Liver perisinusoidal fat-storing cells (FSC) show morphological and ultrastructural characteristics similar to pericytes regulating local blood flow in other organs. In the present study we have analyzed whether FSC respond to local vasoconstrictors such as thrombin, angiotensin-II, and endothelin-1 with an increase in intracellular free calcium concentration (ICa2I1I) coupled with effective cell contraction. All agonists tested induced a rapid and dose-dependent increase in ICa2`i1 followed by a sustained phase lasting several minutes in confluent monolayers of Fura-2-loaded human FSC. Pharmacological studies performed using different Ca2+ channel blockers indicated that, at least for thrombin and angiotensin-II, the sustained phase is due to the opening of voltage-sensitive membrane Ca2" channels. To analyze the temporal and spatial dynamics of Ca2" release in response to these agonists, we performed experiments on individual Fura-2-loaded human FSC using a dual wavelength, ratiometric video imaging system. The rise inICa2"], was exclusively localized to the cytoplasm, particularly in the branching processes. Increases in ICa2"1, more than fourfold were associated with a simultaneous and transient reduction of cell area indicating reversible cell contraction. Our results indicate that the Ca2"-dependent contraction of human FSC in vitro may reflect a potential role in regulating sinusoidal blood flow in vivo. (J. Clin. Invest. 1992. 90:642-646.)

Exposure to an exogenous source of oxygen radicals may induce major electrophysiological alterations in isolated myocytes, which might be related to changes in specific ionic currents and in level of intracellular calcium. These alterations occur with a time course consistent with the rapid onset of ventricular arrhythmias in reperfused hearts.

1 The effects of y-aminobutyric acid (GABA) and related substances were examined in guinea-pig ileum longitudinal muscle. 2 GABA at doses ranging from 1O-7M to 3 x 10-6M elicited a relaxation while at higher doses (3 x 10-6M_10-4 M), as previously described, it caused a contraction followed by relaxation.3 GABA-induced relaxation was bicuculline-insensitive, was mimicked by (-)-baclofen but not by homotaurine and muscimol. The effect of baclofen was stereospecific. GABA-and (-)-baclofeninduced relaxations were dose-dependent and their ED50 values were similar. A specific crossdesensitization occurred between GABA and (-)-baclofen.4 The bicuculline-insensitive relaxation induced by GABA and (-)-baclofen was prevented by tetrodotoxin and hyoscine but not by phentolamine plus propranolol, naloxone or theophylline. 5 In preparations in which the muscle tone was raised by histamine or prostaglandin F2X, GABA and (-)-baclofen induced relaxation to the same extent as before increasing the tone. If the tone was raised by DMPP, a greater bicuculline-insensitive relaxation occurred. 6 Contraction caused by GABA was bicuculline-sensitive and was mimicked by homotaurine and muscimol. Contraction was dose-dependent and muscimol was about three times more potent than GABA or homotaurine. A specific cross-desensitization occurred between the contractile effects of GABA and those of homotaurine or muscimol. 7 Bicuculline competitively antagonized the contractile effects of GABA, homotaurine and muscimol and gave closely similar pA2 values. The slope of the Schild plot for the above drugs was near 1, confirming the competitive nature of the antagonism.8 The bicuculline-sensitive contraction induced by GABA, homotaurine and muscimol was abolished by tetrodotoxin and was non-competitively antagonized by hyoscine, while it was unaffected by hexamethonium, mepyramine and methysergide. 9 It is concluded that two receptors mediate the GABA effects in guinea-pig ileum: a bicucullinesensitive GABAA receptor, which elicits contraction through an excitatory action on cholinergic post-ganglionic neurones; and a bicuculline-insensitive GABAB receptor which causes relaxation through an inhibitory presynaptic action on cholinergic post-ganglionic neurones. We confirm that GABA, homotaurine and muscimol are GABAA agonists, while GABA and (-)-baclofen are GABAB agonists.

