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Brain Res ; 942(1-2): 11-22, 2002 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-12031848

RESUMO

The inhibitory effects of opioids on voltage-dependent calcium channels (VDCCs) were investigated in cultured porcine adrenal chromaffin cells using whole-cell patch clamp technique. The effects of the opioid on [Ca(2+)](i) increase and catecholamine secretion induced by high K(+) were also examined in single cells by fura-2 microfluorimetry and amperometry. A depolarizing pulse to 0 mV (test pulse) from a holding potential of -80 mV evoked an inward barium current (I(Ba)), which was reversibly inhibited by methionine-enkephalin. This inhibitory effect of methionine-enkephalin was abolished by naloxone. Selective agonists of opioid receptor subtypes (DAMGO: mu, DPDPE: delta, U50488: kappa) dose-dependently inhibited I(Ba). In inhibitory potency, the order was DAMGO>U50488>DPDPE. These agonists applied sequentially produced a reversible I(Ba) inhibition in the same cells. The inhibitory effect of DAMGO on I(Ba) almost disappeared in the presence of omega-conotoxin GVIA but not omega-agatoxin IVA plus nifedipine. Application of a conditioning prepulse to +100 mV prior to the test pulse partly retrieved the I(Ba) inhibition by DAMGO, suggesting the involvement of voltage-sensitive components in opioid-induced VDCC inhibition. Intracellular application of GDPbetaS or GTPgammaS as well as pretreatment with pertussis toxin significantly reduced the extent of I(Ba) inhibition induced by DAMGO. DAMGO reversibly inhibited the [Ca(2+)](i) increase and catecholamine release induced by high K(+). RT-PCR revealed the expression of mu-, delta- and kappa-opioid receptor mRNAs in cultured adrenal chromaffin cells. These results suggest that porcine adrenal chromaffin cells possess mu-, delta- and kappa-opioid receptors and activation of opioid receptors mainly inhibits N-type VDCCs via pertussis toxin-sensitive G-proteins.


Assuntos
Medula Suprarrenal/metabolismo , Canais de Cálcio/metabolismo , Catecolaminas/metabolismo , Células Cromafins/metabolismo , Entorpecentes/metabolismo , Inibição Neural/fisiologia , Receptores Opioides/metabolismo , (trans)-Isômero de 3,4-dicloro-N-metil-N-(2-(1-pirrolidinil)-ciclo-hexil)-benzenoacetamida/farmacologia , Medula Suprarrenal/efeitos dos fármacos , Animais , Bário/farmacologia , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio/efeitos dos fármacos , Canais de Cálcio Tipo N/efeitos dos fármacos , Canais de Cálcio Tipo N/metabolismo , Sinalização do Cálcio/efeitos dos fármacos , Sinalização do Cálcio/fisiologia , Células Cromafins/efeitos dos fármacos , Relação Dose-Resposta a Droga , Estimulação Elétrica , Ala(2)-MePhe(4)-Gly(5)-Encefalina/farmacologia , D-Penicilina (2,5)-Encefalina/farmacologia , Encefalina Metionina/metabolismo , Encefalina Metionina/farmacologia , Proteínas de Ligação ao GTP/efeitos dos fármacos , Proteínas de Ligação ao GTP/metabolismo , Guanosina 5'-O-(3-Tiotrifosfato)/farmacologia , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Entorpecentes/farmacologia , Inibição Neural/efeitos dos fármacos , Cloreto de Potássio/farmacologia , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/metabolismo , Receptores Opioides/efeitos dos fármacos , Receptores Opioides/genética , Suínos
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