VASCULAR KATP CHANNELS REDUCE SEVERE MUSCLE O2-DELIVERY TO O2-UTILIZATION MISMATCH DURING CONTRACTIONS IN CHRONIC HEART FAILURE RATS

Alexander J. Fees1, Clark T. Holdsworth1, Scott K. Ferguson1, Trenton D. Colburn1, David C. Poole1,2, & Timothy I. Musch1,2 1Department of Anatomy and Physiology, 2Department of Kinesiology, Kansas State University, Manhattan, KS, 66506, USA The vascular ATP-sensitive K+ (KATP) channel is a regulator of skeletal muscle microvascular O2 pressure (PO2mv; set by the O2-delivery to O2-utilization ratio) during contractions. Inadequate tissue PO2mv during exercise in chronic heart failure (CHF) constrains exercise capacity and may be exaggerated by KATP channel inhibition. PURPOSE: We tested the hypotheses that 1) KATP channel inhibition via glibenclamide (GLI), often prescribed for hyperglycemic CHF patients, would augment the PO2mv undershoot, increase the time to reach the steady-state PO2mv and decrease the mean PO2mv during contractions of the spinotrapezius muscle in CHF rats and 2) these effects would be reversed by the administration of pinacidil (PIN, KATP channel activator). METHODS: Muscle PO2mv was measured via the phosphorescence quenching technique during 180s of 1-Hz twitch contractions (~6 V) under control, GLI (5 mg/kg), and PIN (5 mg/kg) conditions in 16 male Sprague-Dawley rats with CHF induced via myocardial infarction (left main coronary artery ligation). RESULTS: GLI augmented the PO2mv undershoot (control: 2.3 ± 0.4, GLI: 4.1 ± 0.5 mmHg, p\u3c0.05) and time-to-reach contracting steady state (control: 66.1 ± 10.2, GLI: 93.6 ± 7.8 s, p\u3c0.05), and reduced baseline (control: 28.3 ± 0.9, GLI: 24.8 ± 1.0 mmHg, p\u3c0.05) and mean PO2mv (control: 20.6 ± 0.6, GLI: 17.6 ± 0.3 mmHg, p\u3c0.05). PIN reversed these effects of GLI (p\u3c0.05 for all) indicating that the primary effects of GLI were KATP channel specific. CONCLUSIONS: KATP channels protect against severe mismatch of muscle O2-delivery to O2-utilization during contractions in CHF rats. These data suggest that sulphonylurea therapy (e.g. GLI) poses an additional constraint to muscle O2 delivery in CHF patients and may further compromise physical activity; a contributing factor to morbidity and mortality

Skeletal Muscle Vascular Control during Exercise: Impact of Nitrite Infusion During Nitric Oxide Synthase Inhibition in Healthy Rats

This is the author accepted manuscript. The final version is available from Sage via the DOI in this recordThe nitric oxide synthase (NOS)-independent pathway of nitric oxide (NO) production in which nitrite (NO2 (-)) is reduced to NO may have therapeutic applications for those with cardiovascular diseases in which the NOS pathway is downregulated. We tested the hypothesis that NO2 (-) infusion would reduce mean arterial pressure (MAP) and increase skeletal muscle blood flow (BF) and vascular conductance (VC) during exercise in the face of NOS blockade via L-NAME. Following infusion of L-NAME (10 mg kg(-1), L-NAME), male Sprague-Dawley rats (3-6 months, n = 8) exercised without N(G)-nitro-L arginine methyl ester (L-NAME) and after infusion of sodium NO2 (-) (7 mg kg(-1); L-NAME + NO2 (-)). MAP and hindlimb skeletal muscle BF (radiolabeled microsphere infusions) were measured during submaximal treadmill running (20 m min(-1), 5% grade). Across group comparisons were made with a published control data set (n = 11). Relative to L-NAME, NO2 (-) infusion significantly reduced MAP (P < 0.03). The lower MAP in L-NAME+NO2 (-) was not different from healthy control animals (control: 137 ± 3 L-NAME: 157 ± 7, L-NAME + NO2 (-): 136 ± 5 mm Hg). Also, NO2 (-) infusion significantly increased VC when compared to L-NAME (P < 0.03), ultimately negating any significant differences from control animals (control: 0.78 ± 0.05, L-NAME: 0.57 ± 0.03, L-NAME + NO2 (-); 0.69 ± 0.04 mL min(-1) 100 g(-1) mm Hg(-1)) with no apparent fiber-type preferential effect. Overall, hindlimb BF was decreased significantly by L-NAME; however, in L-NAME + NO2 (-), BF improved to a level not significantly different from healthy controls (control: 108 ± 8, L-NAME: 88 ± 3, L-NAME + NO2 (-): 94 ± 6 mL min(-1) 100 g(-1), P = 0.38 L-NAME vs L-NAME + NO2 (-)). Individuals with diseases that impair NOS activity, and thus vascular function, may benefit from a NO2 (-)-based therapy in which NO bioavailability is elevated in an NOS-independent manner.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: These experiments were funded by a Kansas State University SMILE award to TIM, and American Heart Association Midwest Affiliate (10GRNT4350011) and NIH (HL-108328) awards to DCP