Homologous and heterologous desensitization of histamine H1- and ATP-receptors in the smooth muscle cell line, DDT1MF-2: the role of protein kinase C

Cumulated Ca2+ spike duration underlies Ca2+ oscillation frequency-regulated NFκB transcriptional activity

[Ca2+]i oscillations drive downstream events, like transcription, in a frequency-dependent manner. Why [Ca2+]i oscillation frequency regulates transcription has not been clearly revealed. A variation in [Ca2+]i oscillation frequency apparently leads to a variation in the time duration of cumulated [Ca2+]i elevations or cumulated [Ca2+]i spike duration. By manipulating [Ca2+]i spike duration, we generated a series of [Ca2+]i oscillations with the same frequency but different cumulated [Ca2+]i spike durations, as well as [Ca2+]i oscillations with the different frequencies but the same cumulated [Ca2+]i spike duration. Molecular assays demonstrated that, when generated in ‘artificial’ models alone, under physiologically simulated conditions or repetitive pulses of agonist exposure, [Ca2+]i oscillation regulates NFκB transcriptional activity, phosphorylation of IκBα and Ca2+-dependent gene expression all in a way actually dependent on cumulated [Ca2+]i spike duration whether or not frequency varies. This study underlines that [Ca2+]i oscillation frequency regulates NFκB transcriptional activity through cumulated [Ca2+]i spike-duration-mediated IκBα phosphorylation.

Selective regulation of H1 histamine receptor signaling by G protein-coupled receptor kinase 2 in uterine smooth muscle cells

Histamine stimulates uterine contraction; however, little is known regarding the mechanism or regulation of uterine histamine receptor signaling. Here we investigated the regulation of Galpha(q/11)-coupled histamine receptor signaling in human myometrial smooth muscle cells using the inositol 1,4,5-trisphosphate biosensor pleckstrin homology domain of phospholipase-delta1 tagged to enhanced green fluorescent protein and the Ca(2+)-sensitive dye Fluo-4. Histamine addition caused concentration-dependent increases in inositol 1,4,5-trisphosphate and [Ca(2+)](i) in the ULTR human uterine smooth muscle cell line and primary human myometrial cells. These effects were completely inhibited by the H(1) histamine receptor antagonist, diphenhydramine, and were unaffected by the H(2) histamine receptor antagonist, cimetidine. ULTR and primary myometrial cells were transfected with either dominant-negative G protein-coupled receptor kinases (GRKs) or small interfering RNAs targeting specific GRKs to assess the roles of this protein kinase family in H(1) histamine receptor desensitization. Dominant-negative GRK2, but not GRK5 or GRK6, prevented H(1) histamine receptor desensitization. Similarly, transfection with short interfering RNAs (that each caused >70% depletion of the targeted GRK) for GRK2, but not GRK3 or GRK6, also prevented H(1) histamine receptor desensitization. Our data suggest that histamine stimulates phospholipase C-signaling in myometrial smooth muscle cells through H(1) histamine receptors and that GRK2 recruitment is a key mechanism in the regulation of H(1) histamine receptor signaling in human uterine smooth muscle. These data provide insights into the in situ regulation of this receptor subtype and may inform pathophysiological functioning in preterm labor and other conditions involving uterine smooth muscle dysregulation.

Potentiation by neuropeptide Y of histamine H1 receptor-mediated contraction in rat blood vessels

Histamine-induced contraction and its potentiation by neuropeptide Y were investigated in rat blood vessels. Rat arteries and veins constricted with single concentrations of histamine dose-dependently (0.1-100 microM). This histamine-induced contraction immediately desensitized. Histamine H1 receptor antagonists, 1 microM mepyramine and 1 microM diphenhydramine, abolished this transient contraction completely, whereas cimetidine, phentolamine, reserpine and tetrodotoxin failed to inhibit the contraction. Histamine H1 receptor mRNA level by reverse transcription-polymerase chain reaction was quite parallel to histamine H1 receptor-mediated contraction, indicating that the contraction is mediated through histamine H1 receptors in the smooth muscle. Neuropeptide Y (10 nM in arteries and 3 nM in veins, respectively) significantly potentiated histamine H1 receptor-mediated contraction via neuropeptide Y1 receptors in most of rat blood vessels. Since the phospholipase C inhibitors, neomycin (1 mM) and 2-nitro-4-carboxyphenyl-N, N-diphenylcarbamate (NCDC, 10 microM), respectively, specifically abolished the potentiation, the potentiation by neuropeptide Y may depend on activation of phospholipase C.

