title: Nitroxyl increases force development in rat cardiac muscle.
abstract: Donors of nitroxyl (HNO), the reduced congener of nitric oxide (NO), exert positive cardiac inotropy/lusitropy in vivo and in vitro, due in part to their enhancement of Ca(2+) cycling into and out of the sarcoplasmic reticulum. Here we tested whether the cardiac action of HNO further involves changes in myofilament-calcium interaction. Intact rat trabeculae from the right ventricle were mounted between a force transducer and a motor arm, superfused with Krebs-Henseleit (K-H) solution (pH 7.4, room temperature) and loaded iontophoretically with fura-2 to determine [Ca(2+)](i). Sarcomere length was set at 2.2-2.3 microm. HNO donated by Angeli's salt (AS; Na(2)N(2)O(3)) dose-dependently increased both twitch force and [Ca(2+)](i) transients (from 50 to 1000 microm). Force increased more than [Ca(2+)](i) transients, especially at higher doses (332 +/- 33% versus 221 +/- 27%, P < 0.01 at 1000 microm). AS/HNO (250 microm) increased developed force without changing Ca(2+) transients at any given [Ca(2+)](o) (0.5-2.0 mm). During steady-state activation, AS/HNO (250 microm) increased maximal Ca(2+)-activated force (F(max), 106.8 +/- 4.3 versus 86.7 +/- 4.2 mN mm(-2), n = 7-8, P < 0.01) without affecting Ca(2+) required for 50% activation (Ca(50), 0.44 +/- 0.04 versus 0.52 +/- 0.04 microm, not significant) or the Hill coefficient (4.75 +/- 0.67 versus 5.02 +/- 1.1, not significant). AS/HNO did not alter myofibrillar Mg-ATPase activity, supporting an effect on the myofilaments themselves. The thiol reducing agent dithiothreitol (DTT, 5.0 mm) both prevented and reversed HNO action, confirming AS/HNO redox sensitivity. Lastly, NO (from DEA/NO) did not mimic AS/HNO cardiac effects. Thus, in addition to reported changes in Ca(2+) cycling, HNO also acts as a cardiac Ca(2+) sensitizer, augmenting maximal force without altering actomyosin ATPase activity. This is likely to be due to modulation of myofilament proteins that harbour reactive thiolate groups that are targets of HNO.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, The Johns Hopkins University School of Medicine, Tower 711, 600 N Wolfe Street, Baltimore, MD 21287, USA.
authors.forename: Tieying
authors.initials: T
authors.lastname: Dai
authors.forename: Ye
authors.initials: Y
authors.lastname: Tian
authors.forename: Carlo Gabriele
authors.initials: CG
authors.lastname: Tocchetti
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Katori
authors.forename: Anne M
authors.initials: AM
authors.lastname: Murphy
authors.forename: David A
authors.initials: DA
authors.lastname: Kass
authors.forename: Nazareno
authors.initials: N
authors.lastname: Paolocci
authors.forename: Wei Dong
authors.initials: WD
authors.lastname: Gao
mesh_terms: D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D006321:Heart / Q000502:physiology*; D006834:Hydrazines / Q000494:pharmacology; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism; D009210:Myofibrils / Q000201:enzymology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009573:Nitrites / Q000494:pharmacology; D009589:Nitrogen Oxides / Q000494:pharmacology*; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D006834:Hydrazines; D020030:Nitric Oxide Donors; D009573:Nitrites; D009589:Nitrogen Oxides; C021229:oxyhyponitrite; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; D017301:Ca(2+) Mg(2+)-ATPase; C039900:nitroxyl; D002118:Calcium