CYCLIC-NUCLEOTIDES AND INOSITOL TRIPHOSPHATE AS BIOCHEMICAL MODULATORS OF THE RECEPTOR DOMAIN ION-CHANNEL CONDUCTANCE

Different ways of controlling the biological membrane receptor domain (RD) ion channel conductance are considered with special emphasis on functional implications for different receptor systems. Cyclic mononucleotides and inositol triphosphate may act as intracellular biochemical modulators of this conductance by blocking the Ca-binding centers of gating mechanisms of the RD channels, and thereby mobilizing Ca2+ either from the cellular depots or from the extracellular medium. Kinetic schemes are given to illustrate the functions of the channel gating mechanisms in all possible types of RD when, in addition to Ca2+, the medium contains another ion or molecule capable of blocking only one Ca-binding site of the gating mechanism at a time. In particular, these kinetic schemes may provide a basis for qualitative and quantitative analyses of influence exerted by cyclic mononucleotides and inositol triphosphate on permeability of the PD ion channels.