Inhibitory effects of opioids on voltage-dependent Ca(2+) channels and catecholamine secretion in cultured porcine adrenal chromaffin cells.
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.
Kitamura
Go
G
Laboratory of Pharmacology, Department of Biomedical Science, Hokkaido University, Sapporo 0600818, Japan.
Ohta
Toshio
T
Kai
Takahiko
T
Kon
Yasuhiro
Y
Ito
Shigeo
S
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / Q000494:pharmacology; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism*; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000378:metabolism / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009294:Narcotics / Q000378:metabolism* / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011957:Receptors, Opioid / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013552:Swine
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020864:Calcium Channels, N-Type; D002395:Catecholamines; D009294:Narcotics; D012333:RNA, Messenger; D011957:Receptors, Opioid; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004744:Enkephalin, Methionine; D011189:Potassium Chloride; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D020881:Enkephalin, D-Penicillamine (2,5)-; D019204:GTP-Binding Proteins