Clathrin-independent internalization of the human histamine H1-receptor in CHO-K1 cells

The aim of the present study was to investigate the cellular pathway involved in histamine-stimulated internalization of the human H1-receptor in CHO-K1 cells expressing N-terminal myc-tagged H1-receptor (Myc-H1) or N-terminal myc-C-terminal green fluorescent protein (Myc-GFP H1) versions of the receptor. Studies of 3H-mepyramine binding and histamine-stimulated 3H-inositol phosphate accumulation in these cells showed that the Myc-H1 and Myc-GFP H1-receptors had identical pharmacology to the wild-type H1-receptor. The Myc-H1-receptor was rapidly internalized in CHO-K1 cells following stimulation with histamine (0.1 mM). This response occurred within 15 min, and could be prevented by the quaternary H1-receptor antagonist alpha-pirdonium. Similar data were obtained with the Myc-GFP H1-receptors. Internalization of the Myc-GFP H1-receptor was maintained in the absence of extracellular calcium and was not inhibited by the CAM kinase II inhibitor KN-62 (10 microM). Phorbol dibutyrate, an activator of protein kinase C, was also able to stimulate internalization of the H1-receptor. However, inhibition or downregulation of protein kinase C (which significantly modified histamine-stimulated inositol phosphate responses) was without effect on the internalization of the H1-receptor stimulated by histamine. Hypertonic sucrose did not prevent histamine-induced internalization of the Myc-GFP H1-receptor, but was able to attenuate internalization of transferrin via clathrin-mediated endocytosis in the same cells. In contrast, preincubation of cells with filipin or nystatin, which disrupts caveolae and lipid rafts, completely inhibited the histamine-induced internalization of the Myc-GFP H1-receptor, but was without effect on the sequestration of transferrin. The H1-receptor and cholera toxin subunit B were colocalized under resting conditions at the cell surface. Immunohistochemical studies with an antibody to caveolin-1 confirmed that this protein was also localized predominantly to the plasma membrane. However, following stimulation of CHO-Myc-GFP H1 cells with histamine, there was no evidence for internalization of caveolin-1 in parallel with the H1-receptor. These data provide strong evidence that the H1-receptor is internalized via a clathrin-independent mechanism and most likely involves lipid rafts.

Endogenous signalling system involved in parotid gland adenosine A(1) receptor-amylase release

AIM

In this study, we have determined signalling pathways involved in adenosine A(1) receptor (A(1) receptor)-dependent stimulation of amylase release in rat parotid gland.

METHODS

Amylase release, binding and cyclic adenosine monophosphate (cAMP) assays, inositol phosphates (IPs) production and nitric oxide synthase (NOS) activity in the presence of cyclopentyl-1,3-dipropylxanthine (CPA) alone or in the presence of different inhibitory drugs were performed.

RESULTS

The binding parameters of specific A(1) antagonist [(3)H]-cyclopentyl 1,3-dipropilxanthine ([(3)H]-DPCPX) in parotid gland membranes show a population of high affinity sites with K(d) (nm) 0.53 +/- 0.06 and B(max) (fmol mg(-1) protein) 122.6 +/- 10.2. CPA stimulation of A(1) receptor exerts an increase in amylase release, IPs accumulation, cAMP production and NOS activity. All these A(1) agonist effects were blocked by the A(1) receptor antagonist DPCPX. Inhibitors of phospholipase C (PLC), calcium/calmodulin (CaM), protein kinase C (PKC), and adenylate cyclase, but not NOS, activities attenuated the CPA stimulatory effect on amylase release. The effect of CPA on amylase release significantly correlated with its action either on cAMP or on IPs accumulation.

CONCLUSION

These results suggest that CPA activation of parotid gland A(1) receptor induces a stimulatory effect on amylase release associated with increased production of cAMP and IPs accumulation. The mechanism appears to occur secondarily to stimulation of phosphoinositide turnover via PLC activation. This, in turn, triggers cascade reactions involving CaM and PKC. The CPA stimulation of NOS does not appear to participate in amylase release.

International Union of Pharmacology. XXV. Nomenclature and classification of adenosine receptors

Four adenosine receptors have been cloned and characterized from several mammalian species. The receptors are named adenosine A(1), A(2A), A(2B), and A(3). The A(2A) and A(2B) receptors preferably interact with members of the G(s) family of G proteins and the A(1) and A(3) receptors with G(i/o) proteins. However, other G protein interactions have also been described. Adenosine is the preferred endogenous agonist at all these receptors, but inosine can also activate the A(3) receptor. The levels of adenosine seen under basal conditions are sufficient to cause some activation of all the receptors, at least where they are abundantly expressed. Adenosine levels during, e.g., ischemia can activate all receptors even when expressed in low abundance. Accordingly, experiments with receptor antagonists and mice with targeted disruption of adenosine A(1), A(2A), and A(3) expression reveal roles for these receptors under physiological and particularly pathophysiological conditions. There are pharmacological tools that can be used to classify A(1), A(2A), and A(3) receptors but few drugs that interact selectively with A(2B) receptors. Testable models of the interaction of these drugs with their receptors have been generated by site-directed mutagenesis and homology-based modelling. Both agonists and antagonists are being developed as potential drugs.

