[Cyclic nucleotides and inosine triphosphate as biochemical modulators of receptor domain ion channel permeability]

Different pathways of control over the permeability of ionic channels in the receptor domains (RD) of biological membranes and their possible functional role in various receptor systems are discussed. It is suggested that cyclic mononucleotides and inositol-triphosphate may directly act as biochemical modulators of such permeability by blocking the Ca(2+)-binding sites of the gate mechanisms of RD ionic channels by recruiting, in particular, Ca2+ within the cell from both intracellular calcium depots and the intercellular medium. Kinetic schemes of gate mechanisms for all possible types of RD ionic channels have been proposed for a case when, in addition to Ca(2+)-ions, the reaction medium contains another type of ions or molecules capable of blocking only one Ca(2+)-binding site of the gate mechanism. Such kinetic schemes form the basis for qualitative and quantitative analyses of cyclic mononucleotide and inositol-triphosphate influence on the permeability of RD ionic channels.