ATP evokes different currents in TTX-sensitive and TTX-resistant cells of dorsal root ganglia

Modulation of sodium currents in rat sensory neurons by nucleotides

The effects of various nucleotides on the fast tetrodotoxin-sensitive (f-TTX-S) and the slow tetrodotoxin-resistant (s-TTX-R) sodium currents in rat dorsal root ganglion (DRG) neurons were investigated using the patch-clamp technique. Nucleoside triphosphates (NTPs; ATP, GTP, UTP and CTP) and nucleoside diphosphates (NDPs; ADP, GDP, UDP and CDP) decreased f-TTX-S current, whereas they increased s-TTX-R current, when currents were evoked by step depolarizations to 0 mV from a holding potential of -80 mV. NTPs and NDPs shifted both the conductance-voltage relationship curve and the steady-state inactivation curve in the hyperpolarizing direction in both types of sodium currents. Most of them also increased the maximum conductance of s-TTX-R current. ITP, a derivative of ribonucleotide, and dTTP, a deoxyribonucleotide, modulated both types of sodium currents similarly to NTPs and NDPs. However, nucleoside monophosphates (NMPs; AMP, GMP, UMP and CMP) and adenosine had little or no effect on either type of sodium current. Therefore, it seems that nucleotides, regardless of the kind of base, should have two or more phosphates to be able to modulate sodium currents in DRG neurons. Extracellular nucleotides with di- or tri-phosphates would influence the perception by modulating sodium currents in sensory neurons. Particularly, the increase of the maximum conductance and the hyperpolarizing shift of the conductance-voltage relationship of s-TTX-R sodium current would result in an intensified nociception.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ?cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.

ATP modulation of sodium currents in rat dorsal root ganglion neurons

The modulation of tetrodotoxin-sensitive (TTX-S) and slow tetrodotoxin-resistant (TTX-R) sodium currents in rat dorsal root ganglion neurons by ATP was studied using the whole-cell patch-clamp method. The effects of ATP on two types of sodium currents were either stimulatory or inhibitory depending on the kinetic parameters tested. At a holding potential of -80 mV ATP suppressed TTX-S sodium currents when the depolarizing potential was positive to -30 mV but it increased them when the depolarizing potential was negative to -30 mV. At the same holding potential slow TTX-R sodium currents were always increased by ATP regardless of the depolarizing potential. In both types of sodium currents ATP shifted both the conductance-voltage relationship curve and the steady-state inactivation curve in the hyperpolarizing direction, and accelerated the time-dependent inactivation. ATP decreased the maximum conductance of TTX-S sodium currents but increased that of slow TTX-R sodium currents. The results suggest that ATP would decrease the excitability of neurons with TTX-S sodium channels but would increase that of neurons with slow TTX-R sodium channels. The effects of ATP on sodium currents were preserved in the presence of a G-protein inhibitor, GDP-beta-S, or purinergic antagonists, suramin and Reactive Blue-2, suggesting that purinergic receptors might not be involved in ATP modulation of sodium currents.

Effects of ATP on TTX-sensitive and TTX-resistant sodium currents in rat sensory neurons

Differential effects of ATP on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium currents in rat dorsal root ganglion neurons were studied using the whole-cell variation of path-clamp technique. Currents were evoked by step depolarizations to 0 mV from a holding potential of -80 mV. ATP suppressed TTX-S sodium currents while it increased TTX-R sodium currents. The effects were concentration-dependent and were reversible upon washout with ATP-free external solution. ATP-gamma-S, a hydrolysis-resistant ATP analog, also affected two types of sodium currents similarly to ATP, excluding the possibility that the effects were caused by the products of ATP hydrolysis, namely adenosine. ATP by modulating sodium currents may exert profound effects on the transmission of sensory information such as nociception.