Regulation by equilibrative nucleoside transporter of adenosine outward currents in adult rat spinal dorsal horn neurons.
A current response induced by superfusing adenosine was examined in substantia gelatinosa (SG) neurons of adult rat spinal cord slices by using the whole-cell patch-clamp technique. In 78% of the neurons examined, adenosine induced an outward current at -70 mV [18.8 +/- 1.1 pA (n = 98) at 1mM] in a dose-dependent manner (EC(50) = 177 microM). A similar current was induced by A(1) agonist N(6)-cyclopentyladenosine (1 microM), whereas A(1) antagonist 8-cyclopentyl-1,3-dipropylxanthine (1 microM) reversed the adenosine action. The adenosine current reversed its polarity at a potential being close to the equilibrium potential for K(+), and was attenuated by Ba(2+) (100 microM) and 4-aminopyridine (5mM) but not tetraethylammonium (5mM). The adenosine current was enhanced in duration by equilibrative nucleoside-transport (rENT1) inhibitor S-(4-nitrobenzyl)-6-thioinosine (1 microM) and adenosine deaminase (ADA) inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (1 microM), and slowed in falling phase by adenosine kinase (AK) inhibitor iodotubercidine (1 microM). We conclude that a Ba(2+)- and 4-aminopyridine-sensitive K(+) channel in SG neurons is opened via the activation of A(1) receptors by adenosine whose level is possibly regulated by rENT1, adenosine deaminase and adenosine kinase. Considering that intrathecally-administered adenosine analogues produce antinociception, the regulatory systems of adenosine may serve as targets for antinociceptive drugs.
Liu
Tao
T
Department of Physiology, Saga Medical School, 5-1-1 Nabeshima, Saga 849-8501, Japan.
Fujita
Tsugumi
T
Kawasaki
Yasuhiko
Y
Kumamoto
Eiichi
E
D015761:4-Aminopyridine / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D033705:Equilibrative Nucleoside Transport Proteins / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D020671:Posterior Horn Cells / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D013376:Substantia Gelatinosa / Q000166:cytology*; D014970:Xanthines / Q000494:pharmacology
D004791:Enzyme Inhibitors; D033705:Equilibrative Nucleoside Transport Proteins; D026902:Potassium Channel Blockers; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D014970:Xanthines; D001464:Barium; C048599:N(6)-cyclopentyladenosine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D015761:4-Aminopyridine; D000241:Adenosine; D011188:Potassium