Differential effects of endothelin-1 on basal and isoprenaline-enhanced Ca2+ current in guinea-pig ventricular myocytes.
1. We examined the effect of endothelin-1 (ET-1) on basal and isoprenaline-enhanced L-type Ca2+ current (ICa,L) in guinea-pig ventricular myocytes under nystatin-perforated patch configuration. 2. ET-1 at concentrations of 1, 5 and 10 nM had little effect on basal ICa,L. However, ICa,L enhanced by isoprenaline (500 nM) was significantly attenuated by 5 nM ET-1 by more than 50%. This effect was reversed upon washout. ICa,L enhanced by forskolin was also decreased by ET-1. 3. The inhibitory effect of ET-1 against isoprenaline was completely blocked by the ETA receptor antagonist BQ-123 (1 microM). In myocytes incubated with pertussis toxin (PTX, 2 micrograms ml-1) for 5 h, ET-1 did not inhibit isoprenaline-enhanced ICa,L. 4. Although ET-1 has been shown to activate specific protein kinase C (PKC) isoforms, a significant inhibitory effect of ET-1 was maintained in the presence of the PKC inhibitor bisindolylmaleimide (20 nM). The nitric oxide (NO) donor SIN-1 (10 microM) attenuated but failed to prevent the ET-1 effect. 5. In summary, our results demonstrate that ET-1 is devoid of any significant effects on basal ICa,L. However, it exerts a potent inhibitory effect against isoprenaline-enhanced ICa,L. This effect is mediated through ETA receptors coupled to PTX-sensitive G-proteins and occurs in the presence of PKC inhibition and NO generation.
Thomas
G P
GP
Department of Pharmacology and Toxicology, University of Western Ontario, London, Canada.
Sims
S M
SM
Karmazyn
M
M
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D019332:Endothelin-1 / Q000494:pharmacology*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006352:Heart Ventricles; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008301:Maleimides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology; D009761:Nystatin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D019332:Endothelin-1; D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D008301:Maleimides; D010566:Virulence Factors, Bordetella; D009761:Nystatin; D009569:Nitric Oxide; C002385:linsidomine; D008981:Molsidomine; D037342:Pertussis Toxin; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D007545:Isoproterenol; C088060:bisindolylmaleimide