Involvement of G-protein βγ subunits on the influence of inhibitory α2-autoreceptors on the angiotensin AT1-receptor modulation of noradrenaline release in the rat vas deferens.
The influence of alpha2-autoreceptors on the facilitation of [3H]-noradrenaline release mediated by angiotensin II was studied in prostatic portions of rat vas deferens preincubated with [3H]-noradrenaline. Angiotensin II enhanced tritium overflow evoked by trains of 100 pulses at 8 Hz, an effect that was attenuated by the AT1-receptor antagonist losartan (0.3-1 microM), at concentrations suggesting the involvement of the AT1B subtype. The effect of angiotensin II was also attenuated by inhibition of phospholipase C (PLC) and protein kinase C (PKC) indicating that prejunctional AT1-receptors are coupled to the PLC-PKC pathway. Angiotensin II (0.3-100 nM) enhanced tritium overflow more markedly, up to 64%, under conditions that favor alpha2-autoinhibition, observed when stimulation consisted of 100 pulses at 8 Hz, than under poor alpha2-autoinhibition conditions, only up to 14%, observed when alpha2-adrenoceptors were blocked with yohimbine (1 microM) or when stimulation consisted of 20 pulses at 50 Hz. Activation of PKC with 12-myristate 13-acetate (PMA, 0.1-3 microM) also enhanced tritium overflow more markedly under strong alpha2-autoinhibition conditions. Inhibition of Gi/o-proteins with pertussis toxin (8 microg/ml) or blockade of Gbetagamma subunits with the anti-betagamma peptide MPS-Phos (30 microM) attenuated the effects of angiotensin II and PMA. The results indicate that activation of AT1-receptors coupled to the PLC-PKC pathway enhances noradrenaline release, an effect that is markedly favoured by an ongoing activation of alpha2-autoreceptors. Interaction between alpha2-adrenoceptors and AT1-receptors seems to involve the betagamma subunits released from the Gi/o-proteins coupled to alpha2-adrenoceptors and protein kinase C activated by AT1-receptors.
Talaia
Carlos
C
Laboratory of Pharmacology, CEQOFFUP, Faculty of Pharmacy, University of Porto, Rua Aníbal Cunha, 164, 4050-047 Porto, Portugal.
Queiroz
Glória
G
Pinheiro
Helder
H
Moura
Daniel
D
Gonçalves
Jorge
J
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000804:Angiotensin II / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D017660:Autoreceptors / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D044387:GTP-Binding Protein beta Subunits / Q000037:antagonists & inhibitors / Q000378:metabolism*; D044388:GTP-Binding Protein gamma Subunits / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism*; D037342:Pertussis Toxin / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D044140:Receptor, Angiotensin, Type 1 / Q000187:drug effects* / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D017779:Sympathetic Fibers, Postganglionic / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014316:Tritium; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*
D000317:Adrenergic alpha-Antagonists; D017660:Autoreceptors; D004791:Enzyme Inhibitors; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D044140:Receptor, Angiotensin, Type 1; D018341:Receptors, Adrenergic, alpha-2; D014316:Tritium; D000804:Angiotensin II; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010738:Type C Phospholipases; D009638:Norepinephrine