only one receptor type, sstr3, and possess a full complement of G proteins and PLC-beta isozymes were used to identify the PLC-beta isozyme and the G proteins coupled to it and to adenylyl cyclase. Somatostatin-14 bound with high affinity to intestinal SMC; stimulated D-myo-inositol-1,4,5-trisphosphate (IP3) formation, Ca2+ release, and contraction; and inhibited forskolin-stimulated cAMP formation in a pertussis toxin-sensitive fashion. Somatostatin also stimulated phosphoinositide hydrolysis in plasma membranes. Only those somatostatin analogs that shared a high affinity for sstr3 receptors elicited muscle contraction. IP3 formation, Ca2+ release, and contraction in permeabilized SMC and phosphoinositide hydrolysis in plasma membranes were inhibited (approximately 80%) by pretreatment with antibodies to PLC-beta3 but not other PLC-beta isozymes, and by antibodies to Gbeta but not Galpha. Inhibition of cAMP formation was partially blocked by antibody to Galphai1 or Galphao and additively blocked by a combination of both antibodies. Somatostatin-stimulated [35S]GTPgammaS-Galpha complexes in plasma membranes were bound selectively by Galphai1 and Galphao antibodies. We conclude that in smooth muscle sstr3 is coupled to Gi1 and Go; the alpha subunits of both G proteins mediate inhibition of adenylyl cyclase, while the betagamma subunits mediate activation of PLC-beta3.
Murthy
K S
KS
Department of Physiology, Medical College of Virginia, Richmond, Virginia 23298-0711, USA.
Coy
D H
DH
Makhlouf
G M
GM
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002469:Cell Separation; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006168:Guinea Pigs; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007422:Intestines / Q000166:cytology; D007527:Isoenzymes / Q000276:immunology / Q000378:metabolism*; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin; D054799:Phospholipase C beta; D017481:Receptors, Somatostatin / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013004:Somatostatin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000276:immunology / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000906:Antibodies; D007527:Isoenzymes; D017481:Receptors, Somatostatin; D010566:Virulence Factors, Bordetella; D005576:Colforsin; D013004:Somatostatin; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D002118:Calcium