Importance of Cationic Channels for Functioning of the Nuclear Envelope of Neurons as a Calcium Store
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The membrane of the endoplasmic reticulum is, in fact, an extension of the nuclear envelope of eukaryotic cells; both these compartments can fulfill the function of intracellular calcium stores. Using a patch-clamp technique, we studied the biophysical properties of the channels expressed in the inner nuclear membrane of pyramidal neurons of the rat hippocampal CA1 area, in particular of large-conductance cationic channels and calcium channels of inositol trisphosphate receptors (the main channels in membranes of this type). As the results of the measurements showed, the activity of channels of both types demonstrates clearly pronounced voltage dependences. The probability of their open state (P o) depends on the voltage inside the nuclear envelope lumen. At positive potentials, the activity of these channels is significantly more intense than at negative potentials. Moreover, channels of both types are reversibly blocked at considerable negative potentials. We believe that this property of ion channels in the nuclear envelope is an important factor responsible for the control of calcium signals in the cell nucleus. We propose a hypothesis on the mechanism underlying termination of Ca2+ release from such intracellular stores, which is based on the specificity of the voltage dependence of ion channels of the above-mentioned types.
Keywordshippocampal pyramidal neurons nuclear envelope endoplasmic reticulum calcium stores inositol trisphosphate receptors large-conductance cationic channels
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