Abstract-Although Purkinje fibers (PFs) play an important role in cardiac electrophysiology, almost nothing is known about the expression of ion-channel subunits in PFs. We applied competitive reverse transcription-polymerase chain reaction, Western blotting, and immunocytochemistry to compare the expression of ion-channel subunit mRNA and protein in canine PFs versus ventricular muscle (VM). For transient outward current-related subunits, Kv4.2 was not detected, and Kv1.4 expression was extremely low. Kv4.3 expression was of the same order for VM and PFs. The tetraethylammonium chloride-sensitive subunit Kv3.4 was expressed much more strongly in PFs than in VM, and Kv channel-interacting protein transcript expression was 25-fold stronger in VM than in PFs. For delayed rectifiers, ERG and KvLQT1 expression was lower in PFs at both mRNA and protein levels. Although minK transcripts were more numerous in PFs, minK protein was significantly more strongly expressed in VM. L-type Ca 2ϩ current ␣-subunit (Ca V 1.2) and Na ϩ -Ca 2ϩ exchanger proteins were more strongly expressed in VM than in PFs. For T-type Ca 2ϩ current, Ca V 3.1, Ca V 3.2, and Ca V 3.3 transcripts were all more strongly expressed in PFs. For the nonselective cation current, hyperpolarization-activated cation channel 1 (HCN1) expression was subquantifiable, HCN2 transcript expression was comparable in PFs and VM, and HCN4 mRNA expression was strong in PFs but below the detection threshold in VM. HCN2 and HCN4 protein expression was much stronger in PFs than in VM. We conclude that ion-channel subunit expression in PFs differs from that in VM in ways that are consistent with, and shed light on the molecular basis of, well-recognized fundamental PF ionic properties. Key Words: molecular biology Ⅲ cardiac arrhythmias Ⅲ ion currents C ardiac Purkinje fibers (PFs) play an important role in cardiac conduction and arrhythmogenesis. They are particularly significant in generating early afterdepolarizations and triggering transmural reentry in torsade de pointes arrhythmias associated with long QT syndromes. 1-4 PFs also appear important in ventricular tachyarrhythmias that are due to delayed afterdepolarizations, 5 intraventricular reentry, 6 and ventricular fibrillation. 7,8 PF action potentials (APs) have a number of properties that differentiate them from ventricular muscle (VM). They show prominent spontaneous phase-4 depolarization and automaticity 9 ; their AP durations increase much more than those of VM at slow rates, 10,11 leading to preferential PF generation of early afterdepolarizations 1 ; they show prominent rate dependence of phase-1 repolarization 12 ; and they have a more negative plateau voltage. These AP differences likely reflect differences in the density and/or composition of ion channels in PFs compared with VM. Although much is known about the expression of ion-channel subunits in mammalian atrium and VM, the published literature contains very limited data regarding ion-channel subunit expression in PFs. 13 The present study was desig...

Emodin, a natural anthraquinone, has been reported to possess antiproliferative effects in many cancer cell lines. However, anticancer mechanism against human liver cancer remains unclear. In this study, we observed that emodin induced apoptosis in HepG2 cells and caused a significant accumulation of cells in the G1 phase. Western blot data showed that emodin treatment caused the increasing of release of cytochrome c into cytosol from mitochondria and the activation of caspase-8 and caspase-9, which suggest that the intrinsic and extrinsic pathways could be involved. Emodin treatment also resulted in a dose-dependent accumulation of intracellular reactive oxygen species. Furthermore, emodin increased the protein level of p53 and decreased the protein level of NF-κB/p65 in HepG2 cells, which indicated these two regulators might play a role in emodin-induced apoptosis. Computational modeling showed that emodin could directly bind to the BH3 domain of Bcl-2 through forming one hydrogen bond with Ala146 residue in Bcl-2. From these examinations, emodin not only significantly downregulated expression of Bcl-2 but also inhibited the heterodimerization of Bcl-2 with Bax because of strong interaction between emodin and Bcl-2. These suggest that emodin induces apoptosis in liver cancer cell line through a multifaceted complex cascade of events.

Pharmaceutical interactions with human serum albumin (HSA) are of great interest, because HSA is a pharmacokinetic determinant and a good model for exploring the protein-ligand interactions. Due to their hydrophobic nature, naturally occurring flavones, which possess various pharmacological activities, bind to HSA in human plasma. Here, we have identified the binding modes of two representative flavones--baicalin (BLI) and its aglycon, baicalein (BLE)--to HSA using a combination of experimental and computational approaches. The association properties were measured by applying spectroscopic methods, and a higher affinity was found for BLE. As evidenced by displacement and chemical unfolding assays, both ligands bind at Sudlow site I. Furthermore, molecular docking was utilized to characterize the models of HSA-flavone complexes, and molecular dynamics (MD) simulations as well as free energy calculations were undertaken to examine the energy contributions and the roles of various amino acid residues of HSA in flavones binding; the mechanism whereby glycosylation affects the association was also discussed. The present work provides reasonable binding models for both flavones to HSA.