The effect of neostigmine, hexamethonium and methyllycaconitine on large-conductance cation channels in the nuclear membrane of cerebellar purkinje neurons of rats

Abstract

Large-conductance cation channels (LCC-channels) were found in both (inner and outer) nuclear membranes of cerebellar Purkinje neurons. They are the most common type of intracellular spontaneously active ion channels among other identified. Their structure and physiological functions are still unknown, but the previous findings confirmed their sensitivity to a number of agonists/antagonists of nicotinic acetylcholine receptors. The purpose of the investigation was to estimate the effect of other regulators of the N-cholinoreceptors functioning – neostigmine, hexamethonium, and methyllycaconitine (MLA) on the LCC-channels in the nuclear membrane of cerebellar Purkinje neurons of rats. The effect of the agents was estimated based on changes in the following biophysical parameters: current amplitude, Po, channel flickering effect. Ion currents through single channels were registered using the patch-clamp technique in a nucleus-attached mode in voltage-clamp configuration. Among the studied substances, only MLA and hexamethonium influenced the LCC-channels functioning. Hexamethonium at a concentration of 2 mM reduced the Po of the LCC-channels by 46%. Under the influence of MLA, a slight effect of channel flickering was observed ("Poisson surprise" was 2.14 in the control and 3.81 under the influence of 200 μM of the substance respectively). No significant change of the biophysical characteristics of the LCC-channels under the influence of neostigmine was detected. Despite the low efficiency as LCC-channels blockers, the lack or only slight effect is a strong argument in favor of the substance usage in medicine due to their wide therapeutic potential. The severity of their effects is necessary for a comprehensive analysis of the effect patterns of the abovementioned substances on the molecular dynamics of the studied channels. The results will also be important for the identification or synthesis of new and more effective inhibitors of the LCC-channels.