Localization of ionic conductances in crayfish muscle fibers.

Analysis of the changes in membrane potential and conductance of isolated crayfish muscle fibers caused by rapid solution changes leads to the following conclusions. First, the extensive invagination system of this fiber presents a barrier for diffusion between bath and sarcolemma that accounts for the time lag of electrical responses to changes in bath chloride concentration. Morphological data regarding these invaginations were used in a model which simulated the fiber response on an analog computer. Second, the potassium conductance is effectively localized on the sarcolemma in direct contact with the bath (superficial sarcolemma), whereas the chloride conductance is restricted to the invaginations. This distribution of conductances is the reverse of that found in frog muscle.