Showing papers by "Robert J. Lefkowitz published in 1974"

(3H)-Propranolol binding sites in myocardial membranes: nonidentity with beta adrenergic receptors.

Abstract: [3H]Propranolol binds rapidly and reversibly to sites in membranes prepared from canine ventricular myocardium. Two orders of sites were identified. The higher-order sites have a value (equilibrum constant) of 4.57 x 104 M-1 and a binding capacity of 3.2 x 10-8 mole/ mg of protein. For the lower-order sites K = 4.32 x 102 M-1 and binding capacity is 8.4 x 10-7 mole/mg of protein. Nine adrenergic antagonist drugs were tested for their ability to block [3H]propranolol binding and block isoproterenol activation of adenylate cyclase in dog heart membranes. No clear correlation between the two functions was found. d - and l -Propranolol competed with equal effectiveness for the propranolol binding sites, but l -propranolol was 50 times more potent than the d isomer in blocking cyclase activation. The beta adrenergic blocking agent dichloroisoproterenol was a very weak inhibitor of [3H]-propranolol binding. Chlorpromazine and haloperidol inhibited both propranolol binding and cyclase activation. It is concluded that the [3H]propranolol binding sites studied here are unrelated to the myocardial beta adrenergic receptors and may be involved in mediating the more general membrane or local anesthetic effects of propranolol. Beta adrenergic receptor binding sites presumably represent too small a fraction of myocardial membrane sites capable of binding propranolol to be revealed by binding studies of this type. ACKNOWLEDGMENT The authors are indebted to Dr. Edgar Harber, Massachusetts General Hospital, in whose laboratory part of these studies were performed.

Temperature immutability of adenyl cyclase-coupled β adrenergic recptors

Abstract: OBSERVATIONS from several laboratories have suggested that the well established classification of adrenergic receptors into α and β subtypes is not immutable. Several groups have reported that in isolated perfused frog hearts, stimulation of cardiac rate and contractility by catecholamines has the properties of a classical β adrenergic response when experiments are performed at warm temperatures (25°–37° C) but of an α adrenergic response when experiments are performed at cold temperatures (5°–15° C)1–3. At warm temperatures, the order of potency of agonists in stimulating these preparations—isoproterenol>adrenaline>noradrenaline—is classical for a β adrenergic receptor. Similarly, effects of the catecholamines at warm temperatures are blocked by propranolol but not by the α adrenergic antagonist phentolamine. When the same experiments are performed at temperatures below 25° C, the order of potency of agonists is reversed to that characteristic of α adrenergic receptors. Also at lower temperatures α adrenergic antagonists such as phenoxybenzamine and phentolamine block the effects of adrenaline, whereas β adrenergic antagonists such as propranolol are ineffective. Gradations of response can be achieved by varying the temperature between 37° C and 10° C. Similar observations have been reported for the rat heart1. Also in a dog heart–lung bypass preparation the β receptors seem to become ineffective at 15° C, whereas α receptors retain their effectiveness4. On the basis of such observations, Kunos et al.3 proposed that α and β adrenergic receptors may represent allosteric configurations of the same receptor macromolecule which could be modulated by among other factors, temperature.

Selectivity in Beta-Adrenergic Responses Clinical Implications

Abstract: THE CONCEPT of drug receptors and of selectivity in drug action is of fundamental importance both to clinicians as they select agents for specific therapeutic problems and for researchers investigating the molecular basis of drug action. Receptors are those cellular structures with which drugs or hormones initially interact. They perform two crucial functions. First, they recognize or discriminate certain biologically active molecules, e.g., adrenergic receptors bind catecholamines, cholinergic receptors bind acetylcholine and related drugs. Second, they transmit a signal which alters certain cellular functions such as enzymes, e.g., adenylate cyclase and ion impermeability of membranes. Thus, receptors determine which drug or drugs will affect a given tissue response-such as cardiac contractility, or rate. The idea of a receptive mechanism for drugs was first clearly described by Langley about 70 years ago.' Adrenergic receptors were first discussed by Dale.2 Our current classification of adrenergic receptors into two basic types, a and /3, was originated by Ahlquist some 25 years ago.3 His

Affinity chromatography of adrenergic receptors and binding proteins.

Abstract: Publisher Summary Methodology has been developed for preparation and study of adrenergic binding proteins from membranes of several tissues. These binding proteins that may function as part of the adrenergic receptor complex can be solubilized and purified by affinity chromatography. The biological effects of catecholamines are initiated by their binding to specific adrenergic receptor binding sites. These receptors trigger subsequent events that lead to such diverse responses as smooth muscle contraction or relaxation, increased force of cardiac muscle contraction, increased rate of glycogenolysis, and increased rate of lipolysis. A number of actions of catecholamines are brought about by stimulation of the enzyme adenylate cyclase. The receptors that mediate catecholamine stimulation of this enzyme generally have the characteristics of so-called “β-adrenergic receptors.” As with other hormone receptors, these appear to be proteins localized in membranes of responsive tissues.