PRINCIPLES OF OPERATION
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Chapter 8
Patch Clamp
By design, the patch-clamp command voltage is positive if it increases the potential inside
the micropipette. Whether it is hyperpolarizing or depolarizing depends upon whether the
patch is "cell attached", "inside out" or "outside out". The patch-clamp pipette current is
positive if it flows from the headstage through the tip of the micropipette into the patch
membrane.
Cell-Attached Patch
In this mode, the membrane patch is attached to the cell, and the pipette is
connected to the outside surface of the membrane. A positive command voltage
causes the transmembrane potential to become more negative, therefore it is
hyperpolarizing. For example, if the intracellular potential is -70 mV with respect
to 0 mV outside, the potential across the patch is also -70 mV. If the potential
inside the pipette is then increased from 0 mV to +20 mV, the transmembrane
potential of the patch hyperpolarizes from -70 mV to -90 mV.
From the examples it can be seen that the transmembrane patch potential varies
inversely with changes in the command potential, shifted by the resting membrane
potential (RMP) of the cell. A positive pipette current flows through the pipette,
across the patch membrane into the cell. Therefore a positive current is inward.
Inside-Out Patch
In this mode of recording, the membrane patch is detached from the cell, with the
surface that was originally the inside surface exposed to the bath solution. Now the
potential on the inside surface is 0 mV (bath potential). The pipette is still
connected to the outside surface of the membrane. A positive command voltage
causes the transmembrane potential to become more negative, therefore it is
hyperpolarizing. For example, to approximate resting membrane conditions of
V
m
= -70 mV, the potential inside the pipette must be adjusted to +70 mV. If the
potential inside the pipette is increased from +70 mV to +90 mV, the
transmembrane potential of the patch hyperpolarizes from -70 mV to -90 mV.
From the example it can be seen that the transmembrane patch potential varies
inversely with changes in the command potential. A positive pipette current flows
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