Experimental Techniques: Voltage Clamp Flashcards Preview

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Flashcards in Experimental Techniques: Voltage Clamp Deck (12):
1

What is a Voltage Clamp?

An electrophysiology technique to control (or keep constant) an excitable cell's transmembrane voltage & measure the transmembrane current required to do so.

2

What is a Current Clamp?

An electrophysiology technique to apply a constant or time-varying current to an excitable cell & measure the resulting change in its transmembrane voltage.

3

Why would a Voltage Clamp be used?

  • To measure ion currents: informs about number of open ion channels & their conductance

e.g 1. Measure effects of drugs on ion currents

e.g 2. Estimate contribution of different ion currents to cardiac action potential

  • To control key variable affecting ion channel gating: voltage

4

Why would a Current Clamp be used?

  • To measure transmembrane voltages

e.g 1. Measure voltage changes when mimicking current produced by synaptic input

e.g 2. Record cardiac action potential and effects of ion channel blockers

5

Why measure cardiac action potentials & the ion currents which produce them?

  • Physiological study
  • Pathophysiological study e.g cardiac arrhythmia ventricular fibrillation is often fatal. Electrophysiological mechanisms of VF are influenced by AP characteristics & thus ion currents
  • Pharmacological study e.g how might drugs be anti- or pro-arrhythmic?
  • Computer modelling: provide real experimental data to aid mathematical simulation of highly complex nature of cardiac electrical activity 

6

What are the 3 mechanisms of arrhythmias?

  • Abnormal Automaticity - Favoured by e.g ß-AR stimulation
  • Delayed Afterdepolarisation - Favoured by e.g Intracellular calcium overload
  • Early Afterdepolarisation - Favoured by e.g action potential prolongation

7

During electrophysiological mechanisms of atrial & ventricular arrhythmias, what causes reentry?

Conduction block.

8

What is reentry during atrial & ventricular arrhythmias favoured by?

  • Premature beats
  • Spatial heterogeneity
  • Conduction-slowing
  • Myocardial size increase
  • ERP-shortening (Effective Refractory Period)

9

How is Reentry Circuit Size (wavelength) measured?

RCS = Conduction Velocity x ERP

10

What is Ohms Law?

V = I x R

11

What is the formula for the Nernst equation?

(Electrochemical diffusion potential)

E = RT/zF x ln([ion outside]/[ion inside])

E=Membrane voltage

R=Universal gas constant

T=Absolute temperature

z=Valency of Ion

F=Faraday's constant

12

What is ion selectivity due to?

Channel 2° and 3° structure