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N Nakahata

Publications and source records attributed to N Nakahata.

At least 19 recordsLinked to original sources
PubMed1992

The presence of thromboxane A2 receptors in cultured astrocytes from rabbit brain.

We have previously shown that human astrocytoma cells (1321N1) express thromboxane A2 (TXA2) receptors, of which stimulation activates phosphoinositide hydrolysis (Nakahata et al., Eur. J. Pharmacol. 162 (1989) 407). In order to examine whether TXA2 receptors exist in native astrocytes or not, rabbit cultured astrocytes were used. Glial fibrillary acidic protein (GFAP)-positive astrocytes were obtained three weeks after culture of brain. [3H]ONO NT-126, a TXA2 antagonist, bound to the membranes derived from cultured rabbit astrocytes with the dissociation constant (Kd) of 0.23 nM and the maximum binding site (Bmax) of 69.5 fmol/mg protein. STA2, a stable TXA2 receptor agonist, activates phosphoinositide hydrolysis in a concentration-dependent manner, and S-145, a TXA2 antagonist, inhibited STA2-induced phosphoinositide hydrolysis. The results indicate that TXA2 receptors exist in cultured rabbit astrocytes and the activation of TXA2 receptors results in phosphoinositide hydrolysis.

Animals↗
PubMed1992

Calcium mobilization and its desensitization induced by endothelins and sarafotoxin in human astrocytoma cells (1321N1): comparison of histamine-induced calcium mobilization.

Intracellular free Ca2+ concentration ([Ca2+]i) was monitored in monolayer of 1321 N1 astrocytoma cells by using a fluorescent Ca2+ indicator fura-2. Endothelin-1 (ET-1), endothelin-2 (ET-2), and sarafotoxin Sb6 (SRTX) increased [Ca2+]i from 56 +/- 6 nM to 360 +/- 82, 120 +/- 51, 143 +/- 29 nM, respectively, immediately after their addition to the perfusate with maximum response of more than 0.1 microM of peptides. Endothelin-3 (less than 1 microM) did not affect [Ca2+]i. The increase in [Ca2+]i in response to either ET-1, ET-2, or SRTX could be almost completely inhibited by pretreating cells with ET-1 or ET-2. The homologous desensitization of [Ca2+]i induced by ETs and SRTX is in good agreement with their affinity toward an ETA receptors. The responses in [Ca2+]i by ETs and SRTX were not affected in the desensitized state induced by the pretreatment of histamine in the presence of extracellular Ca2+. However, the response in [Ca2+]i by ETs and SRTX were reduced in the desensitized state induced by pretreatment of histamine in the absence of extracellular Ca2+. These results indicate that depletion of the intracellular Ca2+ stores is responsible for the heterologous desensitization between ETs and histamine.

Calcium↗
PubMed1992

[Signal transduction of prostaglandin E2 and thromboxane A2].

The signal transduction of prostaglandin E2 (PGE2) and thromboxane A2 (TXA2), cyclooxygenase products of arachidonic acid, was investigated in smooth muscle preparations and 1321N1 human astrocytoma cells. While PGE2 has been known to stimulate (via EP2 receptor) or inhibit (via EP3 receptor) adenylate cyclase, PGE2 activated phosphatidylinositol 4,5-bisphosphate (PIP2)-specific phospholipase C (PLase C) in non-vascular smooth muscles (via EP1 receptor), resulting in accumulations of inositol trisphosphate (IP3) and diacylglycerol to elicit intracellular Ca2+ mobilization. On the other hand, STA2, a TXA2 receptor analogue, also accumulated IP3 in human astrocytoma cells. [3H]SQ 29548, a TXA2 receptor antagonist, specifically bound to astrocytoma membranes. TXA2-receptor antagonists (ONO NT-126, S-145, SQ29548 and ONO3708) concentration-dependently inhibited PIP2-specific PLase C activation by STA2, and they also inhibited [3H]SQ 29548 binding in human astrocytoma cells. The Ki value of each antagonist in PIP2-specific PLase C inhibition was similar to that in [3H]SQ29548 binding inhibition. In membrane preparations, STA2 activated PIP2-specific PLase C in the presence of GTP gamma S. Pertussis toxin (IAP) did not affect STA2-induced PLase C activation. The results suggest that stimulation of TXA2 receptors activates PIP2-specific PLase C via an IAP-insensitive G-protein.

