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Vol. 294, Issue 3, 1047-1052, September 2000
Cardiovascular Pharmacology Group, Centre for Cardiovascular
Research, School of Medicine, The Queen's University of Belfast,
Northern Ireland, United Kingdom
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 × 1010 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 (108-107 M) did not
alter the concentration-response of ET-1. Moreover, the ETB
receptor-selective agonist sarafotoxin 6c did not have any
effect on cell shortening over the concentration range of 1011 to 107 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.
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