INQUIMAE   12526
INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA
Unidad Ejecutora - UE
artículos
Título:
Responses of Rat P2X2 Receptors to Ultrashort Pulses of ATP Provide Insights into ATP Binding and Channel Gating
Autor/es:
MOFFATT LUCIANO; HUME RICHARD I
Revista:
JOURNAL OF GENERAL PHYSIOLOGY
Referencias:
Año: 2007 vol. 130 p. 183 - 183
ISSN:
0022-1295
Resumen:
To gain insight into the way that P2X2 receptors localized at synapses might function, we explored the properties of outside-out patches containing many of these channels as ATP was very rapidly applied and removed. Using a new method to calibrate the speed of exchange of solution over intact patches, we were able to reliably produce applications of ATP lasting <200 ìs. For all concentrations of ATP, there was a delay of at least 80 ìs between the time when ATP arrived at the receptor and the fi rst detectable fl ow of inward current. In response to 200-ìs pulses of ATP, the time constant of the rising phase of the current was ~600 ìs. Thus, most channel openings occurred when no free ATP was present. The current deactivated with a time constant of ~60 ms. The amplitude of the peak response to a brief pulse of a saturating concentration of ATP was ~70% of that obtained during a long application of the same concentration of ATP. Thus, ATP leaves fully liganded channels without producing an opening at least 30% of the time. Extensive kinetic modeling revealed three different schemes that fi t the data well, a sequential model and two allosteric models. To account for the delay in opening at saturating ATP, it was necessary to incorporate an intermediate closed state into all three schemes. These kinetic properties indicate that responses to ATP at synapses that use homomeric P2X2 receptors would be expected to greatly outlast the duration of the synaptic ATP transient produced by a single presynaptic spike. Like NMDA receptors, P2X2 receptors provide the potential for complex patterns of synaptic integration over a time scale of hundreds of milliseconds. 2 receptors localized at synapses might function, we explored the properties of outside-out patches containing many of these channels as ATP was very rapidly applied and removed. Using a new method to calibrate the speed of exchange of solution over intact patches, we were able to reliably produce applications of ATP lasting <200 ìs. For all concentrations of ATP, there was a delay of at least 80 ìs between the time when ATP arrived at the receptor and the fi rst detectable fl ow of inward current. In response to 200-ìs pulses of ATP, the time constant of the rising phase of the current was ~600 ìs. Thus, most channel openings occurred when no free ATP was present. The current deactivated with a time constant of ~60 ms. The amplitude of the peak response to a brief pulse of a saturating concentration of ATP was ~70% of that obtained during a long application of the same concentration of ATP. Thus, ATP leaves fully liganded channels without producing an opening at least 30% of the time. Extensive kinetic modeling revealed three different schemes that fi t the data well, a sequential model and two allosteric models. To account for the delay in opening at saturating ATP, it was necessary to incorporate an intermediate closed state into all three schemes. These kinetic properties indicate that responses to ATP at synapses that use homomeric P2X2 receptors would be expected to greatly outlast the duration of the synaptic ATP transient produced by a single presynaptic spike. Like NMDA receptors, P2X2 receptors provide the potential for complex patterns of synaptic integration over a time scale of hundreds of milliseconds.