Selectivity of ATP-activated GTP-dependent Ca(2+)-permeable channels in rat macrophage plasma membrane.
Outside-out configuration of the patch clamp technique was used to test whether an intracellular application of G protein activator (GTP gamma S) affects ATP-activated Ca(2+)-permeable channels in rat macrophages without any agonist in the bath solution. With 145 mM K+ (pCa 8.0) in the pipette solution, activity of channels permeable to a variety of divalent cations and Na+ was observed and general channel characteristics were found to be identical to those of ATP-activated ones. Absence of extracellular ATP makes it possible to avoid the influence of ATP receptor desensitization and to study the channel selectivity using a number of divalent cations (105 mM) and Na+ (145 mM) as the charge carriers. Permeability sequence estimated by extrapolated reversal potential measurements was: Ca2+:Ba2+:Mn2+:Sr2+: Na+:K+ = 68:30:26:10:3.5:1. Slope conductances (in pS) for permeant ions rank as follows: Ca2+:Sr2+: Na+:Mn2+:Ba2+ = 19:18:14:12:10. Unitary Ca2+ currents display a tendency to saturate with the Ca2+ concentration increase with apparent dissociation constant (Kd) of 10 mM. No block of Na+ permeation by extracellular Ca2+ in millimolar range was found. The data obtained suggest that (i) activation of some G protein is sufficient to gate the channels without the ATP receptor being occupied, (ii) the ATP receptor activation results in the gating of a special channel with the properties that differ markedly from those of the receptor-operated or voltage-gated Ca(2+)-permeable channels on the other cell types.
Naumov
A P
AP
Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia.
Kaznacheyeva
E V
EV
Kuryshev
Y A
YA
Mozhayeva
G N
GN
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D002462:Cell Membrane; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002478:Cells, Cultured; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000502:physiology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D017136:Ion Transport; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018048:Receptors, Purinergic P2 / Q000502:physiology; D012964:Sodium / Q000378:metabolism
D015220:Calcium Channels; D018048:Receptors, Purinergic P2; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D012964:Sodium; D019204:GTP-Binding Proteins; D002118:Calcium