FURTHER EVIDENCE FOR THE PARALLEL PATHWAY MODEL OF THE METABOLIC CONTROL OF THE ELECTROGENIC PUMP IN NITELLA AS OBTAINED FROM THE HIGH-FREQUENCY SLOPE OF THE ACTION OF LIGHT

Previous investigations of the frequency response of the action of light on the membrane potential in Nitella have revealed 5 time constants and 3 zeros in the range of 2 sec to 20 min. Now, the frequency range is extended by means of filter and correlation techniques to its upper theoretical limit of about 20 Hz. Thus the number of experimentally accessible time constants is increased from 5 to 8, the number of the zeros from 3 to 5. The time constant at 0.01 sec is shown to originate from the electrical impedance of the membrane. The other 7 time constants are labels for the reactions mediating the light effect, and the zeros provide information about the arrangement of these reactions. The new results support and extend the basic concept proposed by Hansen (Hansen, U.-P. 1978;J. Membrane Biol.41: 197) that light acts via three parallel pathways on membrane potential. This model predicts two essential parameters obtained from the high-frequency measurements correctly from the data gained at low frequencies and is capable of reducing the great variety of measured curve shapes of the frequency responses to much smaller changes in two basic parameters. © 1979 Springer-Verlag New York Inc.