Allosteric Modulation of Renal α₂-Adrenoceptor Binding by Sodium in Inbred Dahl Rats

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We investigated the reported differences in the modulating effect of sodium on renal α₂-adrenoceptor binding between inbred Dahl Salt-Sensitive (S/JR) and Salt-Resistant (R/JR) Rats. Saturation binding of [³H]rauwolscine to renal α₂-adrenoceptors and its displacement by epinephrine were performed in the absence and presence of NaCl, GppNHp, or MgCl₂ in S/JR and R/JR rats. We omitted sucrose in our buffers which preserves endogenous catecholamines in renal membranes. MgCl₂ but not NaCl or GppNHp decreased the apparent density and affinity of renal α₂-adrenoceptors for [³H]rauwolscine in both strains. NaCl and GppNHp reduced and MgCl₂ increased the affinity of renal α₂-adrenoceptors for epinephrine in both strains. There were no differences in the modulating effects of sodium on renal α₂-adrenoceptor binding between the two strains except for the higher receptor density in S/JR than in R/JR rats. These data suggest that the difference in renal α₂-adrenoceptors between S/JR and R/JR is not due to alterations which affect receptor protein structure or interaction with G proteins. Thus, future investigations should be directed at the regulation of the receptor gene expression. (Hypertens Res 1994; 17: 179-185)