ABSTRACT
Cell membrane recordings were made in conditions of voltage clamping with tight attachment of the microelectrode-patch clamping--to study the effects of morphine on tetrodotoxin-resistant (TTXr) sodium channels in rat spinal ganglion neurons in culture. The effects of a number of biologically active substances which regulate the receptor-mediated actions of morphine were studied. The effects of morphine were found to involve a chain of sequential reactions leading to decreases in the transfer of effective charge (Zeff) by the activatory gate system of TTXr sodium channels, depending on the concentration of agonist in the extracellular solution. A value of 8 nM was obtained for KD. with a Hill coefficient of X = 0.5. Non-specific antagonists of opioid receptors blocked the actions of morphine; these included ouabain at a concentration of 100 microM. An inhibitor, and activator, and a blocker of G-proteins had no effect on the effective charge. These data provide evidence that morphine decreases the voltage sensitivity of TTXr sodium channels.
Subject(s)
Morphine/pharmacology , Narcotics/pharmacology , Sodium Channels/drug effects , Sodium Channels/physiology , Animals , Cells, Cultured , Drug Resistance , Electrophysiology , Enzyme Inhibitors/pharmacology , Ganglia, Spinal/cytology , Ganglia, Spinal/metabolism , Ion Channel Gating/physiology , Models, Neurological , Naloxone/pharmacology , Narcotic Antagonists/pharmacology , Neurons/metabolism , Osmolar Concentration , Ouabain/pharmacology , Patch-Clamp Techniques , Rats , Rats, Wistar , Receptors, Opioid/physiology , Sodium-Potassium-Exchanging ATPase/antagonists & inhibitors , Tetrodotoxin/pharmacologyABSTRACT
The depolarizing agent veratridine was shown to affect the level of neurotrophic substances in combined cultures of neonatal rat hippocampus and chick embryo spinal ganglia. In this experimental model, the level of neurotrophic factors in rat hippocampus explants increased as a result of increases in neuronal activity mediated by veratridine. The effects of these neurotrophins on neurite growth in the sensitive spinal ganglion neurons in the combined cultures were evaluated using morphometric methods. Neurite-stimulating effects were seen when veratridine was added to the nutritive medium at a concentration of 90 nM. Antibody to nerve growth factor blocked the action of veratridine. These results demonstrate a role for neuron activity as a regulatory mechanism controlling the expression of neurotrophins.