Animals↗
PubMed1992

Thromboxane A2 receptor characterization in human astrocytoma cells and rabbit platelets by a new thromboxane antagonist, [3H]ONO NT-126.

Thromboxane A2 receptors of human astrocytoma cells and rabbit platelets were characterized by a binding of a new potent and selective thromboxane A2 antagonist, [3H]ONO NT-126. [3H]ONO NT-126 bound with a high affinity to membranes derived from astrocytoma cells and platelets. In astrocytoma cells, the nonspecific binding determined by 1 microM S-145 was observed in high percentage to total binding. Scatchard plots of both membranes were linear, expressing a single binding site with the Kd of 0.17 nM and Bmax of 46.4 fmol/mg protein in astrocytoma cell membranes and with the Kd of 0.28 nM and Bmax of 1585 fmol/mg protein in platelet membranes, respectively. [3H]ONO NT-126 binding was displaced most potently by ONO NT-126 among other thromboxane A2 analogues. [3H]ONO NT-126 binding was displaced by ONO NT-126, S-145, SQ29548, STA2 and U46619 with Ki values (nM) of 0.21, 1.14, 7.05, 23.5 and 235 in astrocytoma cell membranes and 0.23, 5.55, 259, 9.25 and 43.7 in platelet membranes, respectively. The characteristics of TXA2 receptors apparently differ in rabbit platelets and human astrocytoma cells.

Animals↗
PubMed1991

Trifluoperazine inhibits phosphoinositide hydrolysis as a histamine H1-receptor antagonist.

In human astrocytoma cells (1321N1), trifluoperazine potently inhibited histamine-induced phosphoinositide hydrolysis, while it slightly inhibited carbachol-induced phosphoinositide hydrolysis. Trifluoperazine as well as diphenhydramine inhibited [3H]mepyramine binding in astrocytoma cell membranes with Ki values of 0.052 microM and 0.005 microM, respectively. However, trifluoperazine only slightly inhibited [3H]quinuclidinyl benzilate binding with a Ki value of 3 microM. These results indicate that trifluoperazine specifically inhibits histamine-induced phosphoinositide hydrolysis as a histamine H1-receptor antagonist in human astrocytoma cells.

Astrocytoma↗
PubMed1991

Adenosine inhibits histamine-induced phosphoinositide hydrolysis mediated via pertussis toxin-sensitive G protein in human astrocytoma cells.

The effect of adenosine on phosphoinositide hydrolysis was examined in 1321N1 human astrocytoma cells. Adenosine, L-N6-phenylisopropyladenosine (L-PIA), and 5'-(N-ethylcarboxamido)adenosine (NECA) inhibited histamine-stimulated accumulation of inositol phosphates in a concentration-dependent manner. The potency order of adenosine analogues for inhibition of inositol phosphate accumulation was L-PIA greater than adenosine greater than NECA, a finding indicating that A1-class adenosine receptors are involved in the inhibition. The reduction in inositol phosphate accumulation by L-PIA was blocked by an adenosine receptor antagonist, 8-phenyltheophylline. Stimulation of A1-class adenosine receptors inhibited isoproterenol-stimulated cyclic AMP accumulation as well as histamine-induced inositol phosphate accumulation. Both inhibitory effects were blocked by pretreatment of the cells with pertussis toxin [islet-activating protein (IAP)]. L-PIA also inhibited guanosine 5'-(gamma-thio)triphosphate (GTP gamma S)-stimulated accumulation of inositol phosphates in membrane preparations, and 8-phenyl-theophylline antagonized the inhibition. L-PIA could not inhibit GTP gamma S-induced accumulation of inositol phosphates in IAP-treated membranes. Gi/Go, purified from rabbit brain, inhibited GTP gamma S-stimulated accumulation of inositol phosphates in a concentration-dependent manner in membrane preparations. These results suggest that stimulation of A1-class adenosine receptors interacts with the IAP-sensitive G protein(s), resulting in the inhibitions of phospholipase C as well as adenylate cyclase in human astrocytoma cells.

Adenosine↗
PubMed1990

ONO NT-126 is a potent and selective thromboxane A2 antagonist in human astrocytoma cells.

