TY - JOUR
T1 - The quasi-irreversible nature of endothelin binding and G protein- linked signaling in cardiac myocytes
AU - Hilal-Dandan, Randa
AU - Villegas, Sonia
AU - Gonzalez, Annette
AU - Brunton, Laurence L.
PY - 1997
Y1 - 1997
N2 - In experiments on neonatal and adult rat ventricular myocytes, endothelin (ET) binding and the effects of ET on transmembrane signaling are quasi-irreversible. The ET(A) receptor antagonist BQ123 competes for binding and biochemical effects if added simultaneously with ET; when added after ET, the antagonist prevents neither binding nor activation of the G1 and G(q) pathways. At 4°C, at which internalization of the ligand should be minimized, the interaction of [125]ET is still irreversible. After binding of radio-labeled ligand at either 4°C or 37°C, only 50% of ligand is removed by acid washing. Permeabilization of the cells with Triton X-100 fails to release irreversibly bound ligand. Binding experiments in cell membranes mimic this irreversible binding. At 37°C, the addition of mercaptoethanol or dithiothreitol inhibits concurrent ET binding but does not cause the dissociation of previously bound ligand or the reversal of previously activated signaling. We conclude that ET binds irreversibly to myocytes, that this irreversibility is reflected in the biochemical responses of the cells to ET and that the irreversibility is more complex than the formation of S-S bonds between surface receptors and ET or internalization of bound ET. We interpret these findings and others in the literature in light of a testable model of ET(A) receptor/G protein/effector interaction in which quasi-irreversible binding of ET to the ET(A) receptor occurs before the interaction of the ligand/receptor complex with G protein and in which irreversible binding contributes to the prolonged effects of ET and is a prelude to refractoriness and to the slow regeneration of free ET(A) receptor.
AB - In experiments on neonatal and adult rat ventricular myocytes, endothelin (ET) binding and the effects of ET on transmembrane signaling are quasi-irreversible. The ET(A) receptor antagonist BQ123 competes for binding and biochemical effects if added simultaneously with ET; when added after ET, the antagonist prevents neither binding nor activation of the G1 and G(q) pathways. At 4°C, at which internalization of the ligand should be minimized, the interaction of [125]ET is still irreversible. After binding of radio-labeled ligand at either 4°C or 37°C, only 50% of ligand is removed by acid washing. Permeabilization of the cells with Triton X-100 fails to release irreversibly bound ligand. Binding experiments in cell membranes mimic this irreversible binding. At 37°C, the addition of mercaptoethanol or dithiothreitol inhibits concurrent ET binding but does not cause the dissociation of previously bound ligand or the reversal of previously activated signaling. We conclude that ET binds irreversibly to myocytes, that this irreversibility is reflected in the biochemical responses of the cells to ET and that the irreversibility is more complex than the formation of S-S bonds between surface receptors and ET or internalization of bound ET. We interpret these findings and others in the literature in light of a testable model of ET(A) receptor/G protein/effector interaction in which quasi-irreversible binding of ET to the ET(A) receptor occurs before the interaction of the ligand/receptor complex with G protein and in which irreversible binding contributes to the prolonged effects of ET and is a prelude to refractoriness and to the slow regeneration of free ET(A) receptor.
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U2 - 10.1016/s0022-3565(24)36579-6
DO - 10.1016/s0022-3565(24)36579-6
M3 - Article
C2 - 9103506
AN - SCOPUS:0030953752
SN - 0022-3565
VL - 281
SP - 267
EP - 273
JO - Journal of Pharmacology and Experimental Therapeutics
JF - Journal of Pharmacology and Experimental Therapeutics
IS - 1
ER -