Phorbol ester and staurosporine modulation of antagonist and agonist binding to alpha-2 adrenergic receptors: differential influence on Na+ versus guanylylnucleotide regulation.
The modulatory influence of the protein kinase C (PKC) activator phorbol dibutyrate (pDBu) and the PKC inhibitor staurosporine on the binding of the antagonist rauwolscine and the agonist (-)-epinephrine to alpha-2 adrenergic receptors was studied in plasma membranes from bovine aorta. In control membranes [3H]rauwolscine binding exhibited high (KDH = 110 pM) and low (KDL = 2.4 nM) affinity components. The addition of 0.1 mM 5'-guanylylimidodiphosphate [Gpp(NH)p] reduced binding to a single component (KD = 1.3 nM) and the addition of 140 mM NaCl increased the proportion of high affinity sites from 7 to 15%, whereas the combination of both Gpp(NH)p and NaCl did not differ from values for NaCl alone. PDBu pretreatment had little effect on [3H]rauwolscine binding with the exception of a small increase in KD in the presence of Gpp(NH)p. Staurosporine pretreatment, however, eliminated the high-affinity component in the absence of Gpp(NH)p or NaCl and rendered Gpp(NH)p ineffective. NaCl was able to restore two components of [3H]rauwolscine binding to the same extent as in untreated membranes. Epinephrine displaced [3H]rauwolscine in a biphasic manner (KDH = 93 nM, KDL = 3.5 microM; %RH = 42). In untreated membranes Gpp(NH)p reduced epinephrine affinity, but did not alter the %RH. NaCl alone increased KDL and caused a partial decrease in %RH, whereas the combination of Gpp(NH)p and NaCl was required to produce a single, low-affinity state (KD = 11.9 microM). PDBu pretreatment reduced epinephrine affinity and blocked the effectiveness of Gpp(NH)p, but the action of NaCl was more pronounced than in untreated membranes.(ABSTRACT TRUNCATED AT 250 WORDS)
Jagadeesh
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Department of Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts.
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D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D002417:Cattle; D004837:Epinephrine / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology*; D066298:In Vitro Techniques; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000502:physiology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects* / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology*; D019311:Staurosporine; D015016:Yohimbine / Q000378:metabolism
D000470:Alkaloids; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D006165:Guanylyl Imidodiphosphate; D015240:Phorbol 12,13-Dibutyrate; D012964:Sodium; D011493:Protein Kinase C; D019311:Staurosporine; D004837:Epinephrine