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[The Na,K pump regulates a decrease in the cholinosensitivity of the neurons in the snail Helix lucorum taurica Kryn
A S Pivovarov1, D V Boguslavskiĭ
1Department of Higher Nervous Activity, Lomonosov State University, Moscow.
Abstract:
In Helix lucorum snail we studied the effects of ouabain, inhibitor of Na,K-pump, on the depression of cholinosensitivity in command neurons of withdrawal behavior and the role of the intracellular free Ca2+. The cellular analog of the negative learning (habituation) was used Transmembrane integral inward currents were recorded from the identified LPa2, LPa3, RPa3, and RPa2 neurons in ganglia preparation using two-electrode voltage clamp technique. Acetylcholine (ACh) was locally applied iontophoretically. Reduction of neuronal cholinosensitivity was estimated as a depth of depression of the ACh-induced inward current during rhythmic local application of ACh (interstimulus interval of 1-3 min) onto the somatic membrane. Bath application of ouabain (0.1 mM) produced an increase in depression in one group of neurons and its decrease in another group. After 60-150 min of spontaneous diffusion of a calcium ion chelator BAPTA (1 mM) from the intracellular microelectrode, ouabain produced only the increase in depression. If CaCl2 (100 mM) was added to the solution of the voltage-recording intracellular microelectrode, 60 min later ouabain produced only the reduction of the depression of the ACh current. The conclusion is drawn that the inhibition of the Na,K-pump by ouabain modifies the depression of neuronal cholinosensitivity in the cellular analog of habituation. The direction of the modulatory effect depends on the basal concentration of the intracellular free Ca2+.
Insights
Ouabain, a Na,K-pump inhibitor, alters cholinosensitivity in snail neurons during habituation. The effect depends on intracellular free calcium levels, influencing learning and memory processes.
Area of Science:
- Neuroscience
- Cellular Physiology
- Behavioral Science
Background:
- Neuronal cholinosensitivity is crucial for withdrawal behaviors.
- Habituation, a simple form of learning, involves changes in neuronal responses.
- The Na,K-pump and intracellular calcium play roles in neuronal excitability and plasticity.
Purpose of the Study:
- To investigate the effect of ouabain, a Na,K-pump inhibitor, on cholinosensitivity.
- To determine the role of intracellular free Ca2+ in modulating this effect.
- To explore the cellular mechanisms underlying habituation in Helix lucorum.
Main Methods:
- Two-electrode voltage clamp technique on identified Helix lucorum neurons (LPa2, LPa3, RPa3, RPa2).
- Recording transmembrane inward currents in response to iontophoretically applied acetylcholine (ACh).
- Assessing cholinosensitivity by measuring the depression of ACh-induced currents during rhythmic stimulation.
Main Results:
- Ouabain (0.1 mM) caused variable effects on cholinosensitivity depression, increasing it in some neurons and decreasing it in others.
- Intracellular BAPTA (calcium chelator) led to ouabain consistently increasing depression.
- Intracellular CaCl2 led to ouabain consistently reducing depression.
- The modulatory effect of ouabain on cholinosensitivity depression is dependent on basal intracellular free Ca2+ concentration.
Conclusions:
- Inhibition of the Na,K-pump by ouabain modulates neuronal cholinosensitivity depression during habituation.
- The direction of ouabain's modulatory effect is determined by the baseline intracellular free calcium concentration.
- This study highlights the interplay between ion transport, calcium homeostasis, and learning in the nervous system.