Coxal Muscle Receptors in the Crab: The Receptor Current and Some Properties of the Receptor Nerve Fibres

The resting membrane potential of S and T receptor fibres is usually –50 to – 60 mV and is potassium dependent. The neurone membrane may also be permeable to other ions or some part of it may be inaccessible. The electrical responses of the fibres are nearly ohmic for 40 mV on either side of the resting membrane potential. In some fibres there is a little depolarizing electrogenesis. Receptor potentials were evoked by ‘step’ pulls on the receptor muscle. In response to fast pulls there is often a variable spike component, abolished by tetrodotoxin and presumably therefore sodium dependent. Ion substitution experiments indicate that the rest of the receptor potential is also mainly sodium dependent. However, in the absence of sodium a small receptor response remains. Possible reasons for this are discussed.