Neuromuscular transmission and cholinergic synapses: clinical examples and experimental evidence Flashcards
What did whole cell patch clamping prove?
That ion channels were present in the cell membrane to allow ions to flow and a current to flow
Who completed experiments on the vagus nerve?
Otto Loewi
What was Otto Loewi’s experiment?
perfusion fluid from the heart that had been inhibited by the vagus nerve was moved to another heart with no innervation. The amplitude of beats also decreased
Showed the existence of chemical information, not just the form of electrical impulses
What are MEPPs?
Mini end plate potentials, that occur spontaneously when the motor neurones are not stimulated
Experiment to prove quantal releasE
Katz and Fatt
Incubated neuromuscular synapses in Ringer solution which a lower than normal concentration of calcium. Added extra magnesium to reduce calcium entry into the presynaptic terminal
This caused EPPs to become very small, with slight fluctuations which appeared step like. Showed that the multiples of EPP were in 4s
What else does the experiment show?
Calcium is required for the release of neurotransmitter
How else could the release of calcium be controlled?
Flash photolysis of cages containing calcium
MEPP voltage
0.5 mV
How to prove vesicle release and formation?
Use fluorescent styryl dye to tag membrane of frog neurone
Able to view vesicles either fusing with the membrane or ‘kiss and run[ning]’
How was acetylcholine proven to be in vesicles?
Whittaker homogenised and then centrifuged a sample with many nerve endings, to retrieve the vesicles
when tested, the vesicles contained acetylcholine
How can a nAChR be isolated from the membrane?
Use of alpha bungarotoxin
Evidence for the structure of nAChR
Oocytes injected with mRNA from torpedo electric organs, containing the template required for the formation of the protein subunits to form the channel
a few days later, the oocyte would respond to the application of acetylcholine with rapid depolarisation
More evidence for structure
X ray crystallography and cryocrystallography used to deduce structure
