Investigação da correlação de longo alcance na cinética de canais iônicos formados pela gramicidina A em membranas artificiais

Abstract

Ion channels are integral proteins present in cell membranes, being fundamental components in a wide variety of physiological processes, e.g. propagation of the nervous impulse, muscular contraction, control of the cardiac excitability and cellular secretion. The ion channels shift between different states of conductance, sometimes allowing, sometimes interrupting the flow of ions between the cellular compartments. The mechanism of opening and closing ion channels has been modeled as a random process, however, some studies have shown that these transitions in some channels have memory, that is, long-term correlation. Gramicidin A (gA) is a pentadecapeptide produced by Bacillus brevis with the ability to form simple ion channels when inserted into lipid membranes. The structural simplicity, the ability to form channels and the ease of molecular manipulation of gA have made gramicidin a good model for studies of ion channels. There is a large amount of reports about gA channels, however, we did not find studies using mathematical methods of nonlinear dynamics in the analysis of the existence of memory in these channels. In this context we used the Detrended Fluctuation Analysis (DFA) and the Approximate Entropy (ApEn) in the investigation of the existence of memory and complexity in the kinetic process of the gA channels, respectively. The single-channel currents were recorded in real time through a microcomputer coupled to an A / D converter and a patch-clamp amplifier. All experiments were performed under the following experimental conditions: diphytanoyl phosphatidylcholine planar lipid bilayers in 1 M NaCl solution not buffered, initial pH of 6.3 ± 0.2; the transmembrane potential of 200 mV and a temperature of 25 ° C. The conductance of the gA channel was 15.5 ± 0.05 pS. The time constants, , for the gA channel for the open and closed state were 𝑓== 3.1866 ± 0.1752 s and 𝑎= 12.0743 ± 0.8658 s, respectivel. According to the number of events and percentage deletion of time series regions, different behaviors in kinetics of gA channels were observed: antipersistent correlation (𝛼𝐷𝐹𝐴 = 0.4 and 0.44), persistent correlation (𝛼𝐷𝐹𝐴 = 0.63) and presence of random behavior (𝛼𝐷𝐹𝐴 = 0.53 ± 0.2). However, it has been observed in most of the analyzed series that the kinetics of these channels tend to exhibit a random behavior. The results of the ApEn analyzes showed that the series that have random behavior presented greater complexity when compared to the series that have memory. The results obtained allow us to conclude that the kinetic process of the gA channel has high complexity and absence of memory, divergent behavior from those found in many structurally complex ion channels, such as some sodium and potassium channels, which have a deterministic behavior.