18 Questions
What is the characteristic of channel gating mentioned in the text?
Binary, existing either in conducting or non-conducting state
What type of channels are always open and non-gated?
Leak channels
What causes a change in the conformation of stretch-sensitive channels?
Increase in membrane tension
Which statement best describes the behavior of stochastic channel gating?
Opening and closing are random on a millisecond time scale
What is the primary factor that leads to the loss of channel conductance after activation for certain types of channels?
Inactivation, such as voltage-gating
Which mechanism gates voltage-gated channels according to the text?
Movement of a charged segment influenced by membrane potential
What aspect of ion channel gating can be deduced from the analysis of point amplitude histogram?
Number of open channels
How do voltage-activated channels respond to high transmembrane potentials?
Increase in the open probability
What influences the gating of voltage-gated channels?
Movement of a charged segment (voltage sensor)
What can drugs like lidocaine and verapamil do in relation to ion channels?
Modulate gating by activation and blocking
Which type of current analysis helps deduce channel properties through 'fluctuation analysis'?
Point amplitude histogram
What does 'C' represent in the context of channel gating?
Closed state of a channel
In the context of channel gating, what does the term 'stochastic' refer to?
Random and unpredictable transitions
Based on the provided information, what is the formula for calculating the open probability of a channel?
$\alpha$ / ($\alpha$ + $\beta$)
What distribution is used to represent the dwell time at the open state of a channel?
Exponential distribution
How is the average dwell time for the channel remaining in the closed state calculated?
$1 / \alpha$
The rate constants α and β are determined through fitting the ____________.
Dwell time histograms
What kind of kinetics is described by first-order kinetics in modeling single channel behavior?
Microscopic gating kinetic model
Study Notes
Channel Gating
- Channel gating is binary, existing either in conducting (open) or non-conducting (close or inactivated) state.
- Types of channel gating:
- Voltage-gated: change in membrane potential leads to a change in channel conformation.
- Ligand-gated: specific ligand binding to specific sites leads to conformational change.
- Stretch-sensitive (mechanical-sensitive): change in membrane tension alters conformation of channel.
- Leak (non-gated): constitutively open ion channels, e.g., leak K channel.
Stochastic Channel Gating
- Ion channel transits between open and closed states stochastically on a millisecond time scale due to agitation by thermal energy.
- Channel gating exhibits randomness and brief opening and closing.
Gating Current
- Gating current is generated by the movement of charged segments of the channel (voltage sensor) in response to changes in transmembrane potential.
- Gating current can be measured.
Point Amplitude Histogram
- The point amplitude histogram can be fitted with a sum of Gaussian distributions to estimate the single channel current (or conductance) and channel open probability.
Pharmacology for Channel Gating
- Drugs can modulate channel gating by activating and blocking ion channels, e.g., Na channel blockers (lidocaine) are local anaesthetics, and Ca channel blockers (verapamil) are used to treat hypertension.
Microscopic Channel Kinetics
- Single channel behavior can be modelled by first-order kinetics:
- α: rate constant for transition from closed to open state.
- β: rate constant for transition from open to closed state.
- The open and closed probabilities of the channel can be calculated.
- The average dwell time for the channel remaining in the open or closed state can be calculated.
- The probability density function for the dwell time at open or closed state follows an exponential distribution.
Dwell Time Histogram
- Dwell time histograms can be fitted to estimate the rate constants α and β.
Test your knowledge on stochastic channel gating, gating mechanisms, gating current, open probability, macroscopic gating kinetics model, and more in the field of bioelectricity. This quiz is based on the teachings of Faculty Chen Peng from the School of Chemistry, Chemical Engineering and Biotechnology (CCEB) at NTU.
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