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curare. Direct stimulations on Nerves----impulse Direct stimulations on Muscles----contraction. Curare +. Curare + stimulation on nerves → muscles’ contraction. X. 1843. Claude Bernard (France) Physiologist

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slide1

curare

Direct stimulations on Nerves----impulse

Direct stimulations on Muscles----contraction

Curare +

Curare + stimulation on nerves → muscles’ contraction

X

1843

Claude Bernard(France)

Physiologist

Interested in mechanism by which nerves stimulate the contraction of skeletal muscles

→Curare somehow acted on the region of contact between the nerve and muscle

slide2

1843→1906

John Langley

Physiologist in Cambridge Uni.

Study the ability of nicotine to stimulate the contraction of muscles and the effect of curare in inhibiting nicotine action

→Impulse should not pass from nerve to muscle by an electric discharge, but by the secretion of a special substance on the end of nerve.

“Chemical transmitter” and “receptive substance”

slide3

1843→1906→1921

Otto Loewi

Physiologist (Austrian-born)

Stimulate the nerve and then transfer the solution to a new heart without vagus, the new heart is inhibited as its own inhibitory nerve have been activated.

→Vagusstoff is acetylcholine(Ach)

slide4

1843→1906→1921→1937

DavidNachmansohn

Neurophysiologist at the Sorbonne

Electric organs of ray are derived from modified skeletal muscle tissue which is rich of acetylcholinesterase (AChase) and nicotinic acetylcholine receptor (nAChR).

slide5

Suitable assay to determine the protein

Chen-YuanLee and his colleagues

National Taiwan Uni.

1963

α-Bungarotoxin in the venom of a Taiwanese snake

slide6

1843→1906→1921→1937→1970s

Isolation of nAChR

Electric organs containing the nAChR

Blend

Homogenate containing the nAChR

Centrifuge

Pellet contains membranes fragments

Triton X-100

Affinity chromatography

Purified nAChR

slide9

1843→1906→1921→1937→1970s

Structure of nAChR

ArthurKarlin (Columbia Uni.)

nAChR is a pentamer. It contains 2 copies of α subunit ,and one copy each of β, γ, and Δsubunit.

4 different subunits are homologous to one another, each subunit containing 4 homologous transmembrane helices.

slide10

1843→1906→1921→1937→1970s

Structure of nAChR

Jean-PierreChangeux (Pasteur Institute)

The receptor acts as both a site for binding ACh and a channel for the passage of cations.

The binding of ACh to the receptor caused a conformational change that opened an ion channel within the protein.

slide11

Sequencing, mutation

Electron microscope

Methods

1843→1906→1921→1937→1970s→pasttwo decades

Structure of nAChR

slide12

1843→1906→1921→1937→1970s→pasttwo decades

Detailed model of nAChR

Nigel Unwin and his colleagues

(Medical Research Council of England)