inositol-1-4-5-trisphosphate and Acute-Disease

Fine-tuning of the activity of inositol 1,4,5-trisphosphate receptors (IP

Topics: Acute Disease; Animals; Calcium Signaling; Disease Models, Animal; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Ion Channel Gating; Male; Mice; Mice, Inbred C57BL; Pancreatitis; Proteolysis; Rats; Rats, Wistar

Hypoxic pulmonary vasoconstriction is caused by a rise in cytosolic Ca(2+) ([Ca(2+)](cyt)) in pulmonary artery smooth muscle cells (PASMC) via multiple mechanisms. PASMC consist of heterogeneous phenotypes defined by contractility, proliferation, and apoptosis as well as by differences in expression and function of various genes. In rat PASMC, hypoxia-mediated decrease in voltage-gated K(+) (Kv) currents (I(K(V))) and increase in [Ca(2+)](cyt) were not uniformly distributed in all PASMC tested. Acute hypoxia decreased I(K(V)) and increased [Ca(2+)](cyt) in approximately 46% and approximately 53% of PASMC, respectively. Using combined techniques of single-cell RT-PCR and patch clamp, we show here that mRNA expression level of Kv1.5 in hypoxia-sensitive PASMC (in which hypoxia reduced I(K(V))) was much greater than in hypoxia-insensitive cells (in which hypoxia negligibly affected I(K(V))). These results demonstrate that 1) different PASMC express different Kv channel alpha- and beta-subunits, and 2) the sensitivity of a PASMC to acute hypoxia partially depends on the expression level of Kv1.5 channels; hypoxia reduces whole-cell I(K(V)) only in PASMC that express high level of Kv1.5. In addition, the acute hypoxia-mediated changes in [Ca(2+)](cyt) also vary in different PASMC. Hypoxia increases [Ca(2+)](cyt) only in 34% of cells tested, and the different sensitivity of [Ca(2+)](cyt) to hypoxia was not related to the resting [Ca(2+)](cyt). An intrinsic mechanism within each individual cell may be involved in the heterogeneity of hypoxia-mediated effect on [Ca(2+)](cyt) in PASMC. These data suggest that the heterogeneity of PASMC may partially be related to different expression levels and functional sensitivity of Kv channels to hypoxia and to differences in intrinsic mechanisms involved in regulating [Ca(2+)](cyt).

Topics: Acute Disease; Animals; Calcium; Cells, Cultured; Hypoxia; Inositol 1,4,5-Trisphosphate; Kv1.5 Potassium Channel; Membrane Potentials; Muscle, Smooth, Vascular; Potassium; Pulmonary Artery; Rats; Rats, Sprague-Dawley; RNA, Messenger; Vasoconstriction

The role of intracellular calcium in acute thermal nociception was investigated in the mouse hot-plate test. Intracerebroventricular (i.c.v.) administration of TMB-8, a blocker of Ca++ release from intracellular stores, produced hypernociception. By contrast, i.c.v. pretreatment with thapsigargin, a depletor of Ca++ intracellular stores, produced an increase of the mouse pain threshold. Furthermore, non-analgesic doses of thapsigargin prevented the hypernociception produced by TMB-8. In mice undergoing treatment with heparin, an InsP3-receptor antagonist, or ryanodine, a ryanodine receptor (RyR) antagonist, a dose-dependent reduction of the pain threshold was observed. Pretreatment with D-myo inositol, compound which produces InsP3, and 4-chloro-m-cresol, a RyR agonist, induced an antinociceptive effect. The heparin hypernociception was prevented by D-myo inositol, but not by L-myo inositol, used as negative control. In the same experimental conditions, the antinociception induced by D-myo inositol was prevented by a non-hyperalgesic dose of heparin. Similarly, the reduction of pain threshold produced by ryanodine was reversed by non-analgesic doses of 4-chloro-m-cresol, whereas the antinocicpetion induced by 4-chloro-m-cresol was prevented by non-hyperalgesic doses of ryanodine. The pharmacological treatments employed did not produce any behavioral impairment of mice as revealed by the rota-rod and hole-board tests. These results indicate that a variation of intracellular calcium contents at a supraspinal level is involved in the modulation of acute thermal nociception. In particular, the stimulation of both InsP3- and Ry-receptors appears to play an important role in the induction of antinociception in mice, whereas a blockade of these receptors is involved in an hypernociceptive response to acute thermal pain.

