Acetyl-L-carnitine induces a sustained potentiation of the afterhyperpolarization.
Acetyl-L-carnitine is known to improve many aspects of the neural activity even if its exact role in neurotransmission is still unknown. This study investigates the effects of acetyl-L-carnitine in T segmental sensory neurons of the leech Hirudo medicinalis. These neurons are involved in some forms of neural plasticity associated with learning processes. Their physiological firing is accompanied by a large afterhyperpolarization that is mainly due to the Na+/K+ ATPase activity and partially to a Ca2+ -dependent K+ current. A clear-cut hyperpolarization and a significant increase of the afterhyperpolarization have been recorded in T neurons of leeches injected with 2 mM acetyl-L-carnitine some days before. Acute treatments of 50 microM acetyl-L-carnitine induced similar effects in T cells of naive animals. In the presence of apamin, a pharmacological blocker of Ca2+ -dependent K+ channel, acetyl-L-carnitine still enhanced the residual afterhyperpolarization, suggesting an effect of the drug on the Na+/K+ATPase. Acetyl-L-carnitine also increased the hyperpolarization induced by intracellular injection of Na+ ions. Therefore, acetyl-L-carnitine seems to be able to exert a positive sustained effect on the Na+/K+ ATPase activity in leech T sensory neurons. Moreover, in these cells, widely arborized, the afterhyperpolarization seems to play an important role in determining the action potential transmission at neuritic bifurcations. A computational model of a T cell has been previously developed considering detailed data for geometry and the modulation of the pump current. Herein, we showed that to a larger afterhyperpolarization, due to the acetyl-L-carnitine-induced effects, corresponds a decrement in the number of action potentials reaching synaptic terminals.
Lombardo
P
P
Department of Physiology and Biochemistry G. Moruzzi, University of Pisa, Via S. Zeno 31, 56127, Italy.
Scuri
R
R
Cataldo
E
E
Calvani
M
M
Nicolai
R
R
Mosconi
L
L
Brunelli
M
M
D000108:Acetylcarnitine / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D005724:Ganglia / Q000166:cytology / Q000187:drug effects; D007267:Injections; D007865:Leeches; D008959:Models, Neurological; D009473:Neuronal Plasticity; D009475:Neurons, Afferent / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology; D013569:Synapses / Q000502:physiology; D014110:Touch / Q000502:physiology*
D000108:Acetylcarnitine; D000254:Sodium-Potassium-Exchanging ATPase