Evaluation of Ca2+ permeability of nicotinic acetylcholine receptors in hypothalamic histaminergic neurons.
Hypothalamic histaminergic tuberomammillary (TM) neurons express nicotinic acetylcholine receptors (nAChRs) with kinetic and pharmacological properties resembling those of highly Ca(2+) permeable alpha7 nAChRs. However, the Ca(2+) permeability of TM nAChR channels has not been determined. To directly evaluate the Ca(2+) permeability of TM nAChRs, patch-clamp recordings were conducted using non-cultured acutely dissociated TM neurons and external solutions containing low (2 mM) and high (20 mM) concentrations of Ca(2+). A shift in the reversal potentials was determined from the current-voltage relationships and the permeability ratio, P(Ca)/P(Na), was estimated within the Goldman-Hodgkin-Katz constant field approximation. TM nAChRs were found to be highly Ca(2+) permeable with the permeability ratio, P(Ca)/P(Na)(nAChR) being approximately 5.9 and the fractional Ca(2+) current, P(f)(nAChR) being approximately 10.1% at -60 mV. As a positive control for the applied methods and analysis, the permeability ratio, P(Ca)/P(Na)(NMDAR) being approximately 8.3 and the fractional Ca(2+) current, P(f)(NMDAR) being approximately 13.6% at -60 mV for NMDA receptors were determined using non-cultured acutely dissociated hippocampal pyramidal neurons and found similar to previously reported values. Therefore, these results demonstrate that native TM nAChRs are highly Ca(2+) permeable, but approximately 1.4 fold less permeable to Ca(2+) than native hippocampal pyramidal NMDA receptors.
Uteshev
Victor V
VV
Southern Illinois University School of Medicine, Department of Pharmacology, Springfield, IL 62794, USA. vuteshev@siumed.edu
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D007031:Hypothalamus; D008297:Male; D009474:Neurons; D018408:Patch-Clamp Techniques; D011188:Potassium; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
C579165:Chrna7 protein, rat; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D011188:Potassium; D002118:Calcium