Journal of Neurophysiology, Vol 39, Issue 6 1184-1192, Copyright © 1976 by APS
Sensory neurons in leech central nervous system: changes in potassium conductance an excitation threshold
W. R. Schlue
1. The sensory neurons in the leech central nervous system differ in their
accommodation to linearly rising currents. Advantage was taken of these
differences to study the ionic mechanism of accommodation in single pairs
of N (noxious), P (pressure), and T (touch) cells. 2. Nonlinearities in
membrane-potential changes and current-voltage relationships with
square-wave and ramp currents are more pronounced in P and T cells than in
N cells. The accommodation coefficients increase in conditions that reflect
this delayed rectification. When rectification is absent, the accommodation
coefficients depart from unity only slightly or not at all. 3.
Accommodation coefficients remain unchanged when half of the chloride in
the bathing medium is replaced by sulfate. Accommodation coefficients
become greater when the extracellular potassium concentration is reduced
from 4 to 0 mM, and decrease when the concentration is raised to 8 mM. The
membrane potential changes by only a few millivolts. 4. As extracellular
potassium concentration is increased, the action potential is lengthened
and the maximal rate of fall of the action potential is reduced. With
concentrations greater than 4 mM these relationships are linear, but depart
from linearity at lower concentrations. The amplitude of the undershoot
decreases linearly as the extracellular potassium concentration increases
from 4 to 16 mM, and increases non-linearly at concentrations below 4 mM.
5. The rapid accommodation of leech neurons is based primarily on an
increased potassium conductance. The possibility is considered that
concentration changes like those produced experimentally may occur
naturally, affecting integrative processes in the central nervous system.
