title: Elevated InsP3R expression underlies enhanced calcium fluxes and spontaneous extra-systolic calcium release events in hypertrophic cardiac myocytes.
abstract: Cardiac hypertrophy is associated with profound remodeling of Ca(2+) signaling pathways. During the early, compensated stages of hypertrophy, Ca(2+) fluxes may be enhanced to facilitate greater contraction, whereas as the hypertrophic heart decompensates, Ca(2+) homeostatic mechanisms are dysregulated leading to decreased contractility, arrhythmia and death. Although ryanodine receptor Ca(2+) release channels (RyR) on the sarcoplasmic reticulum (SR) intracellular Ca(2+) store are primarily responsible for the Ca(2+) flux that induces myocyte contraction, a role for Ca(2+) release via the inositol 1,4,5-trisphosphate receptor (InsP(3)R) in cardiac physiology has also emerged. Specifically, InsP(3)-induced Ca(2+) signals generated following myocyte stimulation with an InsP(3)-generating agonist (e.g., endothelin, ET-1), lead to modulation of Ca(2+) signals associated with excitation-contraction coupling (ECC) and the induction of spontaneous Ca(2+) release events that cause cellular arrhythmia. Using myocytes from spontaneously hypertensive rats (SHR), we recently reported that expression of the type 2 InsP(3)R (InsP(3)R2) is significantly increased during hypertrophy. Notably, this increased expression was restricted to the junctional SR in close proximity to RyRs. There, enhanced Ca(2+) release via InsP(3)Rs serves to sensitize neighboring RyRs causing an augmentation of Ca(2+) fluxes during ECC as well as an increase in non-triggered Ca(2+) release events. Although the sensitization of RyRs may be a beneficial consequence of elevated InsP(3)R expression during hypertrophy, the spontaneous Ca(2+) release events are potentially of pathological significance giving rise to cardiac arrhythmia. InsP(3)R2 expression was also increased in hypertrophic hearts from patients with ischemic dilated cardiomyopathy and aortically-banded mice demonstrating that increased InsP(3)R expression may be a general phenomenon that underlies Ca(2+) changes during hypertrophy.
authors.affiliation: Department of Molecular Signaling, Babraham Institute, Cambridge, UK.
authors.forename: Dagmar
authors.initials: D
authors.lastname: Harzheim
authors.forename: Amarnath
authors.initials: A
authors.lastname: Talasila
authors.forename: Mehregan
authors.initials: M
authors.lastname: Movassagh
authors.forename: Roger S-Y
authors.initials: RS
authors.lastname: Foo
authors.forename: Nichola
authors.initials: N
authors.lastname: Figg
authors.forename: Martin D
authors.initials: MD
authors.lastname: Bootman
authors.forename: H Llewelyn
authors.initials: HL
authors.lastname: Roderick
mesh_terms: D000328:Adult; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D015153:Blotting, Western; D020013:Calcium Signaling; D009202:Cardiomyopathies / Q000209:etiology / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D019332:Endothelin-1 / Q000378:metabolism; D006801:Humans; D006973:Hypertension / Q000150:complications / Q000378:metabolism; D007150:Immunohistochemistry; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000378:metabolism*; D008297:Male; D051379:Mice; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D044022:Receptor, Endothelin A / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D019332:Endothelin-1; D053496:Inositol 1,4,5-Trisphosphate Receptors; D044022:Receptor, Endothelin A; D019837:Ryanodine Receptor Calcium Release Channel