Expression of muscarinic acetylcholine receptors in turkey cardiac chambers

The aim of the present study was to characterize the specific binding sites for [N-methyl-3H]-scopolamine ([3H]NMS), a radioligand for labeling muscarinic acetylcholine receptors (mAChRs), in membranes of four heart chambers obtained from adult male British United Turkey (BUT) Big 6 (meat-type) and Cro center dot llwitzer (wildtype) turkeys. MAChR subtypes were examined by inhibiting [3H]-NMS binding with subtype selective nonlabelled receptor antagonists. In all left and right atria as well as left and right ventricles of both turkey breeds, the specific [3H]-NMS binding was saturable, reversible and of high affinity (KD range: 0.5-1.0 nM). The maximum receptor density (Bmax) was not significantly different between the four cardiac chambers of BUT Big 6 turkeys, but a significant difference was found between atria and ventricles of Cro center dot llwitzer turkeys. Moreover, significant lower Bmax was found in the atria of Cro center dot llwitzer turkeys than in the atria of BUT Big 6, while the ventricular Bmax was significantly higher. In all cardiac chambers, unlabeled mAChR antagonists competed for specific [3H]-NMS binding sites in a concentration-dependent manner, suggesting the presence of the M3 and M2 receptor subtypes, whereby the latter was the predominant subtype. The presence of the M1 subtype could not be excluded. In conclusion, there was a difference between BUT Big 6 (meat-type) and Cro center dot llwitzer (wild-type) turkeys with regard to receptor density in heart chambers with dominant M2 and M3 receptor subtypes.

Automated summary

This study characterized the specific binding sites for [N-methyl-3H]-scopolamine in membranes of turkey heart chambers, revealing the presence of M2 and M3 receptor subtypes, with M2 being predominant. There were differences in receptor density between BUT Big 6 and Cro center dot llwitzer turkeys in heart chambers.