Sir Alan Hodgkin and the Giant Axon of the Atlantic Squid

Alan Hodgkin

Alan Hodgkin

On February 5, 1914, English physiologist and biophysicis Sir Alan Lloyd Hodgkin was born. Hodgkin shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles for the discovery of the chemical processes involved in nerve conduction, more specifically, discoveries concerning the ionic mechanisms involved in excitation and inhibition in the peripheral and central portions of the nerve cell membrane.

Alan Hodgkin attended Trinity College, Cambridge. He volunteered on Aviation Medicine at Farnborough during the Second World War and was transferred to the Telecommunications Research Establishment (TRE) where he worked on the development of centimetric radar, including the design of the Village Inn AGLT airborne gun-laying system. Hodgkin also flew on the test flight of a Bristol Blenheim fitted with the first airborne centimetric radar system.

Along with the English physiologist and biophysicist Andrew Fielding Huxley, Alan Hodgkin developed an action potential theory representing one of the earliest applications of a technique of electrophysiology. It was also known as the “voltage clamp”. Technically, a voltage clamp iteratively measures the membrane potential, and then changes the membrane potential (voltage) to a desired value by adding the necessary current. The method clamps the cell membrane at a desired constant voltage, allowing the voltage clamp to record what currents are delivered. The voltage clamp allows the membrane voltage to be manipulated independently of the ionic currents, allowing the current-voltage relationships of membrane channels to be studied.

Andrew Fielding Huxley and Alan Hodgkin also used a giant axon of the veined squid, Loligo forbesii. It enabled them to record ionic currents as they would not have been able to do in almost any other neuron, such cells being too small to study using the techniques of the time. The experiments started at the University of Cambridge, beginning in 1935 with frog sciatic nerve, and soon after they continued their work using squid giant axons at the Marine Biological Association Laboratory in Plymouth. In 1939, Alan Hodgkin and Andrew Huxley published a short paper in the journal Nature announcing their achievement of recording action potentials from inside a nerve fibre. The large diameter of the axon provided a great experimental advantage for Hodgkin and Huxley as it allowed them to insert voltage clamp electrodes inside the lumen of the axon. For their work on the squid giant axon, Huxley, and Hodgkin received the Nobel Prize in Physiology or Medicine which was also shared by John Eccles.

Together with Andrew Huxley, Hodgkin established the propagation mechanism of nerve impulse called “action potentials”, the electrical impulses which enable the activity of an organism to be coordinated by a central nervous system. They also were able to hypothesize the existence of ion channels on cell membranes, which were confirmed decades later. Hodgkin was also the discoverer of cell membrane depolarisation sequence now known as the Hodgkin cycle.

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