guanosine-diphosphate and barium-chloride

To elucidate the mechanisms of antinociception mediated by the dopaminergic descending pathway in the spinal cord, we investigated the actions of dopamine (DA) on substantia gelatinosa (SG) neurons by in vivo whole-cell patch-clamp methods. In the voltage-clamp mode (V(H)=-70mV), the application of DA induced outward currents in about 70% of SG neurons tested. DA-induced outward current was observed in the presence of either Na(+) channel blocker, tetrodotoxin (TTX) or a non-NMDA receptor antagonist, CNQX, and was inhibited by either GDP-β-S in the pipette solution or by perfusion of a non-selective K(+) channel blocker, Ba(2+). The DA-induced outward currents were mimicked by a selective D2-like receptor agonist, quinpirole and attenuated by a selective D2-like receptor antagonist, sulpiride, indicating that the DA-induced outward current is mediated by G-protein-activated K(+) channels through D2-like receptors. DA significantly suppressed the frequency and amplitude of glutamatergic spontaneous excitatory postsynaptic currents (EPSCs). DA also significantly decreased the frequency of miniature EPSCs in the presence of TTX. These results suggest that DA has both presynaptic and postsynaptic inhibitory actions on synaptic transmission in SG neurons. We showed that DA produced direct inhibitory effects in SG neurons to both noxious and innocuous stimuli to the skin. Furthermore, electrical stimulation of dopaminergic diencephalic spinal neurons (A11), which project to the spinal cord, induced outward current and suppressed the frequency and amplitude of EPSCs. We conclude that the dopaminergic descending pathway has an antinociceptive effect via D2-like receptors on SG neurons in the spinal cord.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; 6-Cyano-7-nitroquinoxaline-2,3-dione; Action Potentials; Afferent Pathways; Animals; Barium Compounds; Chlorides; Dopamine; Dopamine Agents; Drug Interactions; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Guanosine Diphosphate; Male; Nociceptors; Pain; Patch-Clamp Techniques; Physical Stimulation; Quinpirole; Rats; Rats, Sprague-Dawley; Skin; Sodium Channel Blockers; Spinal Cord; Substantia Gelatinosa; Tetrodotoxin; Thionucleotides

An appropriate mixture of ethylene glycol and BaCl2 enhanced the otherwise very low intrinsic GTPase activity of the elongation factor 2 isolated from the archaeon Sulfolobus solfataricus (SsEF-2). The enzymatic activity became up to 300-fold higher than that of the SsEF-2 GTPase measured in the absence of any stimulator, but remained 20-fold lower than that stimulated by ribosome. The stimulatory effect of ethylene glycol/Ba2+ was attributed to the increased affinity for GTP, probably related to a conformational change occurring in a hydrophobic region near the catalytic site.

Topics: Adenosine Diphosphate Ribose; Alcohols; Barium Compounds; Binding Sites; Cations, Divalent; Chlorides; Ethylene Glycol; Ethylene Glycols; GTP Phosphohydrolase-Linked Elongation Factors; GTP-Binding Proteins; Guanosine Diphosphate; Guanosine Triphosphate; Guanylyl Imidodiphosphate; Hydrogen-Ion Concentration; Hydrolysis; Peptide Elongation Factor 2; Peptide Elongation Factors; Sulfolobus; Temperature

We studied the effects of internal and external solutions on potassium currents in frog atrial cells. Experiments were carried out in whole cell recording in the presence of tetrodotoxin and cobalt in the bath to suppress the inward currents. In the absence of pyruvate and glucose in the external solution, a time-independent current increased progressively in a few minutes till the death of the cell. This current had the properties of the ATP-sensitive potassium current IK(ATP) in mammalian cells. In the presence of pyruvate and glucose in the external solution, the membrane current stayed low for 30 min. Addition of guanosine monophosphate (GMP, 40 microM), guanosine triphosphate (GTP, 40 to 1000 microM), adenosine diphosphate (ADP, 40 microM) or adenosine triphosphate (ATP, 3000 microM) to the internal solution had no major effect on the current amplitude. In contrast, addition of GDP (20 or 40 microM) produced a loss of rectification in a few minutes. The current activated by GDP was time independent as was the current observed in the absence of glucose and pyruvate. It was sensitive to cesium and barium, it was blocked when ATP was added to GDP in the internal solution, and it was suppressed by the sulphonylurea glibenclamide (1 microM). We suggest that GDP produced a local depletion of ATP, by displacement of the equilibrium between ATP, GDP, ADP and GTP. This hypothesis is supported by the fact that the current activated by GDP was rapidly suppressed when adding GTP in excess to the internal solution.

Topics: Adenosine Triphosphate; Animals; Barium; Barium Compounds; Cells, Cultured; Cesium; Chlorides; Dialysis; Electric Conductivity; Glucose; Glyburide; Guanosine Diphosphate; Heart Atria; Myocardium; Potassium; Potassium Channels; Pyruvates; Rana esculenta