PMID- 10228183
OWN - NLM
STAT- MEDLINE
DCOM- 19990622
LR  - 20190508
IS  - 0022-1295 (Print)
IS  - 0022-1295 (Linking)
VI  - 113
IP  - 5
DP  - 1999 May
TI  - Single channel properties of P2X2 purinoceptors.
PG  - 695-720
AB  - The single channel properties of cloned P2X2 purinoceptors expressed in human
      embryonic kidney (HEK) 293 cells and Xenopus oocytes were studied in outside-out 
      patches. The mean single channel current-voltage relationship exhibited inward
      rectification in symmetric solutions with a chord conductance of approximately 30
      pS at -100 mV in 145 mM NaCl. The channel open state exhibited fast flickering
      with significant power beyond 10 kHz. Conformational changes, not ionic blockade,
      appeared responsible for the flickering. The equilibrium constant of Na+ binding 
      in the pore was approximately 150 mM at 0 mV and voltage dependent. The binding
      site appeared to be approximately 0.2 of the electrical distance from the
      extracellular surface. The mean channel current and the excess noise had the
      selectivity: K+ > Rb+ > Cs+ > Na+ > Li+. ATP increased the probability of being
      open (Po) to a maximum of 0.6 with an EC50 of 11.2 microM and a Hill coefficient 
      of 2.3. Lowering extracellular pH enhanced the apparent affinity of the channel
      for ATP with a pKa of approximately 7.9, but did not cause a proton block of the 
      open channel. High pH slowed the rise time to steps of ATP without affecting the 
      fall time. The mean single channel amplitude was independent of pH, but the
      excess noise increased with decreasing pH. Kinetic analysis showed that ATP
      shortened the mean closed time but did not affect the mean open time. Maximum
      likelihood kinetic fitting of idealized single channel currents at different ATP 
      concentrations produced a model with four sequential closed states (three binding
      steps) branching to two open states that converged on a final closed state. The
      ATP association rates increased with the sequential binding of ATP showing that
      the binding sites are not independent, but positively cooperative. Partially
      liganded channels do not appear to open. The predicted Po vs. ATP concentration
      closely matches the single channel current dose-response curve.
FAU - Ding, S
AU  - Ding S
AD  - Department of Chemical Engineering, State University of New York at Buffalo,
      Buffalo, New York 14214, USA.
FAU - Sachs, F
AU  - Sachs F
LA  - eng
PT  - Journal Article
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - United States
TA  - J Gen Physiol
JT  - The Journal of general physiology
JID - 2985110R
RN  - 0 (Cations)
RN  - 0 (Ion Channels)
RN  - 0 (P2RX2 protein, human)
RN  - 0 (Receptors, Purinergic P2)
RN  - 0 (Receptors, Purinergic P2X2)
RN  - 8L70Q75FXE (Adenosine Triphosphate)
RN  - 9NEZ333N27 (Sodium)
SB  - IM
MH  - Adenosine Triphosphate/pharmacology
MH  - Algorithms
MH  - Animals
MH  - Cations/metabolism/pharmacology
MH  - Cell Line
MH  - Electric Stimulation
MH  - Humans
MH  - Hydrogen-Ion Concentration
MH  - Ion Channel Gating/physiology
MH  - Ion Channels/*metabolism
MH  - Kidney/metabolism
MH  - Kinetics
MH  - Membrane Potentials/physiology
MH  - Models, Biological
MH  - Oocytes/metabolism
MH  - Patch-Clamp Techniques
MH  - Receptors, Purinergic P2/*metabolism
MH  - Receptors, Purinergic P2X2
MH  - Sodium/metabolism
MH  - Xenopus
PMC - PMC2222910
EDAT- 1999/05/06 00:00
MHDA- 1999/05/06 00:01
CRDT- 1999/05/06 00:00
PHST- 1999/05/06 00:00 [pubmed]
PHST- 1999/05/06 00:01 [medline]
PHST- 1999/05/06 00:00 [entrez]
AID - 10.1085/jgp.113.5.695 [doi]
PST - ppublish
SO  - J Gen Physiol. 1999 May;113(5):695-720. doi: 10.1085/jgp.113.5.695.