Electrotonic Transmission of an Action Potential between Two Separated Internodal Cells of Chara through a Bridge

Two separated internodal cells of Chara braunii were broughtinto contact with each other longitudinally at their ends andconnected by another pathway composed of a metal bridge beyondthe region of intercellular contact. A conducted action potentialthat arrived at one foot of the bridge electrotonically depolarizedthe other foot of the bridge in the connected cell. The electriccoupling ratio (0.07?0.03), the ratio of the change in the membranepotential of one cell to that of the other cell, was too smallto allow transmission of an action potential. Two cells wereplaced in parallel and connected with two liquid bridges orpools, a' and b'. When the action potential of one cell wasconducted through one connecting pool (pool a)', the other cellwas depolarized electrotonically by the action current via theother connecting pool (pool b'). The coupling ratio was increasedto 0.26?0.07 by the solution bridge, but transmission of theaction potential was rarely observed. Application of 1 mM KC1to pools a' and/or b' slightly improved the frequency of transmissionof the action potential. When pool b' contained 5% urethane,the coupling ratio increased to 0.31?0.08 and transmission ofthe action potential was frequent. (Received August 24, 1989; Accepted March 14, 1990)