Stimulation of thromboxane A2 (TXA2) receptors in human astrocytoma cells (1321N1) results in activation of phospholipase C via a pertussis toxin-insensitive G-protein. In the present study, the potency of a new TXA2 receptor antagonist, ONO NT-126, was examined with regard to receptor binding and phosphoinositide hydrolysis in human astrocytoma cells and was compared to that of the other known TXA2 antagonists. [3H]SQ29548 binding to membranes was inhibited by ONO NT-126 and the other TXA2 antagonists with Ki values (nM) of 0.09, 2.18, 8.35 and 25.9 for ONO NT-126, S-145, SQ29548 and ONO3708, respectively. STA2 and U46619, TXA2 receptor agonists, also inhibited [3H]SQ29548 binding with Ki (nM) of 25.1 and 233.5, respectively. STA2 and U46619 stimulated phosphoinositide hydrolysis in a concentration-dependent manner with EC50 values of 43.6 nM for STA2 and 1.2 microM for U46619, respectively. STA2 (1 microM)-induced phosphoinositide hydrolysis was also inhibited by TXA2 antagonists. The Ki values of TXA2 antagonists for the inhibition of phosphoinositide hydrolysis (nM) were 0.10 for ONO NT-126, 3.31 for S-145, 8.31 for SQ29548 and 19.49 for ONO3708 all of which were similar to those for receptor binding. The results indicate that ONO NT-126 is a potent and selective antagonist of TXA2 receptors in human astrocytoma cells.

Astrocytoma↗
PubMed1990

Mastoparan inhibits phosphoinositide hydrolysis via pertussis toxin-insensitive [corrected] G-protein in human astrocytoma cells.

Mastoparan inhibited [3H]inositol phosphate accumulation induced by carbachol as well as cyclic AMP accumulation induced by isoproterenol in 1321N1 human astrocytoma cells. Mastoparan inhibited GTP gamma S-induced, but not Ca2(+)-induced, [3H]inositol phosphate accumulation in membrane preparations with an IC50 of approximately 10 microM. The inhibitory effect of mastoparan on carbachol-induced [3H]inositol phosphate accumulation was resistant to pertussis toxin (IAP) treatment in intact cells. These results suggest that mastoparan inhibits phospholipase C in human astrocytoma cells via a GTP binding protein, which is not a substrate for IAP.

Astrocytoma↗
PubMed1990

PGJ2 and delta 12PGJ2 inhibit cell growth accompanied with inhibition of phosphoinositide turnover in human astrocytoma cells.

PGJ2 and delta 12PGJ2 (1 microM to 30 microM) inhibited the growth of human astrocytoma cells (1321N1) in a time-dependent manner within 48 hrs, determined by [3H]thymidine incorporation into acid-insoluble fraction or amounts of protein. The EC50 values for PGJ2 and delta 12PGJ2 were approximately 8 microM and 6 microM, respectively. [3H]Thymidine incorporation to acid insoluble fraction was inhibited by these PGs within 1 hr, indicating that these PGs rapidly affect cell functions. Although it has been reported that an increase in cyclic AMP inhibits cell growth, PGJ2 and delta 12PGJ2, but not PGE1, reduced isoproterenol (10 microM)-induced accumulation of cyclic AMP, suggesting that PGJ2 and delta 12PGJ2 may disturb adenylate cyclase system, which might be independent on cell growth. On the other hand, these PGs inhibited the incorporation of [3H]inositol into phospholipid fraction within 6 hrs. Furthermore, PGJ2 and delta 12PGJ2 inhibited carbachol- and/or histamine-induced accumulation of inositol phosphates with a similar dose-dependency to their inhibitions of cell growth. In membrane preparations, however, PGJ2 and delta 12PGJ2 failed to inhibit GTP gamma S (10 microM)- nor Ca2+ (1 mM)-induced accumulation of inositol phosphates. The site of PGJ2 or delta 12PGJ2 in inhibition of inositol phosphate accumulation would not be phospholipase C nor a putative GTP binding protein involved in activation of phospholipase C. The present results indicate that PGJ2 and delta 12PGJ2 inhibit cell growth in human astrocytoma cells and the inhibition of phosphoinositide turnover by these PGs might be involved in the inhibition of cell growth.

Astrocytoma↗
PubMed1989

Inhibitory effect of 8-bromo cyclic GMP on an extracellular Ca2+-dependent arachidonic acid liberation in collagen-stimulated rabbit platelets.

