Membrane properties of the giant muscle fiber of the barnacle Balanus nubilus were studied by controlling the ionic composition of the external and internal media. The resting potential decreases with increasing external K-concentration, K(+)(out), and decreasing internal K-concentration, K(+)(in), over a considerable range. Spike potentials are elicited when the internal calcium ions are removed, and the overshoot is determined by the ratio between Ca(++)(out) and K(+)(in) and not by the external or internal Na(+).
Hagiwara et al. (1964) studied this question.