Topics: Acute Disease; Animals; Behavior, Animal; Calcium; Calcium Channel Blockers; Calcium-Transporting ATPases; Dose-Response Relationship, Drug; Enzyme Inhibitors; Gallic Acid; Hot Temperature; Hyperalgesia; Injections, Intraventricular; Inositol 1,4,5-Trisphosphate; Male; Mice; Pain; Pain Threshold; Postural Balance; Reaction Time; Ryanodine Receptor Calcium Release Channel; Thapsigargin

The role that second messengers play in pulmonary vasoconstriction is not understood. The purpose of this study was to directly measure inositol phosphates in isolated pulmonary arterial preparations before and during norepinephrine (NE) stimulation and acute hypoxia. Rat main pulmonary arteries were isolated and incubated with myo-[3H]-inositol. After incubation, control tissue was stimulated with 0.5 microM NE or 30 mM KCl. Test preparations were precontracted with 30 mM KCl and then exposed to hypoxia. Samples were homogenized and applied to a high-pressure liquid chromatography column for analysis of inositol phosphates. Results show that inositol trisphosphate (IP3) increases twofold at 5 s following NE stimulation. Thirty micromolars of KCl results in a slight but significant increase in IP3 formation at 5 min following the stimulation. Phentolamine inhibits the KCl-induced increase in IP3 formation, whereas A23187 has no effect on IP3 levels. Hypoxia caused a biphasic contraction in the precontracted isolated rat pulmonary artery. IP3 levels did not change during the hypoxic period. In conclusion, NE causes a rapid increase in IP3 formation consistent with the time course of production of an excitation-contraction coupling second messenger. However, inositol trisphosphate is not involved in the signal transduction pathway leading to pulmonary arterial contraction induced by hypoxia.

Topics: Acute Disease; Animals; Calcimycin; Chromatography, High Pressure Liquid; Hypoxia; Inositol 1,4,5-Trisphosphate; Male; Norepinephrine; Potassium Chloride; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Vasoconstriction

The effects of nebulized platelet-activating factor (PAF) on the pulmonary and cardiovascular systems, and on the platelets present in peripheral blood were investigated in 9 normal individuals and in 6 patients with asthma and 3 individuals with lyso-PAF. The inhalation of PAF caused an acute decrease in specific airway conductance. The circulatory system parameters monitored showed an increase in heart rate while blood pressure decreased in both groups that were studied. The inhalation of PAF led to a significant increase in the differential count of polymorphonuclear leukocytes after 15 min; the count returned to the initial level after 24 h. However, the platelet count remained unchanged. The phosphatidylinositol (PI) turnover and in particular the formation of 1,4,5-inositoltrisphosphate (IP3) in platelets were investigated after PAF inhalation. It also mediated an increase in intracellular free calcium concentration, [Ca2+]i, in response to a second challenge with exogenous PAF. The basal levels of IP3 and [Ca2+]i were significantly greater in the platelets of patients with asthma than in those of normal individuals (p less than 0.01). Platelets that had been isolated from normal and asthmatic subjects had a higher concentration of IP3 and [Ca2+]i in the platelets after an in vitro exposure to PAF. After an inhalation challenge with PAF, the platelets of both the normal individuals and the patients with asthma showed a specific refractoriness to the in vitro exposure to PAF. Perhaps, this is an explanation for the PAF-dependent tachyphylaxis that is commonly observed in both normal and asthmatic individuals.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Acute Disease; Administration, Inhalation; Adolescent; Adult; Asthma; Blood Platelets; Bronchoconstriction; Female; Humans; Inositol 1,4,5-Trisphosphate; Male; Phosphatidylinositols; Platelet Activating Factor; Platelet Count