Endothelin receptor-mediated Ca2+ mobilization and contraction in bovine oviductal arteries: comparison with noradrenaline and potassium.
1. The effects of endothelin-1 (ET-1) were studied in bovine oviductal arteries and compared to those of noradrenaline (NA) and high K+ (K+). The influence of endothelium, the receptor subtypes involved, and the mechanisms of Ca2+ mobilization were assessed. 2. ET-1 (0.1-300 nM) induced concentration-dependent contractions with a potency of 10(3) and 10(2) times higher than NA (0.1 microM-0.1 mM) and K+ (9.5-119 mM), respectively. Removal of endothelium or NG-nitro-L-arginine (L-NOARG, 0.1 mM) pretreatment did not affect responses to either ET-1 or K+, whereas the NA response was significantly increased. Indomethacin (1 microM) had no effect on either of these agonists. 3. The rank order of potency for the ET isopeptides was: ET-1 = ET-2 > ET-3. The ETA receptor-selective agonist, sarafotoxin 6c (S6c), had no effect. The ETA receptor-selective antagonist, BQ-123, showed a competitive antagonism on the ET-1 response (pA2 value of 6.58 +/- 0.01), whereas contractions to ET-3 were completely abolished by BQ-123 at 0.1 microM. 4. Concentration-response curves to both ET-1 and NA were shifted to the right and their maximum response reduced to approximately 56% and 65% of controls, respectively, under 30 min of incubation in Ca(2+)-free solution, whereas responses to K+ were almost abolished by this treatment. Contractions to both NA (30 microM) and ET-1 (30 nM) were maximally inhibited after 10 min of extracellular Ca2+ deprivation. 5. Contractions to ET-1 were more potently inhibited by nickel (Ni2+, 0.3 mM), whereas nifedipine (1 microM) and cadmium (Cd2+, 0.1 mM) induced only a slight effect. In contrast, opposite effects were found for both NA and K+. 6. Treatment with ryanodine (100 microM) and caffeine (10 mM) in Ca(2+)-free solution reduced the tension measured 5 min after NA (30 microM) and ET-1 (30 nM) addition, but the sustained response (tension at 25 min) remained unaffected. 7. Calphostin C (1 microM), a specific protein kinase C (PKC) inhibitor, reduced the maximum contractile response to ET-1 by about 50% without significantly affecting its pD2 value. 8. These results suggest that ET-1 acts in bovine oviductal arteries by directly activating a homogenous population of ETA receptors in smooth muscle, without endothelial modulation. Several Ca2+ activation mechanisms seem to be involved in the contractile action of the peptide, including: (1) extracellular Ca2+ entrance through Ni(2+)-sensitive and L-type Ca2+ channels; (2) intracellular Ca2+ release from a ryanodine-sensitive Ca2+ store; and (3) sensitization of the contractile machinery to Ca2+ via PKC.
Labadía
A
A
Department of Physiology, Faculty of Veterinary Sciences, Complutense University, Madrid, Spain.
Costa
G
G
Jimenez
E
E
Triguero
D
D
García-Pascual
A
A
D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002417:Cattle; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology; D019333:Endothelin-2 / Q000494:pharmacology; D019334:Endothelin-3 / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000502:physiology; D005187:Fallopian Tubes / Q000098:blood supply*; D005260:Female; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009532:Nickel / Q000494:pharmacology; D009543:Nifedipine / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D017466:Receptors, Endothelin / Q000819:agonists / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012433:Ryanodine / Q000494:pharmacology; D014757:Viper Venoms / Q000494:pharmacology
D002120:Calcium Channel Agonists; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D019333:Endothelin-2; D019334:Endothelin-3; D010456:Peptides, Cyclic; D017466:Receptors, Endothelin; D014757:Viper Venoms; C057354:sarafotoxins s6; D002104:Cadmium; D012433:Ryanodine; D019335:Nitroarginine; D002110:Caffeine; D009532:Nickel; D009543:Nifedipine; D011188:Potassium; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium; D009638:Norepinephrine; D007213:Indomethacin