Alteration by lipopolysaccharide of the relationship between intracellular calcium levels and contraction in rat mesenteric artery

Abstract

1 The aim of this work was to investigate the effect of lipopolysaccharide (LPS) treatment on the relationship between the cytosolic Ca2+ ion concentration ([Ca2]i) and contraction in rat resistance arteries, and the involvement of the L-arginine-nitric oxide (NO)-guanosine 3'-5' cyclic monophosphate (cyclic GMP) pathway in these effects. 2 [Ca2+]i and tension were simultaneously recorded in small mesenteric arteries removed from rats 4 h after intraperitoneal injection of E. coUi LPS (30 mg kg-') or solvent. Cyclic GMP was assayed in vessels submitted to identical treatments.3 Basal [Ca21], was higher in vessels from LPS-treated rats compared to controls. LPS did not modify the concentration-contraction curve of noradrenaline. However, the increase in basal [Ca2+], produced by LPS resulted in a shift of the noradrenaline [Ca2+]i-contraction curve to higher [Ca2+], concentrations.4 L-Arginine (300 gM) relaxed noradrenaline (10 gM) pre-contracted arteries from LPS-treated but not from control rats. This effect of L-arginine was reversed by two inhibitors of NO synthase: Nw-nitro-Larginine-methyl-ester (L-NAME, 1 mM) and S-methyl-isothiourea (SMT, 0.1 mM). Both the relaxing effect of L-arginine and its reversal by L-NAME or SMT occurred without any change in [Ca21],.5 LPS treatment did not modify the cyclic GMP content of the small mesenteric arteries. In arteries removed from LPS-treated rats but not from controls, addition of L-arginine (300 gM) was associated with a significant increase in cyclic GMP content, an effect which was prevented by both L-NAME (1 mM) and SMT (0.1 mM). 6 L-NAME (1 mM) produced a greater reduction in cyclic GMP content than SMT (0.1 mM) in control vessels exposed to L-arginine (300 giM). Under the same conditions, SMT produced a larger decrease in cyclic GMP level than L-NAME in arteries taken from LPS-treated rats, consistent with selective inhibition by SMT of the inducible NO-synthase after LPS. 7 These results show that LPS produced two effects in small mesenteric arteries: (i) alterations in Ca21 handling and a decreased sensitivity of myofflaments to Ca2 , (ii) induction of NO-synthase activity resulting in exogenous L-arginine-dependent production of NO and cyclic GMP accumulation. Both effects are likely to be involved in the hyporeactivity induced by LPS in resistance arteries. Keywords: Calcium; endotoxin shock; resistance arteries Introduction Lipopolysaccharide (LPS)-administration decreases vascular resistance, produces vascular hyporeactivity to different vasoconstrictors and promotes the overproduction of nitric oxide (NO) through activation of the inducible isoform of NO synthase (iNOS) (see Stoclet et al., 1993). The effect of LPS on vascular reactivity and the involvement of NO in this effect have been well documented in large conductance arteries such as the aorta (Julou-Schaeffer et al., 1990). However, the sensitivity to noradrenaline was only slightly decreased in the femoral artery (Schneider et al., 1994) and was not significantly impaired in small mesenteric ...

Effects of in Vivo Lipopolysaccharide Infusion on Vasoconstrictor Function of Rat Isolated Mesentery, Kidney, and Aorta

“…Ca 2ϩ measurements in the mesenteric artery were restricted to 24 h, since that was the time when significant changes in contractile responses were observed. The results showed a tendency for smaller changes in Ca 2ϩ after LPS treatment, but these were not significant, so it would appear that, as shown by Martinez et al (1996), a failure to release Ca 2ϩ does not underlie hypocontractility to methoxamine. In the aortae, preparations taken at 24 h after LPS treatment also showed normal responses to caffeine, indicating that a change in mobilization of intracellular Ca 2ϩ also does not underlie hypocontractility to methoxamine, pointing to changes in Ca 2ϩ sensitization of contractile proteins (which can take place without large changes in Ca 2ϩ ) or to the involvement of another factor.…”

“…In contrast, the renal vasoconstrictor response to methoxamine in vivo was not suppressed (Waller et al, 1994). Interestingly, mesenteric bed preparations taken from animals infused with LPS and investigated in vitro did not show reduced vasoconstrictor effects of methoxamine (Tarpey and Randall, 1998), but this may have been due to the mode of administration, since others who have investigated mesenteric arteries isolated from LPS-treated animals have noted an impairment in the sustained contractile response, even though the initial response to agonist exposure was normal (Martinez et al, 1996;Mitolo-Chieppa et al, 1996). The in vitro contractile responsiveness of the renal vasculature in this model of endotoxemia has not been investigated to date.…”

“…waning of the contractile response to noradrenaline in the mesenteric arterial bed (Mitolo-Chieppa et al, 1996) and mesenteric resistance arteries (Martinez et al, 1996) isolated from rats treated with LPS.…”

“…Thus, this indicates that there may be an impairment of Ca 2ϩ release from internal stores at 2 h, but not at 24 h, after LPS infusion. Previous studies have shown elevated basal levels of intracellular Ca 2ϩ in rat aorta caused by sepsis or endotoxin treatment, which may result from an impairment of Ca 2ϩ storage in intracellular organelles (Song et al, 1993;Martinez et al, 1996). Impaired storage, and by implication, release of Ca 2ϩ in intracellular organelles could explain the decreased response to caffeine observed at 2 h. Inducible NOS activity in the aorta in this model of endotoxemia has been shown to increase between 2 and 6 h, and then to be undetectable at 24 h, after the onset of LPS infusion (Gardiner et al, 1995), which is in some respects similar to the temporal change in the response to caffeine.…”

Voltage-independent calcium channels mediate lipopolysaccharide-induced hyporeactivity to endothelin-1 in the rat aorta

“…NS, not statistically significant (P Ͼ 0.05). (26). Since removal of external Ca 2ϩ abolishes this difference in basal [Ca 2ϩ ] i levels, it is unlikely to result from an impairment of [Ca 2ϩ ] i storage (7,15), but probably from enhanced Ca 2ϩ influx through VOCCs (40) or other Ca 2ϩ channels.…”