Effects of L-arginine on the diaphragm muscle twitches elicited at different frequencies of nerve stimulation

Abstract

In rats, the nitric oxide (NO)-synthase pathway is present in skeletal muscle, vascular smooth muscle, and motor nerve terminals. Effects of NO were previously studied in rat neuromuscular preparations receiving low (0.2 Hz) or high (200 Hz) frequencies of stimulation. The latter frequency has always induced tetanic fade. However, in these previous studies we did not determine whether NO facilitates or impairs the neuromuscular transmission in preparations indirectly stimulated at frequencies which facilitate neuromuscular transmission. Thus, the present study was carried out to examine the effects of NO in rat neuromuscular preparations indirectly stimulated at 5 and 50 Hz. The amplitude of muscular contraction observed at the end (B) of a 10-s stimulation was taken as the ratio (R) of that obtained at the start (A) (R = B/A). S-nitroso-N-acetylpenicillamine (200 µM), superoxide dismutase (78 U/ml) and L-arginine (4.7 mM), but not D-arginine (4.7-9.4 mM), produced an increase in R (facilitation of neurotransmission) at 5 Hz. However, reduction in the R value (fade of transmission) was observed at 50 Hz. N G -nitro-L-arginine (8.0 mM) antagonized both the facilitatory and inhibitory effects of L-arginine (4.7 mM). The results suggest that NO may modulate the release of acetylcholine by motor nerve terminals. Key words Nitric oxide (NO) is synthesized by NOsynthase (NOS) (1-3). In the rat, NOS is present in the sarcolemma of type II fibers of skeletal muscle (4), in vascular smooth muscle (5), and in motor nerve terminals (6). Since NOS is a stereospecific enzyme, the effects induced by L-arginine are not observed in the presence of D-arginine under similar experimental conditions (7,8)L-arginine methyl ester; L-arginine ethyl ester, and N G -nitro-L-arginine methyl ester) are used as inhibitors of NOS. The effects produced by endogenous NO (from L-arginine) are pharmacologically similar to those induced by NO released from an exogenous source such as 3-(4-morpholinyl)-syndonone imine (SIN-1) or S-nitroso-N-acetylpenicillamine (SNAP) (9).The amplitude of muscular contraction (AMC) is stable when the diaphragm is indirectly stimulated at 0.2 Hz. A progressive increase in AMC is observed at 5 Hz (see Acting at the presynaptic level, the NO precursor L-arginine (4.7-9.4 mM) produces a dose-dependent increase of AMC in rat neuromuscular preparations indirectly stimulated at 0.2 Hz (10). In contrast, acting on skeletal muscle, it reduces AMC in preparations previously paralyzed with d-tubocurarine and directly stimulated at 0.2 Hz (10). The presynaptic action of NO reduces the effect produced by its postsynaptic action (10). On the other hand, the NO precursor Larginine (4.7 to 9.4 mM) or SIN-1 acting at the presynaptic level produces a dose-dependent increase in tetanic fade when the nerve is stimulated at 200 Hz (11). The same high frequency of stimulation reduces the maximal tetanic tension (postsynaptic action) when applied to the rat phrenic nerve diaphragm preparation previously treated with L-arginine o...

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 .…”

“…In addition, Queiroz and Alves -Do-Prado 2001 suggested that, the increase in the amplitude of muscle contraction produced at different frequencies, depend on the metabolism of L-argnine producing additional NO in the tissues and its ability to scavenge superoxide anions. They reported that NOS activity might change according to the applied frequency of stimulation to the motor nerve 3 . It was also possible that during high-frequency stimulation, presynaptic as well as postsynaptic components are activated through a variety of signal transduction cascades.…”

“…Intracellular NO production is catalyzed by several isoforms of an enzyme termed, nitric oxide synthase (NOS). Neural NOsynthase is present in the sarcolemmma of type II skeletal muscle fibers 3 . In rats, the nitric oxide (NO) synthase pathway is present in skeletal muscle, vascular smooth muscle and motor nerve terminal 3,4 .…”

“…Neural NOsynthase is present in the sarcolemmma of type II skeletal muscle fibers 3 . In rats, the nitric oxide (NO) synthase pathway is present in skeletal muscle, vascular smooth muscle and motor nerve terminal 3,4 . This study aims to investigate the effect of NO in rat neuromuscular preparation (diaphragm) at different frequencies of nerve stimulation and modulation of its effect by hemoglobin as NO scavenger.…”

4-Aminopyridine inhibits the neuromuscular effects of nitric oxide and 8-Br-cGMP

“…In contrast, L-arginine and SIN-1 reduce the maximal tetanic tension (postsynaptic action) when a high stimulation frequency is applied directly to diaphragm preparations previously treated with d-tubocurarine (11). The presynaptic and postsynaptic effects of NO were also observed in assays performed at high frequency with superoxide dismutase, a selective scavenger of superoxide anion radicals (11,12). Since the NO-induced neuromuscular effects may depend on a direct and/or indirect interaction with K + channels, the present study was undertaken to determine the neuromuscular effects of the NO precursor L-arginine and of 8-Br-cGMP on the rat phrenic nerve diaphragm preparation previously treated with a K + channel blocker.…”