Rat neuronal nicotinic acetylcholine receptors containing α7 subunit: pharmacological properties of ligand binding and function

Aim: To compare pharmacological properties of heterologously expressed homomeric alpha 7 nicotinic acetylcholine receptors (alpha 7 nAChRs) with those of native nAChRs containing a7 subunit (alpha 7* nAChRs) in rat hippocampus and cerebral cortex. Methods: We established a stably transfected HEK-293 cell line that expresses homomeric rat alpha 7 nAChRs. We studies ligand binding profiles and functional properties of nAChRs expressed in this cell line and native rat alpha 7* nAChRs in rat hippocampus and cerebral cortex. We used [I-125]-alpha-bungarotoxin to compare ligand binding profiles in these cells with those in rat hippocampus and cerebral cortex. The functional properties of the alpha 7 nAChRs expressed in this cell line were studied using whole-cell current recording. Results: The newly established cell line, KX alpha 7R1, expresses homomeric alpha 7 nAChRs that bind [I-125]-alpha-bungarotoxin with a K-d value of 0.38 +/- 0.06 nmol/L, similar to K-d values of native rat alpha 7* nAChRs from hippocampus (K-d=0.28 +/- 0.03 nmol/L) and cerebral cortex (K-d=0.33 +/- 0.05 nmol/L). Using whole-cell current recording, the homomeric alpha 7 nAChRs expressed in the cells were activated by acetylcholine and (-)-nicotine with EC50 values of 280 +/- 19 mu mol/L and 180 +/- 40 mu mol/ L, respectively. The acetylcholine activated currents were potently blocked by two selective antagonists of alpha 7 nAChRs, alpha-bungarotoxin (IC50= 19 +/- 2 nmol/L) and methyllycaconitine (IC50= 100 +/- 10 pmol/L). A comparative study of ligand binding profiles, using 13 nicotinic ligands, showed many similarities between the homomeric alpha 7 nAChRs and native alpha 7* receptors in rat brain, but it also revealed several notable differences. Conclusion: This newly established stable cell line should be very useful for studying the properties of homomeric alpha 7 nAChRs and comparing these properties to native alpha 7* nAChRs.