Antagonism by hemoglobin of effects induced by L-arginine in neuromuscular preparations from rats

Abstract

Nitric oxide (NO)-synthase is present in diaphragm, phrenic nerve and vascular smooth muscle. It has been shown that the NO precursor Larginine (L-Arg) at the presynaptic level increases the amplitude of muscular contraction (AMC) and induces tetanic fade when the muscle is indirectly stimulated at low and high frequencies, respectively. However, the precursor in muscle reduces AMC and maximal tetanic fade when the preparations are stimulated directly. In the present study the importance of NO synthesized in different tissues for the L-Arg-induced neuromuscular effects was investigated. Hemoglobin (50 nM) did not produce any neuromuscular effect, but antagonized the increase in AMC and tetanic fade induced by L-Arg (9.4 mM) in rat phrenic nerve-diaphragm preparations. D-Arg (9.4 mM) did not produce any effect when preparations were stimulated indirectly at low or high frequency. Hemoglobin did not inhibit the decrease of AMC or the reduction in maximal tetanic tension induced by L-Arg in preparations previously paralyzed with d-tubocurarine and directly stimulated. Since only the presynaptic effects induced by L-Arg were antagonized by hemoglobin, the present results suggest that NO synthesized in muscle acts on nerve and skeletal muscle. Nevertheless, NO produced in nerve and vascular smooth muscle does not seem to act on skeletal muscle. Key wordsNitric oxide (NO) is generated from Larginine by NO-synthase (1-3). Neuronal NOsynthase is present in the sarcolemma of type II skeletal muscle fibers (4) and in the motor nerve of rats (5). It has been shown that the addition of the NO precursor L-arginine (4.7-9.4 mM) to rat neuromuscular preparations increases the amplitude of muscular contraction (AMC) in preparations indirectly stimulated at 0.2 Hz (6). In contrast, L-arginine (4.7-9.4 mM) reduces AMC when preparations previously paralyzed with d-tubocurarine are directly stimulated at low frequency (7). The facilitatory and inhibitory effects of L-arginine depend on its metabolism to NO, with actions at the pre-and postsynaptic level, respectively (7). Studies conducted at high frequencies of stimulation applied to the motor nerve have shown that L-arginine (4.7-18.4 mM) produces a dose- C.R. Ambiel and Wilson Alves-Do-Prado dependent tetanic fade followed by reduction in maximal tetanic tension (6). The tetanic fade and the reduction in maximal tetanic tension induced by L-arginine are produced by the action of NO on the motor nerve and skeletal muscle, respectively (6).The presynaptic effects observed with Larginine reach their maximum at concentrations around 9.4 mM (6,7). Hemoglobin may cross the wall of a large vein (8), but its diffusion through the membranes of other tissues is negligible (9). NO (authentic gas) disappears rapidly when hemoglobin is added to the bath (10), at a rate proportional to hemoglobin concentration in the bath (10). Since hemoglobin only scavenges NO released from tissues, the pre-and postsynaptic neuromuscular effects induced by NO released from skeletal muscle, motor ner...

The theaflavin fraction is responsible for the facilitatory effect of black tea at the skeletal myoneural junction

“…It was found that L-arginine, but not D-arginine, produced facilitation of neurotransmission at 5 Hz and fade of transmission at 50 Hz and that N G -nitro-L-arginine (NOARG) antagonized both the facilitatory and inhibitory effects of L-arginine which suggested that NO may modulate the release of ACh from the motor nerve terminals (Queiroz and Alves-Do-Prado, 2001). Since the role of calcium (Endo, 1985) and NO (Ambiel and Alves-Do-Prado, 2001;Queiroz and Alves-Do-Prado, 2001) in the neuromuscular transmission has already been established, the possible involvement of calcium and NO in the mode of action of the active principle of black tea on rat diaphragm was also investigated in the study.…”

The Effect of Nitric Oxide on the Rat Diaphragm at Different Frequencies of Indirect Electrical Stimulation

“…Moreover, Wang et al in 1995 noticed that c.GMP-dependent kinase phosphorylate the nicotinic acetylcholine receptor subunits in cultured myocytes. 16,17,18 .…”

Gasotransmitters: Physiology and Pathophysiology

“…The inhibitory action of SIN-1 was prevented by the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) suggesting that NO triggered activation of sGC thereby raising cGMP levels followed by a depression of transmitter release (Barroso et al 2007). In previous studies L-arginine was used at concentrations of 4.7-9.4 mM and increased the amplitude of muscle contraction in preparations indirectly stimulated at 0.2 Hz (Ambiel and Alves-Do-Prado 2001). The NO scavenger, hemoglobin, abolished inhibition of [ 3 H]ACh release caused by SIN-1, but not that caused by L-arginine, suggesting that L-arginine-induced NO formation catalyzed by NOS occurs mainly inside nerve terminals.…”