Related Experiment Video
Updated: Aug 5, 2026
Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes
Published on: January 10, 2011
The effect of permeant ions on single calcium channel activation in mouse neuroblastoma cells: ion-channel
Y M Shuba1, V I Teslenko, A N Savchenko
1A. A. Bogomoletz Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev.
Abstract:
1. Single low-threshold inactivating (LTI or T-type) Ca2+ channels of undifferentiated neuroblastoma cells (clone N1E-115) were investigated using the patch-clamp technique. 2. Single-channel conductance, gi, for Ca2+, Sr2+ or Ba2+ as a permeant cation was similar (7.2 pS). Mean channel open time, tau op, was also practically independent of the divalent ion species; it decreased from 0.7 to 0.3 ms between -40 and 0 mV. 3. Modification of the calcium channel selectivity by lowering the external Ca2+ concentration to 10(-8) M produced an increase in gi for Na+ and Li+ ions and a shift of potential-dependent characteristics in the hyperpolarizing direction. Voltage sensitivity and absolute values of tau op were also changed. These changes were dependent on both permeant monovalent ion type and concentration. 4. At high [Na+]o, tau op was almost potential independent (congruent to 0.3 ms). Decrease in [Na+]o and substitution of Li+ for Na+ increased tau op and the steepness of its potential dependency. 5. The divalent and monovalent cations that were tested had much smaller effect on the mean intraburst shut time, tau cl(f), which was nearly independent of membrane potential (congruent to 0.6 ms). By contrast, mean burst duration was strongly potential dependent and noticeably affected by permeant ion type. 6. All kinetic changes were analysed in terms of a four-state sequential model for channel activation. According to this model the channel enters the open state through three closed states. Transitions between closed states can be formally related to the transmembrane movement of two charged gating particles (m2 process). The interaction between ion flux and a sterical region of the Ca2+ channel selectivity filter may, depending on ion transfer rate and ionic radius, lead to a local increase of the dielectric constant, resulting in redistribution of the electric field and changes in potential dependency of tau op.
Insights
Researchers studied low-threshold inactivating (LTI) calcium channels in neuroblastoma cells. They found that changing ion concentrations altered channel behavior, impacting its electrical properties and opening times.
Area of Science:
- Neuroscience
- Cell Biology
- Biophysics
Background:
- Low-threshold inactivating (LTI), also known as T-type, calcium channels play crucial roles in neuronal excitability.
- Understanding the biophysical properties of these channels is essential for comprehending neuronal function and dysfunction.
Purpose of the Study:
- To investigate the single-channel properties of LTI Ca2+ channels in neuroblastoma cells.
- To examine the influence of different permeant cations (divalent and monovalent) on channel kinetics and conductance.
Main Methods:
- Utilized the patch-clamp technique to record single LTI Ca2+ channel activity.
- Manipulated external ion concentrations (Ca2+, Na+, Li+) to assess their effects on channel gating and ion permeation.
Main Results:
- Single-channel conductance was similar for Ca2+, Sr2+, and Ba2+.
- Mean open time (tau op) was largely independent of divalent ion species but sensitive to monovalent ion type and concentration, shifting in a hyperpolarizing direction.
- Intraburst shut time was minimally affected by ions, while burst duration was significantly influenced by permeant ion type and membrane potential.
Conclusions:
- The kinetic behavior of LTI Ca2+ channels is modulated by the type and concentration of permeant monovalent ions.
- A four-state sequential model, involving a 'm2 process' for gating particle movement, can explain the observed kinetic changes.
- Ion flux interactions with the channel's selectivity filter may alter the local dielectric constant, affecting voltage-dependent gating.
Related Concept Videos
01:24Non-gated Ion Channels
Compared to the gated ion channels, the non-gated channels, also known as leakage or passive channels, have no gating mechanism.
01:19The Role of Ion Channels in Neuronal Computation
Sometimes a single EPSP is strong enough to induce an action potential in the postsynaptic neuron. However, multiple presynaptic inputs must often create EPSPs around the same time for the postsynaptic neuron to be sufficiently depolarized to fire an action potential.
01:19Ligand-gated Ion Channels
Three Subfamilies of Ligand-gated Ion Channels
Ligand-gated ion channels fall into three subfamilies. The 'Cys-loop' includes the nicotinic acetylcholine receptors, γ-aminobutyric acid (GABA), glycine, and 5-hydroxytryptamine receptors. The second one is the 'Pore-loop' channels that include the...
01:26Voltage-gated Ion Channels
Generally, all voltage-gated ion channels have a 'voltage-sensing domain' that spans the lipid bilayer. The charged residues in the sensor move in response to the membrane potential changes that open the channel allowing ions movement. There are several types of...
01:30Ligand-Gated Ion Channel Receptor: Gating Mechanism
01:19Ligand-gated Ion Channels
Three Subfamilies of Ligand-gated Ion Channels
Ligand-gated ion channels fall into three subfamilies. The 'Cys-loop' includes the nicotinic acetylcholine receptors, γ-aminobutyric acid (GABA), glycine, and 5-hydroxytryptamine receptors. The second one is the 'Pore-loop' channels that include the...