Coupling of human nicotinic acetylcholine receptors alpha 7 to calcium channels in GH3 cells.
The neuronal nicotinic acetylcholine receptor alpha7 (nAChR alpha7) may be involved in cognitive deficits in Schizophrenia and Alzheimer's disease. A fast pharmacological characterization of homomeric alpha7 receptors is mostly hampered by their low functional expression levels in heterologous expression systems. In the present study expression of homomeric nAChR alpha7 was achieved in GH3 rat pituitary cells. Alpha7 subunits were heterologously expressed as components of [125I]-labeled alpha-bungarotoxin binding nAChRs (Bmax: 1.2 pmol/mg protein). Function of the expressed alpha7 ion channels was assessed by patch-clamp recording and calcium imaging. While acetylcholine-induced currents desensitized within much less than 1 s, calcium-sensitive fluorescence transients peaked after 5-10 s and returned to background levels within 30 s only. The fluorescence signal was blocked by isradipine and removal of extracellular sodium indicated that in these cells opening of rapidly desensitizing alpha7 nAChR triggers calcium influx via voltage-gated, DHP-sensitive calcium channels. In this cellular system, agonists revealed the following rank order of potency: epibatidine>anatoxin A>AAR17779>ABT-594>DMPP>nicotine>GTS-21>cytisine>ABT-418>acetylcholine>choline>ABT-089. All of the signals were inhibited by the alpha7 antagonists alpha-bungarotoxin (pIC50: 7.4) and methyllycaconitine (pIC50: 7.8). Further, marketed antidepressants showed antagonistic activity with the following rank order of potency: fluoxetine>imipramine>paroxetine>sertraline. These data illustrate that coupling to voltage-gated calcium channels allows a rapid and reliable functional examination of nAChR alpha7.
Feuerbach
Dominik
D
Neuroscience Research, Novartis Institutes for BioMedical Research, CH 4002 Basel, Switzerland. dominik.feuerbach@pharma.novartis.com
Lingenhöhl
Kurt
K
Dobbins
Peter
P
Mosbacher
Johannes
J
Corbett
Nicola
N
Nozulak
Joachim
J
Hoyer
Daniel
D
D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D006801:Humans; D017275:Isradipine / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002121:Calcium Channel Blockers; D015220:Calcium Channels; C579167:Chrna7 protein, human; C579165:Chrna7 protein, rat; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D017275:Isradipine