Adenosine triphosphate-evoked cytosolic calcium oscillations in human granulosa-luteal cells: role of protein kinase C

ATP has been shown to modulate progesterone production in human granulosa-luteal cells (hGLCs) in vitro. After binding to a G protein-coupled P2 purinergic receptor, ATP stimulates phospholipase C. The resultant production of diacylglycerol and inositol triphosphate activates protein kinase C (PKC) and intracellular calcium [Ca(2+)](i) mobilization, respectively. In the present study, we examined the potential cross-talk between the PKC and Ca(2+) pathway in ATP signal transduction. Specifically, the effect of PKC on regulating ATP-evoked [Ca(2+)](i) oscillations were examined in hGLCs. Using microspectrofluorimetry, [Ca(2+)](i) oscillations were detected in Fura-2 loaded hGLCs in primary culture. The amplitudes of the ATP-triggered [Ca(2+)](i) oscillations were reduced in a dose-dependent manner by pretreating the cells with various concentrations (1 nM to 10 microM) of the PKC activator, phorbol-12-myristate-13-acetate (PMA). A 10 microM concentration of PMA completely suppressed 10 microM ATP-induced oscillations. The inhibitory effect occurred even when PMA was given during the plateau phase of ATP evoked [Ca(2+)](i) oscillations, suggesting that extracellular calcium influx was inhibited. The role of PKC was further substantiated by the observation that, in the presence of a PKC inhibitor, bisindolylmaleimide I, ATP-induced [Ca(2+)](i) oscillations were not completely suppressed by PMA. Furthermore, homologous desensitization of ATP-induced calcium oscillations was partially reversed by bisindolylmaleimide I, suggesting that activated PKC may be involved in the mechanism of desensitization. These results demonstrate that PKC negatively regulates the ATP-evoked [Ca(2+)](i) mobilization from both intracellular stores and extracellular influx in hGLCs and further support a modulatory role of ATP and P2 purinoceptor in ovarian steroidogenesis.

Possible contribution of protein kinase C in the effects of histamine on the visceral nociceptor activities in vitro

To clarify the possible contribution of protein kinase C activation in histamine-induced excitation and sensitization of the heat response of testicular polymodal receptors, the effects of staurosporine, a protein kinase C inhibitor, and phorbol 12,13-dibutyrate, a protein kinase C activating phorbol ester, were studied in visceral polymodal receptors. Single polymodal receptor activities were recorded in vitro from testis-spermatic nerve preparations obtained from deeply anesthetized dogs (pentobarbital sodium, 30 mg/kg, i.v.). Histamine (10 microM)-induced excitation and facilitation of the heat response of polymodal receptors were both suppressed by staurosporine (1 microM), suggesting that activation of protein kinase C is involved in both these effects of histamine. Application of phorbol 12,13-dibutyrate (0.1 microM) mixed with histamine increased the histamine-induced excitation, whereas a 5 min application of phorbol 12,13-dibutyrate before histamine suppressed it. These results suggest that phorbol 12,13-dibutyrate-activated protein kinase C has inactivation as well as activation effects on the intracellular cascade connected to histamine receptors, and that the former has a slower time course.

Desensitization of the histamine H1-receptor and transcriptional down-regulation of histamine H1-receptor gene expression in bovine tracheal smooth muscle

We have investigated the role of protein kinase C (PKC) in the desensitization of histamine H1-receptors and in the expression of the histamine H1-receptor gene in airway smooth muscle. Prolonged 4beta-phorbol 12,13 dibutyrate (PDBu) pretreatment (4 h, 100 nM-1 microM) of bovine trachealis caused a concentration-dependent loss of contraction in response to histamine H1-receptor stimulation, which was associated with a concentration-dependent decrease in histamine-induced total [3H]-inositol phosphates accumulation. In contrast, the responses to sodium fluoride, a direct G-protein activator, were unalterd by PDBu (100-300 nM) pre-incubation and only slightly reduced following incubation with 1 microM PDBu. A selective PKC inhibitor, GF 109203X, partially blocked the PDBu (1 microM)-induced desensitization and completely blocked the effect of 100 nM PDBu, confirming the involvement of PKC. Binding experiments using [3H]-pyrilamine revealed a class of high-affinity binding sites within the range for the histamine H1 receptor in airway smooth muscle. PDBu (1 microM) pretreatment for 4 h did not change the number of histamine H1 receptors. PDBu (1 microM) exposure caused a time-dependent reduction in the steady-state levels of histamine H1-receptor mRNA, which was inhibited by pre-incubation with GF 109203X and by cycloheximide, a protein synthesis inhibitor. Nuclear run-on assays revealed a 50% reduction in the rate of histamine H1-receptor gene transcription after 17 h PDBu pretreatment, whereas mRNA stability was not affected by PDBu pretreatment (17 h). In conclusion, we have shown a PKC-mediated desensitization of the histamine H1-receptor in BTSM and a transcriptional down-regulation of the histamine H1-receptor gene expression, which requires new protein synthesis.

Primitivism and plasticity of pain--implication of polymodal receptors

Bio-warning and defense mechanisms play the most fundamental roles in living organisms. From an evolutionary point of view, nociceptive systems are very primitive and are richly provided with humoral signaling mechanisms of aboriginal humoral defense systems, as reflected in the primitive nature of the polymodal receptor, a poorly differentiated sensory receptor signaling nociceptive information. Recent advances in studies on pain have made it possible to explain neural mechanisms of pain systems under physiological conditions and reveal that there is a large gap between physiological and pathological pains. Protracted nociceptive inputs under pathological conditions induce plastic, either functional or structural, alterations in the nociceptive pathways. These plastic changes lead to crosstalk among the neural networks, including circuits related to motor, autonomic, or psychological functions. These plastic changes, once established, persist even after the original pain sources disappear in a memory-like fashion. Thus, it is revealed that chronic pain cannot be treated by blocking pain pathways, which is effective against acute pain, but require treatment from a multidisciplinary perspective.

