References

236 V. Demidchik
progress has been made with respect to molecular characterisation of candidate
genes for NSCC since the first putative plasma membrane NSCC
were discovered in plants (Lam et al. 1998).
16.2
Physiological Roles of Animal NSCC
In animals, NSCC are a diverse group of channels with different structures
and physiological roles (Hescheler and Schultz 1993). A modern NSCC
classification has been published on the web (http://www.neuro.wustl.edu/
neuromuscular/mother/chan.html). These channels play a major role in
recognition of hormones and neurotransmitters and catalyse early cellular
responses to these substances. NSCC are involved in volume regulation,
sensing H + ,Ca 2+ , reactive oxygen species (ROS) and intracellular
cyclic nucleotides. Animal glutamate-, purine-, cyclic-nucleotide-, and
acetylcholine-activated ionotropic receptors are NSCC. They mediate communication
between cells and establish a basis for a high nervous activity.
Depolarisation (due to K + and Na + fluxes) and/or increase in the cytosolic
Ca 2+ activity ([Ca 2+ ]cyt) are frequently consequences of activation of NSCC
at the cellular level. These NSCC-mediated effects can directly or indirectly
(through the second messengers and changes in gene expression) alter
physiological processes at the organismal level.
16.3
Functional Classification of Plant NSCC
Plant NSCC exist both in the plasma membrane and in the tonoplast.
Tonoplast NSCC are well studied at the physiological level in many plant
species (reviewed by Demidchik et al. 2002). Plasma membrane NSCC embrace
(1) constitutive NSCC, (2) ROS-activated NSCC, (3) ligand-activated
NSCC, and (4) mechanosensitive NSCC. Constitutive NSCC are active permanently
without activating factors. Ligand-activated NSCC open after
interaction with a specific chemical substance (ligand). ROS-activated and
mechanosensitive NSCC require the presence of ROS or stretching for
activation, respectively. All these channels vary in biophysical properties
(reviewed by Demidchik et al. 2002).