Study On The Role Of TRPM7 In The Electrical Remodeling Of Atrial Fibrillation In Human

BackroundAtrial fibrillation (AF) is the most sustained arrhythmia in human, causing an increasing motility and mortality. Presently available therapeutic approaches have limited efficacy and certain potential to cause adverse effects. Thus, new mechanistic knowledge is essential to therapeutic innovation. There are 4 principal pathophysiological mechanisms contributing to the triggering and maintenance of AF:electrical remodeling, structural remodeling, autonomic nervous system changes, and Ca2+handling abnormalities. Electrical remodeling is the key to the occurrence and maintenance of AF. The importance of intracellular Ca2+ handling abnormalities has been highlighted because of the induction of DAD-related spont aneous atrial ectopic activity and regulation of the activities of key Ca2+-handling proteins such as LTCC, RyR2, and PLB. Transient receptor potential melastatin-7 (TRPM7) is one of non-selective cation channels with the ionic permeability of calcium. Recent study has demonstrated the TRPM7 channel protein expressed in human atrial fibroblasts, which mediate Ca2+ signals and confer fibrogenes in humans with atrial fibrillation. Meanwhile, Trpm7 is critical for myocardial proliferation during early cardiogenesis. Moreover, recently there has been evidence for the functional TRPM7 channels present in human atrial myocytes. Thus, we hypothesized TRPM7 may be involved in intracellular Ca2+ handling of the atrial cardiomyocyte and lead to the electrical remodeling of atrial fibrillation.ROS (reactive oxygen species) are closely associated with atrial fibrillation. Hydrogen peroxide (H2O2) is one of the important ROS. Previous study has demonstrated H2O2 is associated with arrhythmias. It can enhance the L-type Ca2+ current, inactivate of the Na+ current, inducing EADs, DADs and triggered activities. Besides, previous researches have revealed that H2O2 has an effect on the anoxic neuronal and cardiac fibroblasts, but whether the channel on cardiomyocyte membrane could be affected by H2O2 is unknown. Thus, we hypothesized that H2O2 may affect the TRPM7 on cardiomyocyte membrane as it on the anoxic neuronal or cardiac fibroblasts and play a role in atrial electrical remodeling.Objective1. To elucidate the effect of TRPM7 channel on the atrial cardiomyocyte membrane in the electrical remodeling of AF.2. To investigating whether H2O2 is involved in the atrial electrical remodeling by affecting the electropharmacology of TRPM7 channel.Materials and MethodsSingle atrial myocytes from right atrial specimens collected during the cardiac surgery were isolated by an improved two-step enzymatic method. The TRPM7 channel was recorded under whole-cell patch-clamp configuration. Use immunohistochemical technique to examine the protein of TRPM7 in the human atrial myocytes. The change of TRPM7 protein expression and mRNA lever between SR and AF groups were evaluated with Real-time PCR and western blot analysis. Use the whole-cell patch-clamp configuration to observe the change of the TRPM7 current before and after adding 500 μmol/L H2O2.Results1. TRPM7 current of human atrial myocytes in SR and AF groupsComparison of the TRPM7 channel currents between SR and AF groups:Statistically significant differences of channel currents density was observed and the TRPM7 current density in the AF group is significantly higher than that in the SR group under the voltage from-120 mV to-50 mV and+40 mV to+80 mV (P<0.05).2. TRPM7 protein expression and mRNA lever of human atrial myocytes between the SR group and AF groupTRPM7 protein expression and mRNA lever of human atrial myocytes in the AF group was significantly higher than in the SR group (P<0.05).3. Effect of H2O2 on the regulation of the TRPM7 currentAdd H2O2 to the bath solution and record the current until steady state. After adding H2O2, the current density of TRPM7 channel was significantly decreased under the voltage from-120 mV to-110 mv and 30 mv to 80 mv (P<0.05).Conclusions1. TRPM7 channel seems to play a role in the electrical remodeling of AF.2. Both mRNA and protein level of TRPM7 channel are elevated in AF patients, which may provide the molecular biological basis for the electrical remodeling of AF.3. H2O2 can inhibit the current of the TRPM7 channel and may be involved in the atrial electrical remodeling.