Regulation of H1-receptor coupling and H1-receptor mRNA by histamine in bovine tracheal smooth muscle

1. Pretreatment of bovine tracheal smooth muscle (BTSM) with histamine (1-100 microM, 1 h) induced a concentration-dependent desensitization of the contractile response to subsequently administered histamine, with a reduction of the maximum response of 72 +/- 8% (n = 5) following pre-exposure to 100 microM histamine. In contrast, concentration-response curves to the muscarinic agonist, methacholine were not affected following histamine pretreatment, indicating a homologous desensitization. Furthermore, concentration-response curves to NaF, a G-protein activator, were not altered following histamine pre-incubation. 2. The histamine H1-receptor (H1R) desensitization could be antagonized by mepyramine (an H1-receptor antagonist, 1 microM) but not by cimetidine (an H2-receptor antagonist, 10 microM), indicating that the desensitization occurred via stimulation of histamine H1-receptors, without evidence for the involvement of histamine H2-receptors. 3. Indomethacin (10 microM) did not block the H1R desensitization, suggesting no involvement of prostaglandins. Furthermore, histamine pre-incubation in calcium free medium still induced a functional uncoupling of H1R. 4. GF 109203X, a protein kinase C (PKC) inhibitor, and H-7, a non-selective kinase inhibitor, did not antagonize the homologous H1R desensitization. 5. The steady-state level of H1R mRNA, assessed by Northern blot analysis, was not affected by prolonged histamine exposure (100 microM, 0.5, 1, 2, 4, 16 and 24 h). 6. These results suggest that histamine induces desensitization of the H1R at the level of the receptor protein, which involves a mechanism independent of PKC, PKA, PKG and calcium influx, suggesting the involvement of a receptor-specific kinase.

Dual effects of histamine and substance P on intracellular calcium levels in human U373 MG astrocytoma cells: role of protein kinase C

1. In human U373 MG astrocytoma cells agonist-induced increases in intracellular Ca2+ ([Ca2+]i) are rapidly returned towards prestimulated levels. Examination of the effect of histamine and substance P on [Ca2+]i in thapsigargin-treated cells has allowed a mechanism contributing to this effect to be characterized. 2. Histamine and substance P stimulated [3H]-inositol monophosphate ([3H]-IP1) accumulation in U373 MG cells. Concentration-response curves of [3H]-IP1 accumulation in suspensions of U373 MG cells in HEPES buffer containing 30 mM Li+ yielded best-fit EC50 values of 19.1+/-1.5 microM for histamine and 5.7+/-1.3 nM for substance P. 3. In confluent monolayers of fura-2 loaded U373 MG cells perfusion with 100 microM histamine resulted in a transient 597+/-50 nM increase in [Ca2+]i. The best-fit EC50 for histamine was 4.6+/-2.2 microM. The initial, transient, histamine response was often followed by further small transient increases in [Ca2+]i. 4. Treatment of U373 MG cells with 5 microM thapsigargin, followed by the readdition of 1.8 mM Ca2+ to the perfusion buffer, resulted in a steady-state level of [Ca2+]i 97+/-5 nM above pretreated levels (measured 400 s after readdition of Ca2+). Perfusion of histamine (100 microM, 100 s) caused a rapid decline in the thapsigargin-induced steady state level of [Ca2+]i. This effect of histamine was normally reversible upon washout. The best-fit EC50, for the histamine response was 0.8+/-0.2 microM. Substance P (10 nM, 100s) also caused a reduction in thapsigargin-induced steady-state levels of [Ca2+]i. 5. Neither 100 microM histamine nor 10 nM substance P inhibited the rate of quench of fura-2 fluorescence by Mn2+ in U373 MG cells pretreated with 5 microM thapsigargin, indicating that the depressant effect on steady-state raised [Ca2+]i was probably not due to a block of Ca2+ entry. 6. The depressant effect of histamine on [Ca2+]i was blocked by 1 microM mepyramine, and was partially reduced by pre-incubation with 1 microM staurosporine (61+/-7% reduction) and with Ro 31-8220 (24+/-10% and 50+/-6% reduction by 1 and 10 microM Ro 31-8220, respectively). Pre-incubation with H-89 did not alter the depressant effect of histamine. 7. Neither 1 microM staurosporine nor 10 microM KN-62 inhibited the binding of [3H]-mepyramine to guinea-pig cerebellar membranes, whereas it was reduced by 17+/-1% and 55+/-2% by 1 and 10 microM Ro 31-8220, respectively. However, [3H]-IP1 accumulation stimulated by histamine in U373 MG cells was not inhibited by 1 or 10 microM Ro 31-8220 and in 2 out of 3 experiments there was a significant potentiation of the response to histamine with both concentrations of Ro 31-8220. Staurosporine, 1 microM, similarly potentiated the response to 100 microM histamine in 3 out of 4 experiments. KN-62 (10 microM) did not stimulate histamine-induced [3H]-IP1 accumulation. 8. In HEPES buffer to which no Ca2+ had been added, histamine stimulated a transient 451+/-107 nM increase in [Ca2+]i. Pretreatment with 1 microM and 10 microM Ro 31-8220 did not significantly alter the initial peak response to histamine, but slowed the rate at which histamine-induced increases in [Ca2+]i were returned to prestimulated levels. Pretreatment with KN-62 had no significant effect on the response to histamine, but consistently inhibited the secondary slower phase of the decline in [Ca2+]i. H-89 did not alter the histamine response. 9. The effect of histamine in stimulating Ca2+ extrusion was not confined to U373 MG cells, since 100 microM histamine also caused a rapid decrease in steady-state levels of [Ca2+]i in thapsigargin-treated human HeLa cells. 10. The results indicate that agonists which increase [Ca2+]i via activation of phosphoinositide metabolism can also stimulate a homeostatic mechanism which acts to reduce [Ca2+]i. The balance of the evidence indicates that in U373 MG cells the latter effect most likely involves a PKC-mediated stimulation of a Ca2+-extrusion pump.

