The Electrical Resistance and Capacitance of the Membranes of Nitella translucens

The resistance and capacitance of the membranes of Nitella translucenshave been measured by direct current and alternating currentmethods. Current of the order of 10^-7 amp. was injected intothe cell by means of a conventional Ag, AgCl_-3N KCl glass microelectrodeinserted into the vacuole of the cell. The change of potentialacross the membrane was recorded by two other internal microelectrodeswhich had been inserted into the cell at known distances fromthe current-injecting electrode. In the direct-current experimentsthe input current was in the form of a square pulse, while sinusoidalcurrents of frequency 25 cycles per second were used in thealternating current experiments. The cell was treated as a shortlength of coaxial cable and from the measurements the followingparameters could be obtained: the space constant (), the membraneresistance (R_m) and the membrane capacitance (C_m). The valuesof R_m ranged from 6.7 to 36 K ohm cm.² (mean of 21.4 K ohm cm.²)and those of ranged from 1.5 to 5.7 cm. (mean of 2.6 cm.).The capacitance value was about I µF cm.^-2 These results are discussed within the framework of our knowledgeof these parameters for other cells, particularly plant cells.The measured electrical resistance is shown to be at least tentimes less than the value estimated from the passive fluxesof the principal ions K, Na, and Cl. It is suggested that thisdiscrepancy, which is usually attributed to non-independentmovement of these ions, could be partially explained on electro-osmoticgrounds. The value of the capacitance is very close to thatwhich is usually obtained for other cell membranes. One exceptionallylow value for Nitella has been quoted in the literature. Thereason for the gross error in this particular measurement isgiven.