Ligand-gated ionic channels are integral membrane proteins that enable rapid and selective ion fluxes across biological membranes. In excitable cells, their role is crucial for generation and propagation of electrical signals. This survey describes recent results from studies performed in the Department of Cellular Neurophysiology, Institute of Physiology ASCR, aimed at exploring the conformational dynamics of the acetylcholine, glutamate and vanilloid receptors during their activation, inactivation and desensitization. Distinct families of ion channels were selected to illustrate a rich
complexity of the functional states and conformational transitions these proteins undergo. Particular attention is focused on structure-function studies and allosteric modulation of their activity. Comprehension of the fundamental principles of mechanisms involved in the operation of ligand-gated ion channels at the cellular and molecular level is an essential prerequisite for gaining an insight into the pathogenesis of many psychiatric and neurological disorders and for efficient development of novel specifically targeted drugs.
Allostery is an essential property of many physiological mechanisms. Cooperativity together with allostery is observed in the behavior of multisubunit receptors. Here we summarize and compare several approaches to the description and analysis of allosteric phenomena with emphasis on the receptors connected to ionic channels as a model. Several simplified methods are discussed in comparison with the microscopic kinetic scheme, affinity-efficacy separation and a thermodynamic approach.
Application of Cerebrolysin (0.1 /rg per 1 ml) by a fast microperfusion system induced an inward current of 0.2 to 1 nA in all neurones from newborn mouse hippocampi held at —30 mV membrane potential. Cerebrolysin- induced currents were reduced by the GABAa antagonist bicuculline (2 /¿M) by 65 %, by the NMDA antagonist aminophosphovaleric acid (APV, 10 /¿M) by 27 %, and by the non-NMDA antagonist cyanonitroquinoxalinedione (CNQX, 10 ¡utA) by 20 %. Cerebrolysin dialyzed through a 3.6 kD gut did not induce any transmembrane current but potentiated the response induced by GABA (10 /utA) to 135 %. We conclude that, in addition to amino acids which activate GABAa, NMDA and non-NMDA receptors, Cerebrolysin also contains a peptide which potentiates the GABAa receptor response.