ISSN:
1432-136X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The binding properties of A1 adenosine receptors in brain membranes were compared in two congeneric marine teleost fishes which differ in their depths of distribution. Adenosine receptors were labeled using the A1 selective radioligand [3H]cyclohexyladenosine ([3H]CHA). The A1 receptor agonist [3H]CHA bound saturably, reversibly and with high affinity to brain membranes prepared fromSebastolobus altivelis andS. alascanus; however, the meanK d values differed significantly (Figs. 1–3, Table 1). Saturation data fit to a one site model indicated that the A1 receptor inS. alascanus exhibited a higher affinity (K d=1.49 nM) for [3H]CHA whereas A1 receptors inS. altivelis exhibited a significantly lower affinity (K d=3.1 nM). Moreover,S. altivelis, but notS. alascanus, parameter estimates for [3H]CHA binding to two sites of receptor were obtained (Fig. 3, Table 1). The mean dissociation constant values for the high and low affinity sites for [3H]CHA inS. altivelis were 0.43 nM and 16.3 nM, respectively. In equilibrium competition experiments the adenosine analogs R-phenylisopropyladenosine (R-PIA), N-ethylcarboxamidoadenosine (NECA) and S-phenylisopropyladenosine (S-PIA) all displayed higher affinities for A1 receptors inS. alascanus as compared toS. altivelis brain membranes (Table 2, Fig. 6). The specific binding of [3H]CHA was significantly increased by 0.1 and 1.0 mM MgCl2 in both fishes; however, the sensitivity (95–131% increase) ofS. altivelis to this effect was significantly greater than that ofS. alascanus (48–91% increase) (Fig. 5). The results of kinetic, equilibrium saturation and equilibrium competition experiments all suggest that A1 adenosine receptors ofS. altivelis andS. alascanus brain membranes differ with respect to their affinities for selected adenosine agonists.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00693353
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