Involvement of protein kinase C in homologous desensitization of histamine-evoked secretory responses in rat chromaffin cells

The secretory responses in rat adrenal chromaffin cells to histamine H1 receptor stimulation desensitize during repetitive stimulation. The rate of development of this desensitization was slowed by Ro 31-8220, a protein kinase C (PKC) inhibitor. Ro 31-8220 also reversed part of the desensitization which had been induced by earlier histamine stimulation. Phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C, inhibited histamine-evoked catecholamine (CA) secretion almost completely. The inhibitory effect of PDBu on the H1-receptor-mediated secretory response was antagonized by Ro 31-8220. Histamine induced [Ca2+]i increases due to Ca2+ entry and Ca2+ release from intracellular Ca2+ stores in fura-2-loaded adrenal medullary cells. These [Ca2+]i increases were abolished in PDBu-treated cells. These results suggest that the activation of PKC following histamine H1 receptor stimulation plays a significant role in the process of homologous desensitization of histamine-evoked secretory responses in rat chromaffin cells, through modulation by PKC of H1 receptors and/or GTP-binding proteins coupled with H1 receptors.

Heterologous desensitization of smooth muscle to K+ depolarization: retarded stimulus-[Ca2+]i coupling

To understand the phenomenon of postreceptor heterologous desensitization, we exposed porcine carotid media to 40 mM KCl physiological saline solution both before and after intervening treatment with histamine. Increasing histamine concentration or duration of exposure or decreasing the interval between histamine exposure and KCl progressively slowed the contractile responses to K+ depolarization. A delay in initiation and a slower rate of rise of KCl-induced stress in histamine-pretreated muscle were preceded by a slower rate of rise of aequorin-estimated myoplasmic Ca2+ concentration ([Ca2+]i), myosin regulatory light chain (MRLC) phosphorylation, and tissue stiffness, with no detectable change in the Ca2+ sensitivity of MRLC phosphorylation. This heterologous desensitization was not a diminished steady-state force but instead a profound slowing of contraction rates. This slowing was a manifestation of retardation of the rate at which [Ca2+]i rises to the level appropriate for the stimulus. The lack of rapid initial [Ca2+]i and cross-bridge phosphorylation transients as a consequence of histamine pretreatment resulted in very slow cross-bridge cycling rates and rates of force development (latch).

Bradykinin regulates the histamine-induced Ca2+ mobilization via protein kinase C activation in human gingival fibroblasts

We previously demonstrated that histamine and bradykinin evoke an increase in intracellular Ca2+ ([Ca2+]i) in human gingival fibroblasts by using a fluorescent Ca2+ indicator Fura-2. In this paper, we further demonstrate the regulation of the histamine-induced Ca2+ mobilization by bradykinin. In fibroblasts stimulated with bradykinin (1 microM), subsequent stimulation with histamine (100 microM) failed to mobilize Ca2+, whereas bradykinin induced an increase in [Ca2+]i in the cells pre-stimulated with histamine. The attenuation of the histamine response was dependent on the concentration of bradykinin for the first stimulation. Histamine also failed to induce the formation of inositol 1,4,5-trisphosphate in fibroblasts pretreated with bradykinin. In fibroblasts pretreated with bradykinin (1 microM) for 3 min and then washed with fresh medium, the effect of histamine on [Ca2+]i quickly returned to the control level. The activation of protein kinase C by phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (PMA) elicited a marked decrease in histamine-induced Ca2+ mobilization. When the protein kinase C activity was inhibited with H7, a protein kinase C inhibitor, or was down-regulated by pretreatment with PMA for 20 h, the inhibitory effect of PMA on the histamine response was relieved. In the fibroblasts pretreated with H7 or PMA for 20 h, histamine evoked Ca2+ mobilization even after bradykinin stimulation. These results suggest that the histamine response is regulated by bradykinin receptor activation via the activation of protein kinase C in human gingival fibroblasts.

