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Somatostatin Receptor-mediated Signaling in Smooth Muscle

1996; Elsevier BV; Volume: 271; Issue: 38 Linguagem: Inglês

10.1074/jbc.271.38.23458

1083-351X

Karnam S. Murthy, David H. Coy, Gabriel M. Makhlouf,

PI3K/AKT/mTOR signaling in cancer

In COS-7 cells, all five cloned somatostatin receptors are coupled via inhibitory G proteins to activation of an unidentified phospholipase C-β (PLC-β) 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-β isozymes were used to identify the PLC-β isozyme and the G proteins coupled to it and to adenylyl cyclase.Somatostatin-14 bound with high affinity to intestinal SMC; stimulated -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 (∼80%) by pretreatment with antibodies to PLC-β3 but not other PLC-β isozymes, and by antibodies to Gβ but not Gα. Inhibition of cAMP formation was partially blocked by antibody to Gαi1 or Gαo and additively blocked by a combination of both antibodies. Somatostatin-stimulated [35S]GTPγS-Gα complexes in plasma membranes were bound selectively by Gαi1 and Gαo antibodies.We conclude that in smooth muscle sstr3 is coupled to Gi1 and Go; the α subunits of both G proteins mediate inhibition of adenylyl cyclase, while the βγ subunits mediate activation of PLC-β3. In COS-7 cells, all five cloned somatostatin receptors are coupled via inhibitory G proteins to activation of an unidentified phospholipase C-β (PLC-β) 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-β isozymes were used to identify the PLC-β isozyme and the G proteins coupled to it and to adenylyl cyclase. Somatostatin-14 bound with high affinity to intestinal SMC; stimulated -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 (∼80%) by pretreatment with antibodies to PLC-β3 but not other PLC-β isozymes, and by antibodies to Gβ but not Gα. Inhibition of cAMP formation was partially blocked by antibody to Gαi1 or Gαo and additively blocked by a combination of both antibodies. Somatostatin-stimulated [35S]GTPγS-Gα complexes in plasma membranes were bound selectively by Gαi1 and Gαo antibodies. We conclude that in smooth muscle sstr3 is coupled to Gi1 and Go; the α subunits of both G proteins mediate inhibition of adenylyl cyclase, while the βγ subunits mediate activation of PLC-β3.