Channels and Signal Transduction

Neuronal signal transduction is briefly summarized in a simplified version in the following for the reader not being a specialist in neurobiology or neuropharmacology, since a basic knowledge is essential to understand the complex interactions of alkaloids with neuroreceptors, ion channels and signal transduction. Citations in this part of the review have been kept at a minimum and the reader should consult overviews in [17, 38, 42-56] for more details. 

INTERFERENCE OF ALKALOIDS WITH NEUROCEPTORS, ION CHANNELS AND SIGNAL TRANSDUCTION... 

Minke B, Cook B (2002) TRP channel proteins and signal transduction. Physiol Rev 82 429-472... 

Fadool, D. A. and Ache, B. W., Plasma membrane inositol 1,4,5-trisphosphate-activated channels mediate signal transduction in lobster olfactory receptor neurons, Neuron, 9, 907, 1992. 

Yamada T, Endoh T, Suzuki T. 1999. Inhibition of calcium channels by neurocinin receptor and signal transduction in hamster submandibular ganglion cells. J Auton Nerv Syst 76 1-8. 

Shears, S.B., 2000, Inositol pentakis- and hexakisphosphate metabolism adds versatility to the actions of inositol polyphosphates novel effects on ion channels and protein traffic. In Biswas, B.B. and Biswas, S. (eds.), Inositol Phosphates, Phosphoinositides, and Signal Transduction, Subcellular Biochemistry Series, Vol. 26. Plenum Press, New York, pp. 187-226. 

AQP4 is the predominant water channel in the central nervous system (CNS), where it is involved in maintaining brain water balance and neural signal transduction. It is mainly expressed in astroglial cells, which support the neurons. Outside the CNS, AQP4 has been found in the basolateral membrane of renal principal cells as well as in various glandular epithelia, airways, skeletal muscle, stomach, retina and ear. 

The regulation of the total peripheral resistance also involves the complex interactions of several mechanisms. These include baroreflexes and sympathetic nervous system activity response to neurohumoral substances and endothelial factors myogenic adjustments at the cellular level, some mediated by ion channels and events at the cellular membrane and intercellular events mediated by receptors and mechanisms for signal transduction. As examples of some of these mechanisms, there are two major neural reflex arcs (Fig. 1). Baroreflexes are derived from high-pressure barorecep-tors in the aortic arch and carotid sinus and low-pressure cardiopulmonary baroreceptors in ventricles and atria. These receptors respond to stretch (high pressure) or... 

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