Role of Nitric Oxide in Neuromuscular Transmission and Its Effects at Different Frequencies of Nerve Stimulation | ||||
| Bulletin of Egyptian Society for Physiological Sciences | ||||
| Article 13, Volume 27, Issue 1, June 2007, Page 185-202 PDF (511.1 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/besps.2007.37134 | ||||
 View on SCiNiTO | ||||
| Authors | ||||
| Mohamed Emran* 1; Hemmat Kholousy1; Samah El-Attar1; Rasha El-Deeb2 | ||||
| 1The Physiology Department, Faculty of Medicine, Cairo University | ||||
| 2The Physiology Department, Faculty of Medicine, MUST | ||||
| Abstract | ||||
| Background:The free radical gas nitric oxide (NO) exhibits diverse vital roles in the human body.It is now recognized as a major messenger molecule. Neural NO-synthase is present in the sarcolemma of type II skeletal muscle fibers. In rats, the NO synthase pathway is present in skeletal muscle, vascular smooth muscle and motor nerve terminal. However, previous studies did not determine whether NO facilitates or impairs neuromuscular transmission in preparations indirectly stimulated at different frequencies. Aim of work: The study aims to examine the effect of NO in rat neuromuscular preparation at different stimulation frequencies and modulation of its effect by hemoglobin (NO scavenger). Methods: 30 rats were used in the experiment and were divided into 2 groups: GpI: rat diaphragms were electrically stimulated by supramaximal stimuli, at low frequency of 0.5Hz for 0.5msec, directly and indirectly to induce simple muscle twitch, GpII: rat diaphragms were electrically stimulated by high frequency of 100Hz, directly and indirectly to induce tetanic contraction. Rat diaphragms were bathed in Krebs solution. To investigate the effect of NO, L-arginine was added to the bath in a dose of 4.7nM/50ml bath. Then bovine Hb (50 nM /50ml bath was added to scavenge NO. A contact time of 3 minutes is allowed for each step and the amplitude of maximal contraction(∆Y), contraction time(∆X), and 1/2 relaxation time (1/2Rt) were measured in GpI, while only amplitude of maximal contraction was measured in GpII. Results: NO significantly increased ∆Y, ∆X and decreased 1/2 Rt when rat diaphragm preparations were stimulated indirectly at low or high frequencies. In contrast, when rat diaphragm preparations were stimulated directly at either low or high frequencies, NO significantly decreased ∆Y, ∆X, and increased 1/2 Rt. Bovine Hb completely reversed the NO effects. Conclusion: We can conclude that NO has dual actions, facilitatory and inhibitory, on skeletal muscle contraction using indirect or direct electrical stimulation respectively at both low and high frequencies. Bovine Hb antagonized the effects of NO in all experimental steps, giving an additional proof that the recorded changes were NO mediated. | ||||
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