Pharmacological similarities between native brain and heterologously expressed α4β2 nicotinic receptors

1. We studied the pharmacological properties of native rat brain and heterologously expressed rat α4β2 nicotinic receptors immunoprecipitated onto a fixed substrate with the anti-α4 antibody mAb 299. 2. Immunodepletion with the anti-β2 antibody mAb 270 showed that 89% of the mAb-299-precipitated rat brain receptors contained β2. 3. The association and dissociation rate constants for 30 pM ± [³H]-epibatidine binding to α4β2 receptors expressed in oocytes were 0.02 ± 0.01 and 0.03 ± 0.01 min^-1 (± standard error, degrees of freedom = 7-8) at 20-23°C. 4. The Hill coefficients for ± [³H] epibatidine binding to the native brain, α4β2 receptors expressed in oocytes, and α4β2 receptors expressed in CV-1 cells (using recombinant adenovirus) were 0.69-0.70 suggesting a heterogeneous receptor population. Fits of the ± [³H]-epibatidine concentration-binding data to a two-site model gave K(D)s of 8-30 and 560-1.200 pM. The high-affinity sites comprised 73-74% of the native brain and oocyte α4β2 receptor population, 85% of the CV-1 α4β2 receptor population. 5. The expression of rat α4β2 receptors in CV-1 cells using vaccinia viral infection-transfection resulted in a more homogeneous receptor population (Hill coefficient of 1.0 ± 0.2). Fits of the ± [³H]-epibatidine binding data to a single-site model gave a K(D) of 40 ± 3 pM. 6. DHβE (IC₅₀ = 260-470 nM) and the novel nicotine analogue NDNI (IC₅₀ = 7-10 μM) inhibited 30 pM ± [³H]-epibatidine binding to the native brain and heterologously expressed α4β2 receptors equally well. 7. The results show that α4β2-containing nicotinic receptors in the rat brain and heterologously expressed rat α4β2 receptors have similar affinities for ± [3H]-epibatidine, DHβE, and NDNI.