Na+ modulates anion permeation and block of P2X7 receptors from mouse parotid glands.
We previously reported that mouse parotid acinar cells display anion conductance (I(ATPCl)) when stimulated by external ATP in Na+-free extracellular solutions. It has been suggested that the P2X7 receptor channel (P2X7R) might underlie I(ATPCl). In this work we show that I (ATPCl) can be activated by ATP, ADP, AMP-PNP, ATPgammaS and CTP. This is consistent with the nucleotide sensitivity of P2X7R. Accordingly, acinar cells isolated from P2X7R( -/- ) mice lacked I(ATPCl). Experiments with P2X7R heterologously expressed resulted in ATP-activated currents (I(ATP-P2X7)) partially carried by anions. In Na(+)-free solutions, I (ATP-P2X7) had an apparent anion permeability sequence of SCN(-) > I(-) congruent with NO3(-) > Br(-) > Cl(-) > acetate, comparable to that reported for I(ATPCl) under the same conditions. However, in the presence of physiologically relevant concentrations of external Na+, the Cl(-) permeability of I(ATP-P2X7) was negligible, although permeation of Br(-) or SCN(-) was clearly resolved. Relative anion permeabilities were not modified by addition of 1 mM: carbenoxolone, a blocker of Pannexin-1. Moreover, cibacron blue 3GA, which blocks the Na(+) current activated by ATP in acinar cells but not I(ATPCl), blocked I(ATP-P2X7) in a dose-dependent manner when Na+ was present but failed to do so in tetraethylammonium containing solutions. Thus, our data indicate that P2X7R is fundamental for I(ATPCl) generation in acinar cells and that external Na+ modulates ion permeability and conductivity, as well as drug affinity, in P2X7R.
Reyes
Juan Pablo
JP
Instituto de Física, Universidad Autónoma de San Luis Potosí, Dr. Manuel Nava #6, San Luis Potosi, SLP 78290, Mexico.
Pérez-Cornejo
Patricia
P
Hernández-Carballo
Carmen Y
CY
Srivastava
Alaka
A
Romanenko
Victor G
VG
Gonzalez-Begne
Mireya
M
Melvin
James E
JE
Arreola
Jorge
J
D000227:Adenine Nucleotides / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D000838:Anions / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D051379:Mice; D010306:Parotid Gland / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010539:Permeability / Q000187:drug effects; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000502:physiology*; D058486:Receptors, Purinergic P2X7; D012964:Sodium / Q000502:physiology*; D014227:Triazines / Q000494:pharmacology
D000227:Adenine Nucleotides; D000838:Anions; C546468:P2RX7 protein, human; C546469:P2rx7 protein, mouse; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D014227:Triazines; C012842:Cibacron Blue F 3GA; D000255:Adenosine Triphosphate; D012964:Sodium