The effect of the PKC inhibitor GF109203X on the release of Ca2+ from internal stores and Ca2+ entry in DDT1 MF-2 cells

1. The effects of the specific protein kinase C (PKC) inhibitor, GF109203X, were measured on the cytoplasmic Ca2+ concentration ([Ca2+]i), and on histamine H1 receptor- and thapsigargin-mediated increases in [Ca2+]i in DDT1 MF-2 smooth muscle cells. 2. After pretreatment of cells with GF109203X (5 microM, 45 min), the histamine (100 microM)-induced initial rise in [Ca2+]i, representing Ca2+ mobilization from internal stores, was inhibited (by 59 +/- 7%). The slowly declining phase of the histamine induced Ca2+ response, reflecting Ca2+ entry, was enhanced (83 +/- 26%) in the presence of the PKC inhibitor. 3. The histamine induced release of Ca2+ from internal stores, measured after blocking Ca2+ entry with LaCl3 was inhibited by GF109203X in a concentration-dependent manner (IC50: 3.1 +/- 1.1 microM). 4. Histamine-induced formation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) was not changed in the presence of GF109203X. 5. The PKC activating phorbol ester, phorbol 12-myristate 13-acetate (PMA, 1 microM), strongly reduced histamine-induced Ins(1,4,5)P3 formation (58 +/- 16%). This effect was reversed by GF109203X (5 microM). Furthermore, PMA diminished histamine evoked Ca2+ release (50 +/- 6%) and blocked Ca2+ entry completely. 6. The rise in [Ca2+]i caused by blocking endoplasmic reticulum Ca2(+)-ATPase with thapsigargin (1 microM), was strongly reduced (57 +/- 3%) after pretreatment of cells with GF109203X. Downregulation of PKC by long-term pretreatment of cells with PMA (1 microM, 48 h) did not abolish this effect of GF109203X (48 +/- 3% inhibition). 7. In permeabilized DDT, MF-2 cells preloaded with 45Ca2+ in the presence of GF109203X, the amount of 45Ca2+ released by Ins(1,4,5)P3 (10 microM) was markedly reduced (42 +/- 9%). GF109203X did not release Ca2+ itself and did not impair Ins(1,4,5)P3 receptor function. 8. Uptake of 45Ca2+ by intact cells, representing Ca2+ entry, was enhanced by GF109203X (65 +/- 11%), by histamine (24 +/- 6%) and also by thapsigargin (121 +/- 10%). The GF109203X- and the thapsigargin-induced uptake of 45Ca2+ were not additive. 9. These data suggest that GF109203X reduces the filling-state of intracellular Ins(1,4,5)P3 sensitive Ca2+ stores by inhibiting the Ca2+ uptake into these stores, thereby promoting store-dependent (capacitive) Ca2+ entry.

The histamine H1 receptor in GT1-7 neuronal cells is regulated by calcium influx and KN-62, a putative inhibitor of calcium/calmodulin protein kinase II

1. In GT1-7 cells, histamine stimulated the initial [Ca2+]i transient in a dose-dependent manner with a best-fit EC50 value of 4.2 +/- 4.2 microM (mean +/- s.e.mean, n = 4) and a best-fit maximal effect of 138 +/- 56 nM (n = 4) increase above basal calcium levels. 2. Pretreatment of cells with 30 microM histamine for 30 min desensitized the population mean peak calcium signal by 53% to 75 +/- 9 nM, (n = 3, P < 0.04). Analysis of the individual cells revealed that 39 +/- 7% (n = 94 cells from 8 experiments) of pretreated cells exhibited desensitized histamine-stimulated [Ca2+]i transients of < or = 1 standard deviation below the control cells mean calcium transient level. 3. The desensitization induced by histamine was prevented (P < 0.01) by KN-62 (10 microM), a putative inhibitor of the calcium/calmodulin-dependent protein kinase II (CaMKII). KN-62 (10 microM) alone did not induce [Ca2+]i mobilization, nor did it antagonize the histamine-stimulated [Ca2+]i signal. In addition, KN-62 did not appear to have its effect by hastening the rate of recovery from desensitization. 4. Histamine pretreatment in nominal (zero calcium + 0.2 mM EGTA) or in low (0.3 mM) extracellular calcium did not induce histamine receptor desensitization, supporting a role for extracellular calcium in the homologous H1 receptor desensitization process. 5. Histamine (30 microM) stimulated at least four different types of [Ca2+]i signals in GT1-7 cells. The majority (61%) were of single spikes with the remaining cells showing some form of calcium oscillatory behaviour. The proportion of GT1-7 cells showing histamine-induced calcium oscillations was histamine concentration-dependent and significantly reduced after acute desensitization. KN-62, when present during histamine pretreatment, prevented this fall in calcium oscillation. Under the conditions of nominal or 0.3 mM extracellular calcium the proportion of cells exhibiting histamine-stimulated calcium oscillations was not significantly different from the controls. 6. Bradykinin stimulated a [Ca2+]i transient in GT1-7 cells with a population mean peak response of 147 +/- 8 nM (n = 5) over basal levels. The bradykinin-induced [Ca2+]i signal was without any calcium oscillatory activity. Histamine pretreatment caused the heterologous desensitization of the bradykinin [Ca2+]i signal (44% reduction, P < 0.007), which was unaffected by KN-62. 7. The results presented here suggest that the histamine-mediated homologous H1 receptor desensitization process involves extracellular calcium and can be blocked by KN-62, a putative inhibitor of CaMKII. In contrast, KN-62 does not appear to prevent the histamine-mediated heterologous desensitization cascade. These findings suggest fundamental differences in the mechanisms underlying homologous and heterologous H1 receptor desensitization pathways in GT1-7 neuronal cells.

