Na%2b modulates anion permeation and block of P2X7 receptors from mouse parotid glands Article uri icon

abstract

  • We previously reported that mouse parotid acinar cells display anion conductance (IATPCl) when stimulated by external ATP in Na %2b-free extracellular solutions. It has been suggested that the P2X7 receptor channel (P2X7R) might underlie I ATPCl. In this work we show that IATPCl can be activated by ATP, ADP, AMP-PNP, ATPγS and CTP. This is consistent with the nucleotide sensitivity of P2X7R. Accordingly, acinar cells isolated from P2X7R-/- mice lacked IATPCl. Experiments with P2X7R heterologously expressed resulted in ATP-activated currents (IATP-P2X7) partially carried by anions. In Na %2b-free solutions, IATP-P2X7 had an apparent anion permeability sequence of SCN- > I- ≅ NO -3 > Br- > Cl- > acetate, comparable to that reported for IATPCl under the same conditions. However, in the presence of physiologically relevant concentrations of external Na%2b, the Cl- permeability of IATP-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%2b current activated by ATP in acinar cells but not IATPCl, blocked IATP-P2X7 in a dose-dependent manner when Na%2b 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%2b modulates ion permeability and conductivity, as well as drug affinity, in P2X7R. © 2008 Springer Science%2bBusiness Media, LLC.

publication date

  • 2008-01-01