Whole-cell vs Cell-attached patch

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Outline

1. Whole-cell vs Cell-attached patch
2. Current Clamp
3. Components of an action potential
4. Voltage Clamp
5. Conductances of an action potential
6. Channel Structure
7. Single channel recordings

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Cell-attached Patch
Whole-cell Patch
GOhm Seal between pipet and membrane
Pipet and cell are contiguous
Record single channels Monitor spiking
Measure macro currents Synaptic events
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
Membrane time constant RmC
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
Slope I/Vm g (conductance) 1/g Rm
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
-55 mV
Activation of Ih
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Current Clamp
Done in whole-cell configuration Monitors the
potential of the cell- therefore units will be in
volts By convention V Einside Eoutside Upward
deflections are depolarizing downward are
hyperpolarizing
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Action Potentials
The Hodgkin-Huxley Model The squid giant axon
action potential had only sodium and potassium
currents. Other cells action potentials are
shaped by a number of other conductances.
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Beyond Hodgkin-Huxley Action Potentials
Storm, 1987
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Voltage Clamp
Used to measure currents that underlie changes in
potential ITotal IIonic IC where IC
C(dV/dt) Thus, by clamping the cell at a certain
voltage, dV/dt0 and IT II Measures the amount
of current needed to hold the cell at a given
potential- therefore units will be in amps
Downward (negative deflections) are inward
currents upward are outward
L-Type Calcium Channel
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Voltage Clamp
Series resistance is due to the resistance of the
extracellular solution (Ohms) and the access
through the pipet tip (MOhms).
Voltage Clamp errors 1. Current across Rs
causes a voltage drop. 2. R in series with C
forms a low-pass filter.
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Hodgkin and Huxley, 1952
Different conventions 1. Vrest 0 mV not -60
mV 2. Negative potentials are depolarizing 3.
Inward currents are positive
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Hodgkin and Huxley, 1952
TAIL CURRENTS allow you to isolate voltage and
time dependent properties of a channel from the
driving force on the ion.

1. Activation
2. Inactivation
3. Recovery from inactivation
4. Deactivation

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Single Channel Recordings
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Increased Input R Can locally apply drugs
extracellularly
Can expose intracellular domain of channel to
variable solutions
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Things to look for

• Ion concentrations in internal and external
  solutions
• Temperature