Figure 1. Correlations between R-R interval and total, M₂ and M₃ muscarinic receptor density in hearts from normal (N) and vagal hyperreactive (H) rabbits.

R-R intervals were measured in conscious rabbits challenged with PNE 500 µg kg⁻¹ following the procedure described in Material and Methods. Total, M₂ and M₃ muscarinic receptor densities in hearts (B_max; fmol mg⁻¹ protein) were determined from Scatchard analysis of the saturation data using [³H]NMS, [³H]AF-DX 384 and [³H]4-DAMP, respectively, as radioligands. Binding conditions were as described in Material and Methods. Each symbol represents one animal. (a) Total muscarinic receptors; n = 9 H (full symbols) and 6 N (open symbols). (b) M₂ muscarinic receptors; n = 10 H (full symbols) and 7 N (open symbols). (c) M₃ muscarinic receptors; n = 10 H (full symbols) and 6 N (open symbols).