1 Effects of substances which are able to alter brain histamine levels on the nociceptive threshold were investigated in mice and rats by means of tests inducing three different kinds of noxious stimuli: mechanical (paw pressure), chemical (abdominal constriction) and thermal (hot plate). 2 A wide range of i.c.v. doses of histamine 2HCI was studied. Relatively high doses were dosedependently antinociceptive in all three tests: 5-100 ,g per rat in the paw pressure test, 5-50 g per mouse in the abdominal constriction test and 50-1I 00 g per mouse in the hot plate test. Conversely, very low doses were hyperalgesic: 0.5 ftg per rat in the paw pressure test and 0.1-1 g per mouse in the hot plate test. In the abdominal constriction test no hyperalgesic effect was observed. 3 The histamine H3 antagonist, thioperamide maleate, elicited a weak but statistically significant dose-dependent antinociceptive effect by both parenteral (10-40mgkg-') and i. 5 Thioperamide-induced antinociception was completely prevented by pretreatment with a nonhyperalgesic i.p. dose of (R)-a-methylhistamine in the mouse hot plate and abdominal constriction tests. Antagonism was also observed when both substances were administered i.c.v. in rats. 6 L-Histidine HCl dose-dependently induced a slowly occurring antinociception in all three tests. The doses of 250 and 500mgkg-', i.p. were effective in the rat paw pressure test, and those of 500 and 1500mgkg'1, i.p. in the mouse hot plate test. In the mouse abdominal constriction test 500 and 1000mgkg'1, i.p. showed their maximum effect 2h after treatment. 8 To ascertain the mechanism of action of the antinociceptive effect of L-histidine and metoprine, the two substances were also studied in combination with the histamine synthesis inhibitor (S)-a-fluoromethylhistidine and with (R)-o-methylhistamine, respectively. L-Histidine antinociception was completely antagonized in all three tests by pretreatment with (S)-a-fluoromethylhistidine HCl (50 mg kg', i.p.) administered 2 h before L-histidine treatment. Similarly, metoprine antinociception was prevented by (R)-a-methylhistamine dihydrogenomaleate 20 mg kg-', i.p. administered 15 min before metoprine. Both (S)-a-fluoromethylhistidine and (R)-a-methylhistamine were used at doses which did not modify the nociceptive threshold when given alone. 9 The catabolism product, 1-methylhistamine, administered i.c.v. had no effect in either rat paw pressure or mouse abdominal constriction tests.10 These results indicate that the antinociceptive action of histamine may take place on the postsynaptic site, and that its hyperalgesic effect occurs with low doses acting on the presynaptic receptor. This hypothesis is supported by the fact that the H3 antagonist, thioperamide is antinociceptive and the H3 agonist, (R)-a-methylhistamine is hyperalgesic, probably modulating endogenous histamine release. L-Histidine and metoprine, which are both able to increase brain histamine levels, are also able to induce antinociception in mice and rats. Involvement of the histaminer...

1 The effects of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) were evaluated on superoxide anion (0 1) production by guinea-pig alveolar macrophages (AM).2 SP dose-dependently (ED50 = 0.7 nM) evoked 01 production from guinea-pig AM; the N-terminal heptapeptide, SP(1-7), was ineffective. In the presence of thiorphan (10-M), an enkephalinase inhibitor, the stimulating effects of SP were not significantly modified. NKA and NKB were both able to induce 01 production from guinea-pig AM, ED50 values being 0.1 and 1.3 nm, respectively. Therefore, the rank order of activity of natural tachykinins was NKA > SP > NKB. Tachykinin-evoked effects were quantitatively similar to those elicited by the autacoid mediator PAF-acether and less than those induced by the synthetic peptide N-formylmethionyl-leucyl-phenylalanine (FMLP). 3The NK2 receptor agonist [fi-Ala8]-NKA (4-10) dose-dependently evoked 01 production from guinea-pig AM; the NK1 receptor agonist [Pro9]-SP sulphone acted only at high concentrations, while the NK3 receptor agonist [Me,Phe7]-NKB was ineffective. 4 These findings indicate that guinea-pig AM possess NK2 and possibly some NK1 tachykinin receptors and further suggest tachykinin involvement in lung pathophysiology.

1 The ability to modify the pain threshold by the two M,-muscarinic agonists: AF-102B and by the specific M2-agonist arecaidine was examined in mice and rats by using three different noxious stimuli: chemical (writhing test), thermic (hot-plate test) and mechanical (paw pressure test).

Platelet-derived growth factor (PDGF) is a key mitogen for hepatic stellate cells (HSC) and has been shown to be implicated in liver tissue repair and fibrogenesis. In this study the relationship between PDGF-induced intracellular Ca2+ concentration ([Ca2+]i) increase and mitogenesis in cultured human HSC was evaluated. In high-density cell cultures (80-90% subconfluence), PDGF induced a significant increase in [Ca2+]i, characterized by a short-lasting peak phase, which was followed by a long-lasting plateau phase. The plateau phase was abolished in the absence of extracellular Ca2+. However, in low-density cell cultures (30-40% subconfluence), the plateau phase was absent or markedly less pronounced. In parallel sets of experiments, PDGF was significantly less effective in inducing mitogenesis in low-density cell cultures than in high-density cell cultures and was totally ineffective in the absence of extracellular Ca2+. These results suggest that 1) spatial and time dynamics of PDGF-induced [Ca2+]i increase are dependent on cell density and 2) PDGF-induced mitogenesis requires extracellular Ca2+ influx.

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