Tyrosine phosphorylation in contraction of opossum esophageal longitudinal muscle in response to SNP

Pacemaker frequency is increased by sodium nitroprusside in the guinea pig gastric antrum

In the guinea pig gastric antrum, the effects of sodium nitroprusside (SNP), an NO donor, on pacemaker potentials were investigated in the presence of nifedipine. The pacemaker potentials consisted of primary and plateau components; SNP (> 1 microM) increased the frequency of occurrence of these pacemaker potentials, while inhibiting the plateau component. 1H-[1,2,4]-Oxadiazole [4,3-a] quinoxalin-1-one, an inhibitor of guanylate cyclase, had no effect on the excitatory actions of SNP on the frequency of pacemaker potentials. Other types of NO donor, (+/-)-S-nitroso-N-acetylpenicillamine, 3-morpholino-sydnonimine and 8-bromoguanosine 3'5'-cyclic monophosphate had no excitatory effect on pacemaker activity. Forskolin, an activator of adenylate cyclase, or 4,4'-diisothiocyano-stilbene-2,2'-disulphonic acid, an inhibitor of the Ca(2+)-activated Cl(-) channel, strongly attenuated the generation of pacemaker potentials, and SNP added in the presence of these chemicals restored the generation of pacemaker potentials. The pacemaker potentials evoked by SNP were abolished in low-Ca(2+) solution or by membrane depolarization with high-K(+) solution. The SNP-induced generation of pacemaker potentials was not prevented by cyclopiazonic acid, an inhibitor of internal Ca(2+)-ATPase, but was limited to a transient burst by iodoacetic acid, an inhibitor of glycolysis, carbonyl cyanide m-chlorophenyl-hydrazone, a mitochondrial protonophore, or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester, an intracellular Ca(2+) chelator. These results suggest that the SNP-induced increase in the frequency of pacemaker potentials is related to the elevated intracellular Ca(2+) concentrations due to release from mitochondria, and these actions may be independent of the activation of guanylate cyclase.

Role of pp60(c-src) and p(44/42) MAPK in ANG II-induced contraction of rat tonic gastrointestinal smooth muscles

We examined the role of mitogen-activated protein kinase (p(44/42) MAPK) in ANG II-induced contraction of lower esophageal sphincter (LES) and internal anal sphincter (IAS) smooth muscles. Studies were performed in the isolated smooth muscles and cells (SMC). ANG II-induced changes in the levels of phosphorylation of different signal transduction and effector proteins were determined before and after selective inhibitors. ANG II-induced contraction of the rat LES and IAS SMC was inhibited by genistein, PD-98059 [a specific inhibitor of MAPK kinases (MEK 1/2)], herbimycin A (a pp60(c-src) inhibitor), and antibodies to pp60(c-src) and p(120) ras GTPase-activating protein (p(120) rasGAP). ANG II-induced contraction of the tonic smooth muscles was accompanied by an increase in tyrosine phosphorylation of p(120) rasGAP. These were attenuated by genistein but not by PD-98059. ANG II-induced increase in phosphorylations of p(44/42) MAPKs and caldesmon was attenuated by both genistein and PD-98059. We conclude that pp60(c-src) and p(44/42) MAPKs play an important role in ANG II-induced contraction of LES and IAS smooth muscles.

Nitric oxide contracts longitudinal smooth muscle of opossum oesophagus via excitation-contraction coupling