Regulation of histamine H1 receptor coupling by dexamethasone in human cultured airway smooth muscle

1. The regulation of histamine-induced [3H]-inositol phosphate and intracellular calcium responses in human cultured airway smooth muscle cells was studied. 2. Histamine induced concentration-dependent [3H]-inositol phosphate formation (EC50 4 microM). This response was inhibited by a range of selective H1 receptor antagonists but not by the H2-selective antagonist, tiotidone or the H3 receptor-selective antagonist, thioperamide, indicating that an H1 receptor is involved in this response in human cultured airway smooth muscle cells. 3. Preincubation of human cultured airway smooth muscle cells with concentrations of dexamethasone > 10 nM for 22 h produced concentration-dependent inhibition of histamine-induced inositol phosphate formation. The maximum inhibition observed was 45% of the response in control cells. The inhibitory effect of dexamethasone was itself reversed by prior exposure to the glucocorticoid receptor antagonist, RU38486 (10 microM). Preincubation for 22 h with 1 microM dexamethasone produced inhibition of the inositol phosphate response to histamine to all concentrations of histamine inducing significant inositol phosphate formation in these cells. In contrast, the response to the G protein activator, NaF (0.1-20 mM) was unaltered by preincubation with dexamethasone. 4. Preincubation of human airway smooth muscle cells with 1 microM dexamethasone for time periods of < 6 h failed to inhibit histamine-induced inositol phosphate formation in human airway smooth muscle cells. 5. Histamine also induced concentration-dependent elevation of intracellular calcium levels in Fura 2-loaded human airway smooth muscle cells. This response was inhibited by preincubation with 1 microM dexamethasone. 6. We conclude that signal transduction through the H1 receptor in human airway smooth muscle is subject to regulation by dexamethasone and that this may in part account for the protective effect of dexamethasone against spasmogen-induced contractile responses in the airways.

Increased desensitization by picomolar phorbol ester of the endothelium-mediated effect of histamine in the perfused rat mesenteric bed

The vasodilatatory, endothelium-mediated, effect of histamine (H), through H1 receptor, in the isolated and perfused mesenteric bed of the rat, undergoes strong desensitization during perfusion or repetitive injections of noradrenaline (NA) and H. The mesenteric bed completely desensitized to H is responsive to carbachol (C) and this latter compound does not affect the H desensitization. The homologous desensitization to C effect is very small, attaining less than 10% after 30 min of continuous perfusion. In this work the effect of inhibitors or activators of protein-kinase(s)-C (PKC) are studied during continuous perfusion of H or C in preparations preconstricted by NA. Staurosporine antagonizes the onset of the H desensitization, while the rate of desensitization in increased by phorbol-12-myristate-13-acetate (PMA). PMA, at a concentration from 10(-12) to 10(-10)M, selectively enhances the homologous desensitization of H, while at 10(-8)M it also produces a desensitization to C. At least two different PKC isoenzymes might be involved in the desensitization of the vasodilatatory effect of H and C in the isolated and perfused rat mesenteric bed.

Effect of different G protein-coupled receptor kinases on phosphorylation and desensitization of the alpha1B-adrenergic receptor

The alpha1B-adrenergic receptor (alpha1BAR), its truncated mutant T368, different G protein-coupled receptor kinases (GRK) and arrestin proteins were transiently expressed in COS-7 or HEK293 cells alone and/or in various combinations. Coexpression of beta-adrenergic receptor kinase (betaARK) 1 (GRK2) or 2 (GRK3) could increase epinephrine-induced phosphorylation of the wild type alpha1BAR above basal as compared to that of the receptor expressed alone. On the other hand, overexpression of the dominant negative betaARK (K220R) mutant impaired agonist-induced phosphorylation of the receptor. Overexpression of GRK6 could also increase epinephrine-induced phosphorylation of the receptor, whereas GRK5 enhanced basal but not agonist-induced phosphorylation of the alpha1BAR. Increasing coexpression of betaARK1 or betaARK2 resulted in the progressive attenuation of the alpha1BAR-mediated response on polyphosphoinositide (PI) hydrolysis. However, coexpression of betaARK1 or 2 at low levels did not significantly impair the PI response mediated by the truncated alpha1BAR mutant T368, lacking the C terminus, which is involved in agonist-induced desensitization and phosphorylation of the receptor. Similar attenuation of the receptor-mediated PI response was also observed for the wild type alpha1BAR, but not for its truncated mutant, when the receptor was coexpressed with beta-arrestin 1 or beta-arrestin 2. Despite their pronounced effect on phosphorylation of the alpha1BAR, overexpression of GRK5 or GRK6 did not affect the receptor-mediated response. In conclusion, our results provide the first evidence that betaARK1 and 2 as well as arrestin proteins might be involved in agonist-induced regulation of the alpha1BAR. They also identify the alpha1BAR as a potential phosphorylation substrate of GRK5 and GRK6. However, the physiological implications of GRK5- and GRK6-mediated phosphorylation of the alpha1BAR remain to be elucidated.

