Pertussis toxin-sensitive G proteins influence nitric oxide synthase III activity and protein levels in rat heart

Joshua M. Hare, Benjamin Kim, Nicholas A. Flavahan, Kelly M. Ricker, Xinqi Peng, Laurence Colman, Robert G. Weiss, David A. Kass

Research output: Contribution to journalArticle

Abstract

Inhibitory G protein activity (G(i)) and nitric oxide (NO) modulate muscarinic-cholinergic (MC) inhibition of cardiac β-adrenergic inotropic responses. We hypothesized that G(i) mediates MC-NO synthase (NOS) signal transduction. Isoproterenol (0.2-0.8 μg/min) and acetylcholine (1 μM) were administered to isolated perfused rat hearts pretreated with saline (controls; n = 8) or pertussis toxin (PT; 30 μg/kg intraperitoneally 3 d before study; n = 20). PT abrogated in vitro ADP-ribosylation of G(i) protein α subunit(s) indicating near-total decrease in G(i) protein function. Isoproterenol increased peak + dP/dt in both control (peak isoproterenol effect: +2,589 ± 293 mmHg/s, P < 0.0001) and PT hearts (+3,879 ± 474 mmHg/s, P < 0.0001). Acetylcholine reversed isoproterenol inotropy in controls (108 ± 21% reduction of +dP/dt response, P = 0.001), but had no effect in PT hearts. In controls, N(G)-monomethyl-L-arginine (100 μM) reduced basal +dP/dt, augmented isoproterenol +dP/dt (peak effect: +4,634 ± 690 mmHg/s, P < 0.0001), and reduced the MC inhibitory effect to 69 ± 8% (P < 0.03 vs. baseline). L-arginine (100 μM) had no effect in controls but in PT hearts decreased basal +dP/dt by 1,426 ± 456 mmHg/s (P < 0.005), downward-shifted the isoproterenol concentration-effect curve, and produced a small MC inhibitory effect (27 ± 4% reduction, P < 0.05). This enhanced response to NO substrate was associated with increased NOS III protein abundance, and a three- to fivefold increase in in vitro calcium-dependent NOS activity. Neomycin (1 μM) inhibition of phospholipase C did not reverse L-arginine enhancement of MC inhibitory effects. These data support a primary role for G(i) in MC receptor signal transduction with NOS in rat heart, and demonstrate regulatory linkage between G(i) and NOS III protein levels.

Original languageEnglish (US)
Pages (from-to)1424-1431
Number of pages8
JournalJournal of Clinical Investigation
Volume101
Issue number6
DOIs
StatePublished - Mar 15 1998

Keywords

  • L-arginine
  • Muscarinic receptor
  • Myocardial contractility
  • Phospholipase C
  • β-adrenergic receptor

ASJC Scopus subject areas

  • Medicine(all)

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