title: Nitric oxide effects on shortening velocity and power production in the rat diaphragm.
abstract: The present experiments tested nitric oxide (NO) effects on shortening velocity and power production in maximally activated rat diaphragm. Diaphragm fiber bundles (n = 10/group) were incubated at 37 degrees C in Krebs-Ringer solution containing no added drug (control), the NO synthase inhibitor N omega-nitro-L-arginine (L-NNA; 10 mM), the NO donor sodium nitroprusside (SNP; 1 mM), or a combination (L-NNA + SNP) Loaded shortening velocity was measured via the load-clamp technique over a range of afterloads. Force-velocity data were fitted to the Hill equation to determine maximum velocity of shortening (Vmax). Unloaded shortening velocity was measured in control and L-NNA-treated bundles (n = 12/group) by using the slack test. Maximal isometric force and unloaded shortening velocity were not altered by L-NNA. In contrast, L-NNA decreased maximum velocity of shortening (P < 0.05), loaded shortening velocity (P < 0.0001), and power production (P < 0.0001). All L-NNA effects were prevented by coincubating fiber bundles with L-NNA + SNP. SNP alone had no effect on any variable. These data indicate that endogenous NO is essential for optimal myofilament function during active shortening.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Morrison
authors.forename: C C
authors.initials: CC
authors.lastname: Miller
authors.forename: M B
authors.initials: MB
authors.lastname: Reid
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D003964:Diaphragm / Q000187:drug effects*; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects*; D009569:Nitric Oxide / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D009569:Nitric Oxide; D001120:Arginine