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Exogenous nitric oxide reduces oxygen consumption of isolated ventricular myocytes less than other forms of guanylate
1Department of Physiology and Biophysics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick 08903-0019, USA.
Abstract:
We tested the hypothesis that increasing cyclic GMP with nitric oxide (NO) would reduce cardiac myocyte metabolism less than other forms of guanylate cyclase stimulation. The steady state O2 consumption (VO2) of a suspension of ventricular myocytes in 2.0 mM Ca2+ isolated from hearts of New Zealand white rabbits was measured in a glass chamber using Clark-type oxygen electrode. The cellular cyclic GMP levels, determined by radioimmunoassay, were increased by (1) adding 3-morpholinosydnonimine (SIN-1, 10(-8)-10(-5) M) and nitroprusside (10(-8)-10(-5) M), NO donors-soluble guanylate cyclase stimulators; (2) carbon monoxide (CO, 1.5 x 10(-8)-1.5 x 10(-6) M), soluble guanylate cyclase stimulator and (3) guanylin (10(-8)-10(-5) M), particulate guanylate cyclase stimulator. The baseline myocyte cyclic GMP level was 86 +/- 13 fmol/10(5) myocytes with a corresponding VO2 of 268 +/- 21 nl O2/min per 10(5) myocytes. An inverse relationship between cellular cyclic GMP levels and VO2 existed in these myocytes. The regression equations for the four treatments were: VO2 = -0.45 x [cyclic GMP] + 294.4, r = 0.94 for SIN-1; VO2 = -1.46 x [cyclic GMP] + 444.7, r = 0.96 for CO; VO2 = -1.25 x [cyclic GMP] + 389.1, r = 0.84 for guanylin and VO2 = -0.55 x [cyclic GMP] + 322.8. r = 0.79 for nitroprusside. The regression lines of the two NO donors were parallel. A similar result was also evident for the regressions of CO and guanylin. However, the slopes of both the SIN-1 and nitroprusside regression line were significantly less steep than that of either the CO or guanylin lines. Therefore, VO2 is reduced less for a similar increase in cyclic GMP with NO donors compared to direct stimulation with CO or guanylin. These results suggest that NO has metabolic effects on myocytes in addition to its stimulatory effects on cellular cyclic GMP.
Insights
Increasing cyclic GMP with nitric oxide (NO) reduced cardiac myocyte metabolism less than other guanylate cyclase stimulators. This suggests NO has additional metabolic effects beyond cyclic GMP elevation.
Area of Science:
- Cardiovascular Physiology
- Cellular Metabolism
- Molecular Signaling
Background:
- Cardiac myocyte metabolism is crucial for heart function and is influenced by intracellular signaling pathways.
- Cyclic guanosine monophosphate (cGMP) is a key second messenger involved in regulating cellular processes, including metabolism.
- Nitric oxide (NO) is a signaling molecule that activates soluble guanylate cyclase (sGC), leading to cGMP production.
Purpose of the Study:
- To test the hypothesis that NO-mediated increases in cGMP have a lesser impact on cardiac myocyte metabolism compared to other methods of stimulating guanylate cyclase.
- To investigate the relationship between cellular cyclic GMP levels and oxygen consumption (VO2) in isolated cardiac myocytes under various stimulation conditions.
Main Methods:
- Isolated ventricular myocytes from New Zealand white rabbits were used to measure steady-state oxygen consumption (VO2) using a Clark-type oxygen electrode.
- Cellular cyclic GMP levels were quantified using radioimmunoassay.
- Myocyte cyclic GMP was increased using NO donors (SIN-1, nitroprusside), carbon monoxide (CO), and guanylin.
Main Results:
- An inverse relationship was observed between cellular cyclic GMP levels and VO2 across all tested conditions.
- NO donors (SIN-1, nitroprusside) resulted in regression lines with significantly less steep slopes compared to CO and guanylin.
- This indicates that for a similar increase in cyclic GMP, NO donors reduced VO2 less than direct stimulation with CO or guanylin.
Conclusions:
- Nitric oxide (NO) reduces cardiac myocyte metabolism to a lesser extent than other guanylate cyclase stimulators for a comparable increase in cyclic GMP.
- These findings suggest that NO exerts metabolic effects on myocytes independent of, or in addition to, its direct stimulatory effects on cellular cyclic GMP.
- Further research is warranted to elucidate the precise mechanisms underlying NO's distinct metabolic actions in cardiac myocytes.