Adenosine Receptor from Rat Brain Membranes

A1 adenosine receptors from rat brain membranes were solubilized with the zwitterionic detergent 3-[3-( cholamidopropyl)dimeth ylammonio ]-1-propanesulfonate. The solubilized receptors retained all the characteristics of membrane-bound A1 adenosine receptors. A high and a low agonist affinity state for the radiolabelled agonist (R)-N'-eHJphenylisopropyladenosine((JH]PJA) with Kn values of 0.3 and 12 nM, respectively, were detected. High-affinity agonist binding was regulated by guanine nucleotides. In addition agonist binding was still modulated by divalent cations. The solubilized A1 adenosine receptors could be Iabelied not only with the Adenosine modulates a great variety of physiological functions through membrane-bound receptors coupled to the adenylate cyclase system. Two subtypes of adenosine receptors have been characterized mediating either inhibition (A 1 or R) or Stimulation (A1 or Ra) of adenylate cyclase (van Calker et al., 1978; Londos et al., 1980). A 1 adenosine receptors have been investigated in binding studies with radiolabelled agonists and antagonists in the CNS (Bruns et al., 1980; Schwabe and Trost, 1980) as well as in peripheral tissues (Trost and Schwabe, 1981; Lohse et al., 1985). Agonist affinity for A 1 adenosine receptors is regu1ated by divalent cations (Goodman et al., 1982; Ukena et al., 1984) and guanine nucleotides (Goodman et al., 1982; Lohsc ct al., 1984b; Ukena et al., 1984), suggesting that a guanine nucleotide binding regulatory protein (N) is involved in the coupling to adenylate cyclase (Rodbe11, 1980). Elucidation of the molecular mechanism involved in this coupling and biochemical characterization of the structural components will require solubilization of the adenosine