Endothelin(A) receptor subtype mediates endothelin-induced contractility in left ventricular cardiomyocytes isolated from rabbit myocardium.
Endothelin (ET)-1 is a potent positive inotropic agent, the effects of which are mediated by increases in cytosolic Ca(2+) in the myocardium. The object of this study was to examine 1) the influence of ET(A) and ET(B) receptor subtypes, and 2) the role of the phospholipase C (PLC) pathway in mediating ET-1-induced contraction. Left ventricular cardiomyocytes were isolated from the hearts of New Zealand White rabbits (2-2.5 kg) by the use of Langendorff perfusion with collagenase. Cardiomyocyte function was examined during unloaded, electrically stimulated (0.5 Hz) contractions with a video-edge detection system. ET-1 increased cell shortening with greater potency than ET-3: mean EC(50) values were 1.1 x 10(-11) and 2.6 x 10(-10) M, respectively. With the same order of potency, ET-1 and ET-3 increased (P <.05) velocity of cell shortening. The ET(A) receptor-selective antagonist ABT-627 shifted the ET-1-induced cell shortening response curve to the right with a pA(2) value of 10.3. The ET(B) receptor-selective antagonist A-192621 (10(-8)-10(-7) M) did not alter the concentration-response of ET-1. Moreover, the ET(B) receptor-selective agonist sarafotoxin 6c did not have any effect on cell shortening over the concentration range of 10(-11) to 10(-7) M. ET-1 in the presence of the PLC inhibitor U-73122 did not alter the contractile amplitude. However, ET-1 in the presence of the protein kinase C inhibitor bisindolylmalemide increased cell shortening. These findings indicate that 1) the ET(A) receptor subtype, and not the ET(B) receptor subtype, mediates the positive inotropic effect of ET-1, and 2) the response of ET-1 is mediated by a PLC pathway, but not through protein kinase C, in ventricular cardiomyocytes isolated from rabbit myocardium.
Kelso
E J
EJ
Cardiovascular Pharmacology Group, Centre for Cardiovascular Research, School of Medicine, The Queen's University of Belfast, Northern Ireland, United Kingdom. e.kelso@qub.ac.uk
McDermott
B J
BJ
Silke
B
B
Spiers
J P
JP
D000818:Animals; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology*; D019334:Endothelin-3 / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000166:cytology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011817:Rabbits; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000819:agonists / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000502:physiology; D016276:Ventricular Function; D014757:Viper Venoms / Q000494:pharmacology
D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D019334:Endothelin-3; D004791:Enzyme Inhibitors; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; D014757:Viper Venoms; C057354:sarafotoxins s6; D011493:Protein Kinase C; D010738:Type C Phospholipases