Formation of the high‐affinity agonist state of the α1‐adrenergic receptor at cold temperatures does not require a G‐protein

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Abstract
Two methods were employed to uncouple hepatic α1‐adrenergic receptors from their associated G‐protein (termed Gp) in order to determine wether locking of the α1‐receptor in a high‐affinity agonist state at cold temperatures (2°C) represents formation of a ternary complex. Uncoupling is defined as the inability to observe the GppNHp‐sensitive, high‐affinity agonist state of the receptor in [3H]prazosin competition binding studies performed at 25°C. The first method for achieving uncoupling involved brief alkalinization and resulted in greater 95% loss of several G‐proteins. The second method involved proteolytic cleavage of either part or all of the α1‐receptor coupling domain from the binding domain. Following either treatment, receptors were converted to the high‐affinity agonist state at 2°C. Thus, while formation of the high‐affinity state of the receptor at higher temperatures may require Gp, formation of this state at 2°C does not require Gp or even the entire α1‐adregenic receptor.

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