The inhibitory effect of cyclic GMP on collagen-induced platelet activation was studied using 8-bromo cyclic GMP (8brcGMP) in washed rabbit platelets. Addition of collagen (1 micrograms/ml) to platelet suspension caused shape change and aggregation associated with thromboxane (TX) A2 formation. 8brcGMP (10-1000 microM) inhibited collagen-induced platelet aggregation and TXA2 formation in a concentration-dependent manner. 8brcGMP did not affect platelet cyclooxygenase pathways, but markedly inhibited collagen-induced arachidonic acid (AA) liberation from membrane phospholipids in [3H]AA-prelabeled platelets, indicating that the inhibitory effect of 8brcGMP on collagen-induced aggregation is due to an inhibition of AA liberation. In [32P]orthophosphate-labeled platelets, collagen stimulated phosphorylation of a 20,000 dalton (20-kD) and 40-kD proteins. 8BrcGMP stimulated phosphorylation of a specific protein having molecular weight of 46-kD and inhibited collagen-induced both 20- and 40-kD protein phosphorylation. Collagen could stimulate the AA liberation without activation of phospholipase C or Na+-H+ exchange, but could not in the absence of extracellular Ca2+. These findings suggest that cyclic GMP inhibits collagen-induced AA liberation which is mediated by an extracellular Ca2+-dependent phospholipase A2. However, cyclic GMP seems to inhibit the Ca2+-activated phospholipase A2 indirectly, since 8brcGMP had no effect on Ca2+ ionophore A23187-induced platelet aggregation or AA liberation. It is therefore suggested that cyclic GMP may regulate collagen-induced increase in an availability of extracellular Ca2+ which is responsible for phospholipase A2 activation in rabbit platelets.

Animals↗
PubMed1989

Thromboxane A2 activates phospholipase C in astrocytoma cells via pertussis toxin-insensitive G-protein.

The properties of thromboxane A2 (TXA2) receptors were examined in 1321N1 human astrocytoma cells. 9,11-Epithio-11,12-methanothromboxane A2 (STA2), a stable analogue of TXA2, stimulated the accumulation of inositol phosphates (IPs) with an EC50 of about 50 nM. The STA2-induced accumulation of IPs was inhibited concentration dependently by ONO3708, a TXA2 receptor antagonist, with an inhibition constant (Ki) of about 10 nM. Inositol trisphosphate (IP3) was accumulated more rapidly than inositol bisphosphate (IP2) in response to STA2. HPLC analysis indicated that inositol 1,4,5-trisphosphate accumulated in the presence of STA2. STA2 alone had no effect on the accumulation of IPs in membrane preparations but it potentiated the accumulation induced by GTP gamma S. [3H]SQ29548, a TXA2 receptor antagonist, bound specifically to TXA2 receptors, expressing a single binding site with a dissociation constant (Kd) of 10.9 nM. The competition curve for STA2 inhibition of [3H]SQ29548 binding was shifted to the right and was steeper in the presence of GTP gamma S. Pertussis toxin (IAP) elicited ADP-ribosylation of 41KD protein but had no effect on the sensitivity to GTP of the STA2 inhibition of SQ29548 binding or of STA2-induced accumulation of IPs. It is concluded from these results that the stimulation of TXA2 receptors results in activation of phospholipase C via a GTP binding protein and that the protein is not a substrate for IAP.

Adenosine Diphosphate↗
PubMed1989

GTP gamma S binding activities were reduced in heavy membrane fraction during desensitization by Ca-mobilizing agonists in human astrocytoma cells.

Carbachol, histamine and bradykinin activate phospholipase C in pertussis toxin-insensitive manner in human astrocytoma cells. Pretreatments of the cells with these agonists resulted in the reduction of GTP gamma S-induced accumulation of inositol phosphates in membrane preparations. Treatment of cells with carbachol mobilized GTP gamma S binding activities as well as muscarinic receptors from heavy membrane fraction to light fraction, reflecting from an agonist-induced desensitization. The treatment of the cells with agonists reduced a 32 kDa GTP binding protein in heavy membrane fraction, determined by a photoaffinity labeling with [35S]GTP gamma S. The data suggest that the 32 kDa GTP binding protein is involved in desensitization by agonists which activate phospholipase C in human astrocytoma cells.

Affinity Labels↗
PubMed1988

Bradykinin-induced contraction is inhibited by tiaramide, an anti-inflammatory drug, with an inhibition of increase in intracellular free calcium.

