ATP modulates Na+ channel gating and induces a non-selective cation current in a neuronal hippocampal cell line.
Extracellular ATP evoked two excitatory responses in hippocampal neuroblastoma cells (HN2). The first, an opening of a receptor-operated non-selective cation channel and the second was a leftward shift in Na+ channel activation. Both ATP (5-1000 microM) and 2',3'-(4-benzoyl)-benzoyl-ATP (Bb-ATP, 50 microM) activated a non-selective cation current reversing near 0 mV and shifted the Na+ activation and inactivation curves to the left. Based on a comparison of a series of agonists and antagonists, the inward current appeared to be partially mediated by activation of a P2X7 receptor, although hybrid channels cannot be ruled out. The shift in Na+ channel gating could be separated from the opening of the cation channel, as application of the P2Y antagonist Reactive Blue-2 and GTP shifted the Na+ current activation to the left but failed to elicit the inward cation current. Both responses to ATP and Bb-ATP were insensitive to block by the P2X antagonist suramin (300 microM) but were prevented by incubation in oxidized ATP (200 microM); a putative P2X7 receptor antagonist. Prior screening of the surface negative charge of the membrane with a high concentration of divalent cations prevented both responses. We suggest that ATP4- activates a P2X receptor and becomes trapped on a site, on or near the Na+ channel. Activation of the P2X receptor leads to the opening of a non-specific cation channel, while the binding of ATP4- leads to a modified charge sensed by the Na+ channel, similar to what occurs in the presence of charged amphiphiles as well as a number of beta-scorpion toxins.
El-Sherif
Y
Y
CSI/IBR Center for Developmental Neuroscience and Developmental Disabilities, The College of Staten Island/CUNY, New York, USA.
Wieraszko
A
A
Banerjee
P
P
Penington
N J
NJ
D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D000818:Animals; D002412:Cations / Q000378:metabolism; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000096:biosynthesis* / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*
D002412:Cations; D007473:Ion Channels; D015222:Sodium Channels; D000255:Adenosine Triphosphate