Modulation by adenosine of GABA-activated current in rat dorsal root ganglion neurons.
1. The modulation by adenosine of GABA-activated current (IGADA) was studied in freshly isolated rat dorsal root ganglion (DRG) neurons using the whole-cell patch-clamp technique. 2. In most of the DRG neurons examined (68/90, 75.5%) adenosine (1-10 microM) suppressed IGABA, while in some neurons examined, it potentiated (16/90, 17.8%) IGABA. It exerted no effects on IGABA in a few cells (6/90, 6.7%). 3. Adenosine shifted the GABA concentration-response curve downward with no significant change of the EC50. The maximal response to GABA was suppressed by 29.6 +/- 2.6%. The adenosine-induced inhibition of IGABA showed no voltage dependence. 4. 8-Cyclopentyl-1,3-dimethylxanthine (DPCPX; 1 microM), a selective A1 adenosine receptor antagonist, partially reversed adenosine inhibition of IGABA and completely blocked N6-cyclo-hexyladenosine (CHA; an A1 adenosine receptor agonist) inhibition of IGABA. DPCPX (1 microM) also blocked the suppression of IGABA by 2-chloroadenosine (CADO). CGS21680, a selective A2A adenosine receptor agonist, did not inhibit IGABA and DMPX, a selective A2A adenosine receptor antagonist, did not prevent adenosine inhibition of IGABA. 5. Intracellular application of H-7 (20 microM; a protein kinase C inhibitor) reversed adenosine inhibition of IGABA while inclusion of cAMP (1 mM), H-9 (20 microM; a protein kinase A inhibitor) and BAPTA (10 mM; a chelator of calcium ions) in the recording pipette did not affect the depression of IGABA by adenosine. IGABA was also suppressed by internal perfusion of PMA, a protein kinase C activator. 6. The results suggest that adenosine, as a neuromodulator, exerts a modulatory effect on the GABA-induced presynaptic inhibition in primary sensory transmission.
Hu
H Z
HZ
Research Center of Experimental Medicine, Tongji Medical University, Wuhan, The People's Republic of China.
Li
Z W
ZW
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D018756:GABA Antagonists / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists; D005727:Ganglia, Spinal / Q000166:cytology* / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000378:metabolism; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects; D013997:Time Factors
D018756:GABA Antagonists; D058787:GABA-A Receptor Antagonists; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D011963:Receptors, GABA-A; D011493:Protein Kinase C; D000241:Adenosine