Synaptic transmissionSzinaptikus folyamatok

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A Chord konduktancia -egyenlet The Chord
Conductance equation
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Ohms law I current U electrical
potential R resistance g
conductance Em membrane potential EK
equilibrium potential for K ENa equilibrium
potential for Na
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In the steady-state (no change in current), the
sum of all individual currents through the
membrane (i.e., through individual channels) are
assumed to be zero. MEANING NO NET ION CHARGE
MOVES ACROSS THE MEMBRANE. (INa) (IK)
(ICl-) (ICa2) 0 If we say that the
total conductance gT is the sum of all
conductances, then gT (gNa) (gK) (gCl-)
(gCa2) the above can be solved for the
membrane potential.
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Relative conductances of the membrane
under RESTING conditions gK gt gNa gt
gCl- gt gCa2 (gCl- and gCa2 are really small
and are usually not considered in
calculations)
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The Chord Conductance Equation can be used to
calculate Em if the conductances of each ion and
their Nernst potentials are known.
Note This equation predicts that if a particular
ion has a high conductance relative to the
others, the Em will be near the Nernst potential
of that ion. Thus, if a membrane is permeable to
only K (i.e., gK is high and close to gT), then
the last 3 terms of the above equation will drop
out and Em EK.
.. But the best approximation is achieved when
considering Na and K
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A chord konduktancia egyenlet The chord
conductance equation
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A chord konduktancia egyenlet The chord
conductance equation
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Em EK
A chord konduktancia egyenlet Na csatorna
blokkoló után Chord conductance equation after
blockade of Na channels
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Mechanisms for opening Ion Channels

• Ion channels open in response to
• 1 a voltage stimulus
• Known as voltage-gated channels
• 2 Binding of a ligand
• Known as ligand-gated channels
• 3 a mechanical stimulus
• Known as mechanically gated channels

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Control of Ion Channels
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Patch Clamp Technique

• Lehetové teszi a membránon keresztüli ionáramok
  és feszültség, valamint a membránkapacitás
  mérését.
• It allows to measure transmembrane ion currents
  and voltages as well as changes in membrane
  capacitance.

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Single Channel Recording
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MicroelectrodesMikroelektródák
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Looking through the microscopeKép a mikroszkóp
alatt
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Cell-attached Gigaseal
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ConfigurationsKonfigurációk
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Single Channel RecordingEgyes ioncsatorák
vizsgálata
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Whole Cell RecordingTeljes sejt mérés
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AZ AKCIÓS POTENCIÁL KIALAKULÁSA DEVELOPMENT OF
ACTION POTENTIAL A SZINAPTIKUS
ÁTTEVODÉS SYNAPTIC TRANSMISSION
Dr. Zsembery Ákos
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AKCIÓS POTENCIÁL ACTION POTENTIAL Gyors membrán
potenciál változás, melyet a nyugalmi
potenciálhoz való visszatérés követ Rapid change
in the membrane potential followed by a return to
the resting membrane potential
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Különbözo típusú akcióspotenciálok Different
Types of Action Potentials
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Az akcióspotenciál fázisai Phases of the Action
Potential
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Action Potential and Ion Conductivity in Nerve
and Skeletal Muscle Cells
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Nerve Cells

• have a resting potential - set by a
  constitutively active K-selective channel (leak
  K channel)
• have voltage-gated Na channels
• have voltage-gated K channels

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Az idegsejtek akciós potenciáljának
kialakulásában a feszültség-függo Na és K
csatornák játszák a foszerepet Voltage-gated Na
and K channels are the major players in
generating nerve action potentials
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Feszültség-függo Na csatornák Voltage-gated Na
channels

• Very few types
• Mostly one role
• Initiate and propagate action potentials
• Structure well known
• Three types of conformational state
• controlled by membrane voltage (resting,
• activated and inactivated)

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Na Channel Structure
I
II
III
IV
Outside
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Na Channel Conformations
(at negative potentials -90 mV)
(shortly after more depolarized potentials -90
- 35 mV)
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Na Channel Gating
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Outside
Inside
Na
Na
Na
Na
Na
Na
Na
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Feszültség-függo K csatornák Voltage-gated K
channels

• Many types
• E.g. nerve K channels
• Many roles
• E.g. action potential repolarization
• Structure is known
• Four subunits form homotetramer
• Two types of conformational states
• controlled by membrane potential (closed and
  open)

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Two Conformations
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Voltage Dependent Gating
Outside
S1
S2
S3
S4
S5
S6
Inside
HO2C
H2N
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K Channel Gating
K
K
K
K
K
K
K
Outside
Inside
K
K
K
K
K
K
K
K
K
K
K
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The Action Potential Na and K Channels
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The Nerve Action Potential

• is a transient reversal of the polarity of the
  membrane potential
• has a rising phase (depolarization) caused by the
  opening of Na channels
• has an overshoot that approaches VNa
• has a falling phase (repolarization) caused by
  opening of K channels and inactivation of Na
  channels

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A TEA és a TTX hatásai az akciós
potenciálra Effects of TEA and TTX on the action
potential
TEA Tetraethylammonium TTX tetrodotoxin
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Refrakter fázisok Refractoriness
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A küszöbinger változása a refrakter fázisok
alatt Changes in Threshold During Refractory
Periods
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The Nerve Action Potential

• has an absolute refractory period because most
  Na channels are first rapidly opening and then
  rapidly becoming inactivated
• has a relative refractory period because some Na
  channels are inactivated and some K channels are
  open
• propagates in one direction along axons through
  the sequential action of Na channels
  (unidirectional)