Surface interaction of [3
H]norepinephrine with cultured chick embryo myocardial cells
Cultured chick embryo cardiac myoblasts specifically bind [3H]nonrepinephrine. The binding is rapid and reversible. Bound [3H]nonrepinephrine, dissociated by 1 M HCl, can be rebound to fresh cells. β-Adrenergic catecholamines were most potent in displacing [3H]nonrepinephrine from the cellular bindign sites. The binding reaction did not show stereospecificity. α-Adrenergic amines were much less potent. Propranolol, but no phentolamine, competed for the sites. Approximately 2.5 · 106 specific binding sites are present per myocardial cell. The sites appear to be present predominantly at the cell surface in that nonrepinephrine linked to agarose beads competes for th sites. Similarly, the sites were degraded by either trypsin or trypsin bound to agarose. Two different binding constants, K = 2 · 106 and 1 · 105, were observed. Proteolytic enzymes decreased binding whereas certain hospholipases led to an increase in specific binding. Divalent cations at concentrations > 1 mM diminished binding as did chelating agents. © 1974.
Lefkowitz, RJ; O'Hara, D; Warshaw, JB
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