1. The effects of sodium nitroprusside (SNP) and diethylenetriamine/nitric oxide adduct (DETA/NO), putative nitric oxide (NO) donors, on opossum oesophageal longitudinal smooth muscle were investigated using isometric tension and intracellular micro-electrode recordings. 2. SNP produced concentration-dependent contractions of oesophageal longitudinal smooth muscle with an EC(50) of 239.6 +/- 78.2 microM (mean +/- S.E.M., n = 10). Maximal contraction induced by SNP (1 mM) was about 75.5 +/- 8.5 % (n = 10) of the 60 mM KCl-induced contraction. The SNP-induced contraction was resistant to tetrodotoxin (TTX; 1 microM), but abolished by nifedipine (1 microM), as well as by niflumic acid (300 microM) and 9-anthroic acid (9-AC; 1 mM), Ca(2+)-activated Cl(-) channel blockers. 3. DETA/NO at concentrations of 100 and 500 microM induced 83.1 +/- 24.4 and 104.1 +/- 34.9 % of the 60 mM KCl-induced contraction (n = 4), respectively, which was abolished by nifedipine (1 microM), niflumic acid (300 microM) and 9-AC (1 mM). 4. Pre-application of 1H-[1,2,4]oxidiazolo[4,3,-alpha]quinoxalin-1-one (ODQ) (10 microM), a guanylate cyclase inhibitor, significantly inhibited the SNP-induced contraction, whereas 8-bromo-cGMP (1 mM), a membrane-permeable analogue of cGMP, mimicked the SNP-induced contraction. 5. Intracellular recordings revealed that SNP (300 microM) depolarized resting membrane potentials (RMPs) and increased the frequency of spontaneous spike-like action potentials. However, these electrical alterations were eliminated by pretreatment with niflumic acid (300 microM). 6. These results suggest that NO produces an excitation-contraction coupling in opossum oesophageal longitudinal smooth muscle via a cGMP-dependent signalling pathway. This contraction depends on extracellular Ca(2+) entry through activation of L-type Ca(2+) channels.

A redox-based mechanism for the contractile and relaxing effects of NO in the guinea-pig gall bladder

The purpose of this study was to determine the effects of sodium nitroprusside (SNP), 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (DETA/NO) and 3-morpholinosydnonimine (SIN-1), NO donors which yield different NO reactive species (NO+, NO* and peroxynitrite, respectively), as well as exogenous peroxynitrite, on gall bladder contractility. Under resting tone conditions, SNP induced a dose-dependent contraction with a maximal effect (10.3 +/- 0.7 mN, S.E.M.) at 1 mM. Consistent with these findings, SNP caused a concentration-dependent depolarization of gall bladder smooth muscle. The excitatory effects of SNP were dependent on extracellular calcium entry through L-type Ca2+ channels. Furthermore, the contraction and depolarization were sensitive to tyrosine kinase blockade, and an associated increase in tyrosine phosphorylation was detected in Western blot studies. DETA/NO induced dose-dependent relaxing effects. These relaxations were sensitive to the guanylyl cyclase inhibitor 1H-[1,2,4]oxidiazolo[4,3-a]quinoxaline-1-one (ODQ, 2 microM) but they were not altered by treatment with the potassium channel blockers tetraethylammoniun (TEA, 5 mM) and 4-aminopyridine (4-AP, 5 mM). When tested in a reducing environment (created by 2.5 mM 1,4-dithiothreitol, DTT), SNP caused a relaxation of gall bladder muscle strips. Similarly, the SNP-induced contraction was converted to a relaxation, and associated hyperpolarization, when DTT was added during the steady state of an SNP-induced response. SIN-1 (0.1 mM), which has been shown to release peroxynitrite, induced relaxing effects that were enhanced by superoxide dismutase (SOD, 50 U ml(-1)). The relaxations induced by either SIN-1 alone or SIN-1 in the presence of SOD were strengthened by catalase (1000 U ml(-1)) and abolished by ODQ pretreatment. However, exogenous peroxynitrite induced a concentration-dependent contraction, which was dependent on activation of leukotriene (LT) metabolism and extracellular calcium. The peroxynitrite-induced contraction was abolished in the presence of the peroxynitrite scavenger melatonin. These results suggest that SIN-1 behaves as an NO* rather than a peroxynitrite source. We conclude that, depending on the redox state, NO has opposing effects on the motility of the gall bladder, being a relaxing agent when in NO * form and a contracting agent when in NO+ or peroxynitrite redox species form. Knowledge of the contrasting effects of the different redox forms of NO can clarify our understanding of the effects of NO donors on gall bladder and other smooth muscle cell types.