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Recent interest has focused on antibodies that can discriminate between different receptor conformations. Here we have characterised the effect of a monoclonal antibody (mAb3), raised against a purified thermo-stabilised turkey β 1 -adrenoceptor (β 1 AR-m23 StaR), on β 1 -ARs expressed in CHO-K1 or HEK 293 cells. Immunohistochemical and radioligand-binding studies demonstrated that mAb3 was able to bind to ECL2 of the tβ 1 -AR, but not its human homologue. Specific binding of mAb3 to tβ 1 -AR was inhibited by a peptide based on the turkey, but not the human, ECL2 sequence. Studies with [ 3 H]-CGP 12177 demonstrated that mAb3 prevented the binding of orthosteric ligands to a subset ( circa 40%) of turkey β 1 -receptors expressed in both CHO K1 and HEK 293 cells. MAb3 significantly reduced the maximum specific binding capacity of [ 3 H]-CGP-12177 without influencing its binding affinity. Substitution of ECL2 of tβ 1 -AR with its human equivalent, or mutation of residues D186S, P187D, Q188E prevented the inhibition of [ 3 H]-CGP 12177 binding by mAb3. MAb3 also elicited a negative allosteric effect on agonist-stimulated cAMP responses. The identity of the subset of turkey β 1 -adrenoceptors influenced by mAb3 remains to be established but mAb3 should become an important tool to investigate the nature of β 1 -AR conformational states and oligomeric complexes. [ABSTRACT FROM AUTHOR]

Why are a few drugs with properties beyond the rule of 5 (bRo5) absorbed across the intestinal mucosa while most other bRo5 compounds are not? Are such exceptional bRo5 compounds exclusively taken up by carrier-mediated transport or are they able to permeate the lipid bilayer (passive lipoidal diffusion)? Our experimental data with liposomes indicate that tetracycline, which violates one rule of the Ro5, and rifampicin, violating three of the rules, significantly permeate a phospholipid bilayer with kinetics similar to labetalol and metoprolol, respectively. Published data from experimental work and molecular dynamics simulations suggest that the formation of intramolecular H-bonds and the possibility to adopt an elongated shape besides the presence of a significant fraction of net neutral species facilitate lipid bilayer permeation. As an alternative to lipid bilayer permeation, carrier proteins can be targeted to improve absorption, with the potential drawbacks of drug–drug interactions and non-linear pharmacokinetics. [ABSTRACT FROM AUTHOR]