Cardiac Sympathetic Remodeling And The Effect And Mechanism Of Carbon Nanotubes On The Potassium Channel

Cardiac sympathetic nerve remodeling is frequently observed in many diseases. However the mechanisms underlying sympathetic nerve remodeling-associated cardiac electrophysiological instability and ventricular fibrillation are not well understood. One aim of our study was to investigate the linkage of sympathetic denervation, K+ channel remodeling and cardiac arrhythmia. We developed a rat model of chemical sympathectomy by subcutaneous injections of 6-hydroxydopamine (6-OHDA). Cardiac sympathetic innervation was visualized by a glyoxylic catecholaminergic histofluorescence method. Transient outward current (I_to) of ventricular myocytes was recorded with the whole-cell configuration of the patch clamp technique. We found that sympathectomy 1) decreased cardiac sympathetic nerve density and norepinephrine level; 2) reduced the protein expression of Kv4.2, Kv1.4 and Kv channel-interacting protein 2 (KChIP2); 3) decreased current densities and delayed activation of I_to channels; 4) reduced the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB); and 5) increased the severity of ventricular fibrillation induced by rapid pacing. Three weeks after 6-OHDA injections to allow sympathetic regeneration, cardiac sympathetic nerve density and norepinephrine level, expression levels of Kv4.2, KChIP2 proteins and I_to current densities were partially normalized and ventricular fibrillation severity was decreased. We conclude that chemical sympathectomy downregulates the expression of selective Kv channel subunits and decreases myocardial I_to channel activities, contributing to the elevated susceptibility to ventricular fibrillation.A second aim of this study was to investigate the effect of NMDA receptor activation on I_to Channel activity. We previously found that the expression of myocardial NMDA receptors were significantly upregulated in a rat model of cardiac nerve sprouting. Based on these findings, we investigated the relationship of NMDA recepor activation and I_to current. We incubated cardiomyoctes from 10-14-day rats with NMDA, and recorded the I_to current of these cells with whole-cell configuration of patch clamp technique. We further investigated the effects of NMDA on the activities of the four complexes of the respiratory chain in the mitochondria using fluorometer and estimated the production of ATP by bioluminescent methods. The results showed that acute treatment with NMDA suppressed the activities of the four complexes of the respiratory chain and reduced the production of ATP in the mitochondria of rat cardiomyoctes. These results suggest that NMDA receptor activation decreases myocardial I_to channel activities, suppresses the energy metabolism and induces mitochondrial dysfunction, contributing to the elevated susceptibility to ventricular fibrillation.A third aim of this study was to observe the effect of carbons nanotubes on K+ channels on PC12 cells. Nowadays, carbon nanotube research is one of the hotspots in nano research and was considered a potential carrier of drugs and vaccines. However, the side effects of carbon nanotubes are less known. For example, the interaction between carbon nanotubes and cell ion channels is still not well established. In this study, we investigated the effect of multile-walled carbon nanotubes (MWNT) on three types of K+ currents (I_to, I_K and I_K1) in PC12 cells. We incubated PC12 cells with MWNT and recorded the I_to, I_K, I_K1 currents of PC12 cells at different times with whole-cell configuration of the patch clamp technique. We also investigated the effects of MWNT on mitochondrial membrane potential (ΔΨm) and intracellular calcium ([Ca²⁺]_i) level. We found thatMWNT 1) decreased the current densities of I_to, I_K and I_K1, 2) increased the [Ca²⁺]_i and 3)reduced mitochondrial membrane potential (ΔΨm). These results suggest that MWNT in aqueous suspension could suppress potassium channel activities in undifferentiated PC12 cells, and these effects may be associated with mitochondrial dysfunction and oxidativestress.