337 - Properties of single calcium channels in the neuronal membrane

The development of the intracellular perfusion technique made isolated nerve cells an extremely convenient object for the detailed study of calcium channels, which allow the corresponding ions to enter the cell through the surface membrane during excitation. A wide range of investigations conducted in this object has shown that calcium channels, allowing the passage of bivalent cations in the order of preference Ba greater than Sr greater than Ca greater than Mg, bind these ions with the aid of a binding group located inside the channel. Other bivalent cations (Co, Ni, Mn, Cd), which bind too strongly with this group, become competitive channel blockers. In the absence of bivalent cations in the extracellular medium the calcium channels lose their selectivity and begin to transmit monovalent cations effectively; the reason for this transformation is detachment of the bound calcium ions from a special regulating group at the mouth of the calcium channels. Calcium channels can exist in two functional states: conducting and nonconducting. The transition between these states is accompanied by movement of charges inside the membrane ("gating currents"). The statistical kinetics of this transition, like the kinetics of gating currents, can be described by a modified Hodgkin-Huxley equation, with an activation variable raised to the power of 2. During long-term membrane depolarization the calcium channels pass into an inactivated state, which is connected with the recurrent blocking action of calcium ions, entering the cell, on the channels. Meanwhile, for some types of calcium channels, potential-dependent activation analogous to that in sodium or potassium channels is observed.

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Activation kinetics of single high-threshold calcium channels in the membrane of sensory neurons from mouse embryos

Kostyuk

Shuba

Teslenko

1989

J. Membrain Biol.

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Activation kinetics of single high-threshold inactivating (HTI or N-type) calcium channels of cultured dorsal root ganglion cells from mouse embryos was studied using a patch-clamp method. Calcium channels displayed bursting activity. The open-time histogram was single exponential with an almost potential-independent mean open time tau op = 1.2 msec. The closed-time histogram was multicomponent; at least three of the components were associated with the activation process. The "fast" exponential component with the potential-independent time constant tau fcl = 0.9 msec included all intraburst gaps, while two "slower" ones with potential-dependent time constants tau scl and tau vscl described shut times between bursts and between clusters of bursts. The burst length histogram was biexponential. The "fast" component with a relatively potential-independent time constant tau fbur = 0.6 msec described short, isolated channel openings while the "slow" component characterized real bursts with a potential-dependent mean life time. The waiting-time histogram could be fitted by a difference of two exponentials with time constants being the same as tau scl and tau vscl. The data obtained were described in the frame of a 4-state sequential model of calcium channel activation, in which the first two stages are formally attributed to potential-dependent transmembrane transfer of two charged gating particles accompanying the channel transitions between three closed states, and the third one to fast conformational changes in channel protein leading to the opening of the channel. The rate constants for all transitions were defined. The validity of the proposed model for both low-threshold inactivating (LTI or T-type) and high-threshold noninactivating (HTN or L-type) calcium channels is discussed.

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337 - Properties of single calcium channels in the neuronal membrane

Cited by 5 publications

References 11 publications

Kinetic Characteristics of Different Calcium Channels in the Neuronal Membrane

Kinetic Characteristics of Different Calcium Channels in the Neuronal Membrane

Calcium channels in the cell membrane

Activation kinetics of single high-threshold calcium channels in the membrane of sensory neurons from mouse embryos

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