The mechanism of bradykinin-induced contraction in rabbit urinary detrusor was investigated using an anti-inflammatory drug, tiaramide. The contraction as well as prostaglandin (PG) E2 release induced by bradykinin was abolished by treatment with indomethacin, indicating that the contraction was mediated by PGs. The accumulation of inositol phosphates (IP) by bradykinin was partly inhibited by treatment with indomethacin, suggesting that part of the IP accumulation was due to PGs. Although the remaining accumulation of IPs induced by bradykinin in the presence of indomethacin should elicit contraction in smooth muscle cells, indomethacin abolished bradykinin-induced contraction. The dissociation between indomethacin-induced inhibition of IP accumulation and contraction induced by bradykinin might be explained by the existence of PG-generating cells in addition to smooth muscle cells. Bradykinin stimulates phospholipase C, which leads to an increase in intracellular free Ca++, activation of phospholipase A2 and release of PGs in the PG-generating cells. The released PGs act on smooth muscle cells to elicit contractions via phospholipase C activation and Ca++ mobilization. Tiaramide inhibited the PGE2 release and contraction induced by bradykinin by reducing the arachidonic acid release from membrane phospholipid but did not have a direct effect on cyclo-oxygenase. Tiaramide reduced IP accumulation induced by bradykinin to an extent similar to indomethacin. However, tiaramide had no effect on IP accumulation induced by PGE2, although it potently inhibited the contraction induced by PGE2, which elicits contractions without affecting phospholipase A2. The rise in intracellular free Ca++ induced by PGE2 as well as bradykinin was inhibited by tiaramide.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Epidermal growth factor stimulates the rapid accumulation of inositol (1,4,5)-trisphosphate and a rise in cytosolic calcium mobilized from intracellular stores in A431 cells.

Exposure of A431 human epidermoid carcinoma cells to epidermal growth factor (EGF), bradykinin, and histamine resulted in a time- and concentration-dependent accumulation of the inositol phosphates (InsP) inositol monophosphate, inositol bisphosphate, and inositol trisphosphate (InsP3). Maximal concentrations of EGF (316 ng/ml; approximately 50 nM), bradykinin (1 microM), and histamine (1 mM) resulted in 3-, 6-, and 3-fold increases, respectively, in the amounts of inositol phosphates formed over a 10-min period. The K0.5 values for stimulation were approximately 10 nM, 3 nM, and 10 microM for EGF, bradykinin, and histamine, respectively. EGF and bradykinin stimulated the rapid accumulation of the two isomers of InsP3, Ins(1,3,4)P3, and Ins(1,4,5)P3 as determined by high performance liquid chromatography analysis; maximal accumulation of Ins(1,4,5)P3 occurred within 15 s. EGF and bradykinin also stimulated a rapid (maximal levels attained within 30 s after addition of hormone) and a sustained 4- and 6-fold rise, respectively, in cytosolic free Ca2+ levels as measured by Fura-2 fluorescence. EGF and bradykinin also produced a rapid, although transient, 3- and 5-fold increase, respectively, in cytosolic free Ca2+ after chelation of extracellular Ca2+ with 3 mM EGTA. These data are consistent with the idea that EGF elevates intracellular Ca2+ levels in A431 cells, at least in part, as a result of the rapid formation of Ins(1,4,5)P3 and the consequential release of Ca2+ from intracellular stores.

Bradykinin↗
PubMed1987

Regulation of inositol trisphosphate accumulation by muscarinic cholinergic and H1-histamine receptors on human astrocytoma cells. Differential induction of desensitization by agonists.

Although activation of muscarinic cholinergic receptors on 1321N1 human astrocytoma cells results in a linear accumulation of inositol phosphates for up to 60 min in the presence of LiCl [Masters, Quinn & Brown (1985) Mol. Pharmacol. 27, 325-332], activation of H1-histamine receptors resulted in an increase in total inositol phosphate formation that was maintained for less than 5 min. The effects of stimulation of these two receptors on accumulation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] and inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P4] were also examined. Incubation of 1321N1 cells with carbachol resulted in a rapid accumulation of all three inositol phosphates, reaching a maximum within 30 s; this elevated value was maintained for up to 60 min. The rate of disappearance of Ins(1,3,4)P3 from carbachol-treated cells after the addition of atropine paralleled or exceeded the rate of disappearance of Ins(1,4,5)P3. Although the initial rates of accumulation of Ins(1,4,5)P3, Ins(1,3,4)P3 and Ins(1,3,4,5)P4 in the presence of histamine were similar to that observed with carbachol, the amounts of these inositol phosphates had returned to control values within 5 min after the addition of histamine. The results indicate that, although the acute effects of muscarinic receptor and H1-histamine receptor stimulation on phosphoinositide hydrolysis are very similar, the histamine receptor is desensitized rapidly, whereas the muscarinic receptor is not. This effect on histamine-receptor function is apparently homologous, since preincubation of 1321N1 cells with histamine did not decrease the subsequent response to carbachol.

