Rationale: Inositol 1,4,5-trisphosphate receptors (IP 3 Rs) have been implicated in the generation of arrhythmias and cardiac muscle nuclear signaling. However, in the mammalian sinoatrial node (SAN), where the heart beat originates, the expression and functional activity of IP 3 Rs have not been investigated. Objectives:To determine whether SAN express IP 3 Rs and which isoforms are present. To examine the response of the SAN to IP 3 R agonists and antagonist, and the potential role played by IP 3 Rs in cardiac pacemaking. Methods and Results:The expression and distribution of IP 3 Rs were studied by reverse-transcription polymerase chain reaction, Western blotting, and immunolabeling. Ca 2؉ signaling and electric activity in intact mouse SAN were measured with Ca 2؉ -sensitive fluorescent dyes. We found that although the entire SAN expressed three IP 3 R mRNA isoforms, the type II IP 3 R (IP 3 R2) was the predominant protein isoform detected by Western blot using protein extracts from the SAN, atrioventricular node, and atrial tissue. Immunohistochemistry studies also showed that IP 3 R2 was expressed in the central SAN region. Studies using isolated single pacemaker cells revealed that IP 3 R2 (but not IP 3 R1) was located with a similar distribution to the sarcoplasmic reticulum marker protein SERCA2a with some labeling adjacent to the surface membrane. The application of membranepermeable IP 3 (IP 3 -butyryloxymethyl ester) increased Ca 2؉ spark frequency and the pacemaker firing rate in single isolated pacemaker cells. In intact SAN preparations, IP 3 R agonists, endothelin-1 and IP 3 -butyryloxymethyl ester both increased intracellular Ca 2؉ and the pacemaker firing rate, whereas the IP 3 R antagonist, 2-aminoethoxydiphenyl borate decreased Ca 2؉ and the firing rate. Both of these effects were absent in the SAN from transgenic IP 3 R2 knockout mice. Key Words: pacemaker activity Ⅲ sinoatrial node F or many years cardiac pacemaker activity was believed to be determined solely by the electric activity of voltage-dependent membrane currents, particularly the hyperpolarization-activated cation current (I f ). 1 However, the discovery that ryanodine, an antagonist of sarcoplasmic reticulum (SR) Ca 2ϩ release channels (ryanodine receptors), slows the heart rate 2-6 suggested that Ca 2ϩ release from the SR also plays an important role in determining the heart rate. [7][8][9][10][11] Although ryanodine receptors (RyRs) are the main source of SR Ca 2ϩ release, another class of Ca 2ϩ release channels, inositol 1,4,5-trisphosphate receptors (IP 3 Rs), have been found in cardiac SR membranes. 12-14 Although the expression level of IP 3 Rs is much lower than RyRs, Ca 2ϩ release from IP 3 Rs modulates the excitation-contraction coupling in both atrial and ventricular myocytes, 15,16 and several lines of evidence suggest that arrhythmogenic activity in the atria may be associated with increased IP 3 and IP 3 R expression. [17][18][19][20] In addition, new important roles for IP 3 Rs in controlling nuclear transcription ...
Atrial fibrillation (AF) is a significant contributor to cardiovascular morbidity and mortality. The currently available treatments are limited and AF continues to be a major clinical challenge. Clinical studies have shown that AF is frequently associated with dysfunction in the sino-atrial node (SAN). The association between AF and SAN dysfunction is probably related to the communication between the SAN and the surrounding atrial cells that form the SAN-atrial pacemaker complex and/or pathological processes that affect both the SAN and atrial simultaneously. Recent evidence suggests that Ca2+ entry through TRPC3 (Transient Receptor Potential Canonical-3) channels may underlie several pathophysiological conditions -including cardiac arrhythmias. However, it is still not known if atrial and sinoatrial node cells are also involved. In this article we will first briefly review TRPC3 and IP3R signaling that relate to store/receptor-operated Ca2+ entry (SOCE/ROCE) mechanisms and cardiac arrhythmias. We will then present some of our recent research progress in this field. Our experiments results suggest that pacing-induced AF in angiotensin II (Ang II) treated mice are significantly reduced in mice lacking the TRPC3 gene (TRPC3−/− mice) compared to wild type controls. We also show that pacemaker cells express TRPC3 and several other molecular components related to SOCE/ROCE signaling, including STIM1 and IP3R. Activation of G-protein coupled receptors (GPCRs) signaling that is able to modulate SOCE/ROCE and Ang II induced Ca2+ homeostasis changes in sinoatrial complex being linked to TRPC3. The results provide new evidence that TRPC3 may play a role in sinoatrial and atrial arrhythmias that are caused by GPCRs activation.
g While adipogenesis is controlled by a cascade of transcription factors, the global gene expression profiles in the early phase of adipogenesis are not well defined. Using microarray analysis of gene expression in 3T3-L1 cells, we have identified evidence for the activity of 2,568 genes during the early phase of adipocyte differentiation. One of these, the ISL1 gene, was of interest since its expression was markedly upregulated 1 h after initiation of differentiation, with a subsequent rapid decline. Overexpression of ISL1 at early times during adipocyte differentiation but not at later times was found to profoundly inhibit differentiation. This was accompanied by moderate downregulation of peroxisome proliferator-activated receptor ␥ (PPAR␥) levels, substantial downregulation of PPAR␥ downstream genes, and downregulation of bone morphogenetic protein 4 (BMP4) levels in preadipocytes. Readdition of BMP4 overcame the inhibitory effect of ISL1 on the expression of PPAR␥ but not aP2, a gene downstream of PPAR␥, and BMP4 also partially rescued ISL1 inhibition of adipogenesis, an effect which is additive with rosiglitazone. These results suggest that ISL1 is intimately involved in early regulation of adipogenesis, modulating PPAR␥ expression and activity via BMP4-dependent and -independent mechanisms. Our time course gene expression survey sets the stage for further studies to explore other early and immediate regulators.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.