Crab Axons showing a Prolonged Repolarization Phase

Abstract

A FURTHER type of response from isolated crab axons has been recorded by a new technique. The method is to thread an isolated axon through two holes in a fine polythene tube. The axon outside the tube is treated with isotonic sucrose solution and then raised into paraffin oil. Inside the tube test solutions can be flowed over the axon membrane. The effect is to produce an isolated ‘node’ of excitable membrane. Non-polarizable potassium chloride wick electrodes provide stimulating and recording connexions on each side of the ‘node’. This method gives the normal variety of responses from different fibres¹. In one type of fibre, when bathed by normal sea-water, the action potential shows a very prolonged repolarization phase of 25 msec with two discrete segments of 1 msec and of 24 msec, and during the later segment a supernormality develops, that is, during the falling phase of the first action potential a second action potential can be elicited by a weaker stimulus. The absolute refractory period extends for a period of 2 msec, up to the end of the first phase of the repolarization. Following this for 3—5 msec a period of typical subnormality leads to the period of supernormality which can last as long as 30 msec (Figs. 1 and 2 a and b).