Muscarinic receptors after syngeneic unilateral lung transplantation

We have characterized the muscarinic cholinergic receptor population by binding assay in left and right lung membranes from syngeneic Lewis rats one month after unilateral left lung transplantation and from controls. The density of muscarinic receptors measured by [3H](-)QNB binding was similar in left and right lung membranes one month after unilateral left lung transplantation (Bmax = 28.2 +/- 2.2 and 29.0 +/- 1.4 fmol/mg protein, respectively) and was similar between transplanted and control rats. Binding affinity also was similar on both sides (Kd = 28.5 +/- 9.5 and 32.3 +/- 2.7 pM, respectively). Binding parameters (Ki) of four selective muscarinic antagonists determined from competitive binding experiments of 0.5 nM [3H](-)QNB showed an order of potency: atropine > 4-DAMP > AF-DX 116 BS > pirenzepine both in transplanted and in control lungs. There was no significant difference in Ki values between left transplanted and right non transplanted lungs (1.8 +/- 0.1 and 1.9 +/- 0.1 nM; 4.3 +/- 0.5 and 3.5 +/- 0.5 nM; 80.9 +/- 13.8 and 78.9 +/- 18.8 nM; 480.4 +/- 40.9 and 481.7 +/- 78.2 nM, respectively for atropine, 4-DAMP, AF-DX 116 BS and pirenzepine). Values were also similar between transplanted and control lungs. These observations suggest a similar population of muscarinic receptors in the transplanted and the non transplanted lung in the Lewis rat. This result is in accordance with the similar physiological effect of exogenous acetylcholine that we previously observed in transplanted and non transplanted bronchi.