Activation of the recombinant human alpha 7 nicotinic acetylcholine receptor significantly raises intracellular free calcium.
The alpha 7 nicotinic acetylcholine receptor (nAChR) subtype, unlike other neuronal nicotinic receptors, exhibits a relatively high permeability to Ca++ ions. Although Ca++ entry through this receptor subtype has been implicated in various Ca(++)-dependent processes in the central nervous system, little is known about how this receptor modulates mammalian intracellular Ca++ dynamics. Intracellular Ca++ responses evoked by activation of the human alpha 7 nAChRs stably expressed in HEK-293 (human embryonic kidney) cells were studied. Inward current and intracellular Ca++ transients were recorded simultaneously in response to a fast drug application system. Current recordings under whole-cell voltage-clamp and fast ratiometric intracellular Ca++ imaging acquisition were synchronized to drug pulses. The mean peak [Ca++]i observed with 100 microM (-)-nicotine was 356 +/- 48 nM (n = 8). The magnitude of the intracellular Ca++ elevation corresponds to a 20% fractional current carried by Ca++ ions. The EC50 of the intracellular Ca++ responses for (-)-nicotine, (+/-)-epibatidine, 1,1 dimethyl-4-phenyl-piperazinium and acetylcholine were 51, 3.5, 75 and 108 microM, respectively. These EC50 values strongly correlate with those recorded for the cationic inward current through alpha 7 nAChR. alpha-Bungarotoxin, methyllcaconitine or extracellular Ca++ chelation ablated (-)-nicotine-evoked increase in intracellular Ca++ concentration. This study provides evidence that cation influx through the human alpha 7 nAChR is sufficient to mediate a significant, transient, rise in intracellular Ca++ concentration.
Delbono
O
O
Department of Physiology and Pharmacology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina, USA.
Gopalakrishnan
M
M
Renganathan
M
M
Monteggia
L M
LM
Messi
M L
ML
Sullivan
J P
JP
D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008969:Molecular Sequence Data; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000502:physiology*; D011994:Recombinant Proteins
D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; D009538:Nicotine; D002118:Calcium