Pharmacology (measuring the neuronal membrane potential)

1. @OSAMA_Z96

2. * The Giant axon of Squids :
Is a nerve fiber which radiates from the stellate ganglion, the axon is about 1mm in diameter.
* Tetrodotoxin :
Toxin produced from (Puffer fish), which causes paralysis by affecting the sodium ion transport in both the
CNS & the PNS.
* Lidocaine :
Local anaesthetic (Na+ channel blocker)
* 3,4-diaminopyridine :
Used to treat Lambert-Eaton myasthenic syndrome (LEMS)
* Voltage-clamp technique :
Necessary to :
1- Stabilize the membrane potential at a number of defferent levels.
2- Measure the permeability at those potentials.

3. Puffer fish
Squid

4. 1- To demonstrate the neuronal action potential by electrical stimulation.
2- To demonstrate the neuronal action potential generation & propagation
through the neuron.
3- To investigate the effect of ionic composition (Na & K) concentration on the
nerve action potential in the squid giant axon.
4- To investigate the effect of certain drugs on the nerve action potential in the
squid giant axon.

5. * Drug used in experiment :
1) Tetrodotoxin.
2) Lidocaine.
3) 3,4-Diaminopyridine.
* Salt used in experiment :
1) Sodium ion (Na+).
2) Potassium ion (K+).
* Instrument used in experiment :
1) Microelectrode :
Record pulses.
2) Amplifier.
3) Stimulator :
Stimulate pulses.

7. 50 mV
38 mV
25 mV
15 mV
-56 mV
Na conc.
120 mM
Na conc.
70 mM
Na conc.
50 mM
Na conc.
0
Na conc.
33 mM
K conc.
Will be fixed on
5 mM
Normal AP

8. The action potential is decreases,
(More –ve charge inside the axon).

9. 50 mV
K conc.
5 mM
K conc.
0 mM
K conc.
33 mM
K conc.
70 mMK conc.
50 mM
Na conc.
Will be fixed on
120 mM
Normal AP
-94 mV
-22 mV
-16 mV
-10 mV
0 mV
K conc.
120 mM

10. The action potential is increases,
(More +ve charge inside the axon).

11. 50 mV
Normal AP
Tetrodotoxin
Conc. : 1E-006 M
Lidocaine
Conc. : 1E-006 M
3,4-
Diaminopyridine
Conc. : 1E-006 M
-59 mV
42 mV
46 mV

12. The action potential is decreases,
(Block Na channel and stop action potential propagation).