Abstract
Endothelin (ET)-1 is a potent positive inotropic agent, the effects of which are mediated by increases in cytosolic Ca2+ in the myocardium. The object of this study was to examine 1) the influence of ETA and ETB 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 EC50 values were 1.1 × 10−11 and 2.6 × 10−10 M, respectively. With the same order of potency, ET-1 and ET-3 increased (P < .05) velocity of cell shortening. The ETA receptor-selective antagonist ABT-627 shifted the ET-1-induced cell shortening response curve to the right with a pA2 value of 10.3. The ETB receptor-selective antagonist A-192621 (10−8-10−7 M) did not alter the concentration-response of ET-1. Moreover, the ETBreceptor-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 ETA receptor subtype, and not the ETB 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.
Footnotes
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Send reprint requests to: Dr. Elizabeth J. Kelso, Department of Therapeutics and Pharmacology, The Queen's University of Belfast, Whitla Medical Building, 97 Lisburn Rd., Belfast BT9 7BL, Northern Ireland. E-mail: e.kelso{at}qub.ac.uk
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↵1 This study was supported by Wellcome Trust project Grant M/95/3141.
- Abbreviations:
- ET
- endothelin
- ETA
- endothelin receptor subtype A
- ETB
- endothelin receptor subtype B
- BQ-123
- cyclo[d-Trp-d-Asp-Pro-d-Val-Leu-]
- Sfx
- sarafotoxin 6c
- PLC
- phospholipase C
- ABT-627
- 2-(4-methoxyphenyl)-4-(1,3-benzodioxol-5-yl)-1-(N,N-di(n-butyl)amino carbonyl methyl)-pyrrolidine-3-carboxylic acid
- A-192621
- 2-(4-propoxyphenyl)-4-(1,3-benzodioxol-5-yl)-1-(2,5-ethylphenyl)amino carbonyl methyl)-pyrrolidine-3-carboxylic acid
- BIM
- bisindolylmalemide I
- U-73122
- 1-[6-[[(17β)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione
- PKC
- protein kinase C
- SR
- sarcoplasmic reticulum
- Received February 25, 2000.
- Accepted May 8, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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