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Dihydropyridine-sensitive low-threshold calcium channels in isolated rat hypothalamic neurones
N Akaike1, P G Kostyuk, Y V Osipchuk
1Department of Neurophysiology, Tohoku University, School of Medicine, Sendai, Japan.
The Journal of Physiology
|May 1, 1989
Summary
This study characterizes low-voltage-activated calcium channels in rat hypothalamic neurons, detailing their activation, inactivation, and blockade by various ions and drugs.
Area of Science:
- Neuroscience
- Electrophysiology
- Pharmacology
Background:
- Low-voltage-activated calcium channels (LVA Ca2+ channels) play a crucial role in neuronal excitability.
- Understanding the properties of LVA Ca2+ channels in specific neuronal populations, like those in the ventromedial hypothalamus, is essential for comprehending neural function.
- These channels are implicated in various physiological processes and neurological disorders.
Purpose of the Study:
- To investigate the electrophysiological properties of low-voltage-activated calcium channels in rat ventromedial hypothalamic neurons.
- To characterize the activation, inactivation, and ion substitution effects on these channels.
- To determine the potency of various inorganic cations and organic calcium antagonists in blocking LVA Ca2+ channel currents.
Main Methods:
- Whole-cell patch-clamp recording using a suction-pipette technique for internal perfusion and voltage clamp.
- Application of a concentration-jump technique for rapid drug application.
- Recording of transient inward calcium currents evoked by step depolarizations from a hyperpolarized holding potential.
Main Results:
- A low-threshold transient inward calcium current, distinct from high-threshold currents, was identified in ventromedial hypothalamic neurons.
- The activation and inactivation kinetics were highly voltage-dependent, with rapid activation and inactivation observed at more positive potentials.
- The current amplitude was dependent on external calcium concentration and was modulated by barium and strontium ions. Various di- and trivalent cations and organic calcium antagonists effectively blocked the current, with distinct potencies.
Conclusions:
- Low-voltage-activated calcium channels in rat ventromedial hypothalamic neurons exhibit unique electrophysiological properties.
- These channels are sensitive to voltage, extracellular calcium concentrations, and are potently blocked by specific inorganic cations and organic calcium antagonists.
- The findings provide crucial insights into the functional role of LVA Ca2+ channels in hypothalamic neuronal activity and potential therapeutic targets.