The effects of various ions on the resting membrane potential of the giant axons of Myxicola were determined. The mean resting potential in artificial sea water is 69 mv, inside negative. The membrane potential decreases with increasing external potassium concentrations, while changes in the sodium and chloride concentrations have little or no effect. For potassium concentrations greater than 50 mM/L the relation between membrane potential and concentration approximates that of a perfectly selective potassium electrode. The data for the whole range of con- centrations examined can be well fitted by the equation:
It was pointed out that the Myxicola giant axons can be studied under space voltage clamp and can be made available in the laboratory for 12 months out of the year. Myxicola then should become a very useful preparation for the study of membrane phenomena.
Much of the present degree of understanding of the nature of excitable membranes is based on data and analyses obtained from the giant axon, of the squid (Curtis and Cole, '42; Hodgkin and Huxley, '52; Baker et al., '62; Chandler and Meves, '65). The utility of this preparation has been due chiefly to its suitability for observation using the space voltage clamp technique (Cole, '49; Hodgkin et al., '52). A limitation on the utility of squid is that they are available only seasonally and do not survive well in the laboratory.
Recently, Binstock and Goldman ('67) reported experiments on another preparation, also suitable for observation using a space voltage clamp, the giant axon of the polychaete Myxicola infundibulum. Voltage clamped current records and current voltage relations obtained from Myxicola seem to be similar in every respect to those obtained from the squid. MyxicoZa, however, may be made available in the laboratory for 12 months out of the year and should, therefore, become an extremely important preparation for the study of membrane phenomena.
Binstock and Goldman have presented data indicating that the early transient current seen under voltage clamp, and presumably the depolarization phase of