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 solut...

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Bibliographic Details
Published in:The Journal of membrane biology 1995-11, Vol.148 (1), p.91-98
Main Authors: Naumov, A P, Kaznacheyeva, E V, Kuryshev, Y A, Mozhayeva, G N
Format: Article
Language:English
Subjects:
Adenosine Triphosphate - pharmacology
Animals
Calcium - metabolism
Calcium Channels - metabolism
Cell Membrane
Cell Membrane Permeability - drug effects
Cells, Cultured
Electric Conductivity
GTP-Binding Proteins - physiology
Guanosine 5'-O-(3-Thiotriphosphate) - pharmacology
Guanosine Triphosphate - pharmacology
Ion Transport
Macrophages - metabolism
Male
Membrane Potentials
Patch-Clamp Techniques
Rats
Rats, Wistar
Receptors, Purinergic P2 - physiology
Sodium - metabolism
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Summary: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.
ISSN:0022-2631
DOI:10.1007/BF00234160