Astrocytoma↗
PubMed1987

Contribution of prostaglandin E2 to bradykinin-induced contraction in rabbit urinary detrusor.

Bradykinin (100 pM to 1 microM) contracted the rabbit urinary detrusor in vitro. The sensitivity to bradykinin was about 1000 times higher than that to acetylcholine (ACh) on a molar basis. The contractile response to bradykinin was unaffected by atropine, diphenhydramine, FPL-55712, methysergide, prazosin or tetrodotoxin, indicating that the contraction was not mediated via the release of ACh, histamine, peptide leukotrienes, serotonin or catecholamine. The bradykinin-induced contraction was, however, inhibited by indomethacin (5 microM), a cyclooxygenase inhibitor. Caffeic acid (10 microM), a lipoxygenase inhibitor, did not affect the contraction. Bradykinin (1 nM to 100 nM) stimulated the release of prostaglandin E2 from the detrusor in a concentration-dependent manner, and the release was abolished by treatment with indomethacin (5 microM). Prostaglandin (PG) E2 contracted the urinary detrusor with an EC50 of about 0.1 microM. Adenosine 5'-triphosphate (ATP), a stimulator of PG synthesis, also contracted the muscle with an EC50 of about 100 microM. [14C]Arachidonic acid was converted to PGE2 and F2 alpha when it was incubated with the 700 X g supernatant of the muscle homogenate. However, neither bradykinin nor ATP stimulated the PG synthesis in the supernatant. These results showed that bradykinin and ATP did not affect the cyclooxygenase and/or PG degradation system. On the other hand, when the intact detrusor muscle was incubated with [14C]arachidonic acid, bradykinin and ATP stimulated the PG synthesis, and the stimulated synthesis was inhibited by indomethacin. Mepacrine, a phospholipase A2 inhibitor, more potently inhibited the bradykinin- and ATP-induced contractions than the ACh-induced one.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1986

H1-histamine receptors on human astrocytoma cells.

The H1-histamine receptor antagonist [3H]mepyramine bound with high affinity (Kd = 3-5 nM) to membranes derived from 1321N1 human astrocytoma cells. The H1-receptor antagonists triprolidine and diphenhydramine inhibited [3H]mepyramine binding with Kj values of 1-5 nM, whereas the Kj of the H2-histamine receptor antagonist cimetidine was greater than 100 microM. Histamine also inhibited [3H]mepyramine binding to 1321N1 cell membranes, and the histamine inhibition curve was shifted to the right and steepened in the presence of 1 microM guanosine 5'-O-(3-thiotriphosphate). Treatment of 1321N1 cells with pertussis toxin had no effect on the capacity of histamine to inhibit [3H]mepyramine binding either in the absence or presence of guanosine 5'-O-(3-thiotriphosphate). Therefore, agonist-occupied histamine receptors in these cells apparently interact with a guanine nucleotide regulatory protein that is not the inhibitory guanine nucleotide regulatory protein of adenylate cyclase. Although adenylate cyclase activity was not affected by histamine in a cell-free preparation, incubation of 1321N1 cells with histamine resulted in an attenuation of cyclic AMP accumulation. Analysis of cyclic AMP degradation in the presence of histamine indicated that the effects of histamine on cyclic AMP accumulation are mediated through activation of phosphodiesterase. This idea was supported by the fact that the phosphodiesterase inhibitor 1-isobutyl 3-methylxanthine blocked attenuation of cyclic AMP accumulation by histamine in a noncompetitive manner. Histamine also markedly increased phosphoinositide breakdown and 45Ca2+ efflux in 1321N1 cells. These histamine-induced effects apparently are mediated through H1-receptors, since triprolidine, but not cimetidine, potently inhibited histamine action. As for histamine interaction with its receptor, pertussis toxin had no effect on histamine-induced phosphoinositide breakdown, 45Ca2+ efflux, or attenuation of cyclic AMP accumulation. Taken together, these data indicate that 1321N1 human astrocytoma cells are a useful model system for the study of H1-histamine receptors and the biochemical responses mediated through these receptors.

1-Methyl-3-isobutylxanthine↗