Tm. Hennessey et al., OXIDANTS ACT AS CHEMOREPELLENTS IN PARAMECIUM BY STIMULATING AN ELECTROGENIC PLASMA-MEMBRANE REDUCTASE-ACTIVITY, Journal of comparative physiology. A, Sensory, neural, and behavioral physiology, 175(5), 1994, pp. 655-665
Paramecium is a valuable eukaryotic model system for studying chemosen
sory transduction, adaptation and cellular sensory integration. While
millimolar amounts of many attractants hyperpolarize and cause faster
forward swimming, oxidants are repellents that depolarize and cause ba
ckward swimming at micromolar concentrations. The non-permeant oxidant
s cytochrome c, nitro blue tetrazolium and ferricyanide are repellents
with half maximal concentrations of 0.4 mu M, 2.2 mu M and 100 mu M r
espectively. In vivo reductase activities follow the same order of pot
encies. The concentration dependence of the cytochrome c reductase act
ivity is well correlated with cytochrome c-induced depolarizations. Th
is suggests that plasma membrane reduction of external cytochrome c is
electrogenic, causing membrane depolarization and chemorepulsion. The
reductase activity also appears to be voltage dependent. Depolarizati
on by either K+, Na+, Ca++ or Mg++ correlates with inhibition of both
in vivo reductase activities and cytochrome c-induced membrane potenti
al changes. These responses were also seen in deciliated cells, showin
g that the body plasma membrane is sufficient for the response. Both c
hloroquine and diphenyleneiodonium inhibited reductase activities but
only at unusually high concentrations. This activity showed no pH depe
ndence in the physiological range. We propose that a plasma membrane b
ound NADPH-dependent reductase controls oxidant-induced depolarization
s and consequent chemorepulsion.