[³H]‐rauwolscine binding to α₂‐adrenoceptors in the mammalian kidney: apparent receptor heterogeneity between species

Abstract

(2.33-3.03 nM) except man where it was significantly higher (0.98 nM). Marked differences were seen in the density of binding sites, increasing in the order: man < dog < rabbit < rat < mouse. In all cases, Hill coefficients were not significantly different from unity. 4 [3H]-rauwolscine binds with low affinity (KD> 15 nM) to membranes prepared from guinea-pig kidney. The low affinity binding is not due to the absence of particular ions in the incubation medium or to receptor occupation by endogenous agonist. 5 The binding in all species was found to be stereoselective with respect to the isomers of noradrenaline. However, differences were seen in the characteristics of agonist interactions with the binding site both between isomers and between species.6 Marked differences in affinity of particular a-adrenoceptor antagonists were observed for a2-adrenoceptors labelled by [3H]-rauwolscine. These differences were most evident with the a,-adrenoceptor selective antagonist prazosin which displayed inhibition constants (K, values) of 33.2, 39.5, 261, 570 and 595 nM in rat, mouse, dog, man and rabbit, respectively. 7 Differences are apparent in the characteristics of a2-adrenoceptors labelled by [3H]-rauwolscine between species and it is suggested that the differences observed for a,-selective antagonists such as prazosin may be related to binding to additional sites in the vicinity of the a2-adrenoceptor.

Alpha 2 adrenergic agonists stimulate Na+-H+ antiport activity in the rabbit renal proximal tubule.

“…In addition, the KD of [3H]rauwolscine for alpha2 adrenergic binding sites (Fig. 8) was 5.4±1.4 nM, a value similar to that reported in membrane preparations from kidneys of rabbit, rat, dog, and mouse (9). Taken together, the functional studies and radioligand binding data complement one another and provide strong evidence that binding of alpha2 adrenergic agonists to their specific receptors resulted in enhanced Na+-H+ antiport activity.…”

“…With regard to rabbit kidney, Neylon and Summers (9) found specific alpha2 adrenergic binding sites in membrane fragments of renal cortex, with little evidence for alpha, adrenergic sites. Kusano and co-workers (23) using renal tubular fragments from different nephron segments demonstrated that alphaI adrenergic receptors were present on the proximal convoluted tubule (PCT) but not on the proximal straight tubule (PST).…”

α.‐Adrenoceptor modulation of the efferent function of capsaicin‐sensitive sensory neurones in guinea‐pig isolated atria

“…Again, the effect of phenylephrine was antagonized by prazosin, although less efficiently than by yohimbine. Thus, as well as in the cardiac adrenergic terminals of several animal species (Kobinger & Pichler, 1980;Docherty, 1983;Ledda & Mantelli, 1984 (Neylon & Summers, 1985;Harrison et al, 1991) including those of rat submandibular gland tissue slices and rat brain slices (Turner et al, 1984;Nasseri & Minneman 1987 . Only the effect of the imidazolines however is completely antagonized by M2-blockers, while noradrenaline shows a 'remaining effect' which is insensitive to a(X-, a2-or P-adrenoceptor blockers (Bond et al, 1986a;b).…”

Role of α2-adrenoceptors in enhancement of antinociceptive effect in diabetic mice

“…Crude synaptic membranes were prepared according to the method of Neylon and Summers (1985). Mice were decapitated 2 weeks after injection of streptozotocin.…”

“…The protein concentration was determined by the method of Lowry et al (1951). [ 3 H]-rauwolscine binding was determined using the method of Neylon and Summers (1985). About 300 µg protein of the membrane preparation was incubated for 60 min at 25°C with 0.5 to 20 nM concentrations of …”