Regulation of the human histamine H1 receptor stably expressed in Chinese hamster ovary cells

1. The human H1 receptor gene expressed in Chinese hamster ovary cells (CHOhumH1) encodes a classical histamine H1 receptor with a pharmacology similar to that of the H1 receptor found in guinea-pig cerebellum and the endogenously expressed human H1 receptor in 1321N1 astrocytoma cells as determined by [3H]-mepyramine binding studies. 2. In CHOhumH1 cells, histamine induced a concentration-dependent rise in inositol phosphates (EC50 2.23 +/- 0.97 microM) and a rapid increase of [Ca2+]i, followed by a sustained increase of [Ca2+]i upon addition of 100 microM histamine. 3. Short-term exposure of CHOhumH1 cells to histamine (100 microM) resulted in a decrease of subsequent histamine-induced Ca2+ responses. The histamine-induced desensitization appeared to be heterologous as the ATP-induced Ca2+ response was also found to be affected. 4. The process of heterologous histamine-induced desensitization of the Ca2+ response in CHOhumH1 cells can be ascribed to an alteration at the level of the intracellular Ca2+ pool, as the Ca2+ response of caffeine (10 mM), which releases Ca2+ from intracellular Ca2+ stores was also attenuated upon short-term histamine exposure. 5. In CHOhumH1 cells the PKC activator, PMA, was found to inhibit the histamine (100 microM)-induced Ca2+ response concentration-dependently (IC50 0.2 +/- 0.03 microM) as well as the ATP (100 microM)-induced Ca2+ response. However, this inhibition was only partial and less effective than histamine-pretreatment. Moreover, in CHOhumH1 cells PKC downregulation induced by long-term exposure to PMA (1 microM) did not affect the histamine-induced desensitization nor did pretreatment with the specific PKC inhibitor Ro-31-8220 (10 microM), indicating that in CHOhumH1 cells PKC is probably not involved in the heterologous desensitization. 6. Long-term treatment of CHOhumH1 cells with histamine or other H1 agonists resulted in a time- and concentration-dependent decrease in the number of H1 receptor binding sites (maximal reduction: 47 +/- 5%). 7. Long-term exposure of CHOhumH1 cells to ATP or PMA did not affect H1 receptor density. 8. Both histamine (100 microM)- and ATP (100 microM)-induced Ca2+ responses were affected upon long-term exposure of cells to histamine (100 microM), which might be explained by an alteration at a level distant from the receptor. 9. These results show that in CHOhumH1 cells the human histamine H1 receptor is susceptible to short-term and long-term receptor regulation in which PKC does not seem to play a role. The CHOhumH1 cells therefore provide an excellent model system for studying the mechanism(s) of PKC-independent H1 receptor regulation.

Inhibitory effects of tetrandrine on intracellular free Ca2+ increase induced by glutamate, serotonin and histamine in dissociated retina cells

The effects of tetrandrine (Tet) on the elevation of intracellular free Ca2+ concentration ([Ca2+]i) induced by glutamate, serotonin and histamine in dissociated rabbit retina cells were studied. The changes of [Ca2+]i were reflected by the fluorescent indicator, Fura-2/AM, employed. In the presence of extracellular Ca2+ (1.3 mM), glutamate, serotonin and histamine significantly increased the [Ca2+]i in a dose-dependent manner. Glutamate (100 microM), serotonin (100 microM) and histamine (200 microM) markedly increased the [Ca2+]i of retina cells by 165%, 126% and 58%, respectively. Tet 30 microM significantly inhibited the increase of [Ca2+]i induced by glutamate (100 microM), serotonin (100 microM) and histamine (200 microM) by 28.0%, 46.8% and 29.0%, respectively. A lower concentration (10 microM) of Tet also produced an inhibitory effect on the increase of [Ca2+]i but was less effective than the Tet 30 microM. In Ca(2+)-free Hank's solution, Tet did not produce a significant inhibitory effect on the increase of [Ca2+]i caused by serotonin and histamine. These results indicate that Tet exercises blocking Ca2+ influx from the extracellular site via NMDA, 5-HT2 and H1-receptor operated Ca2+ channels and has no obvious effect on the Ca2+ release from intracellular Ca2+ stores.

Characteristics of the binding of [3H]-mepyramine to intact human U373 MG astrocytoma cells: evidence for histamine-induced H1-receptor internalisation

1. The kinetics of the binding of 5 nM [3H]-mepyramine to sites on intact human U373 MG astrocytoma cells, sensitive to inhibition by 2 microM pirdonium, were temperature-dependent. At 37 degrees C the half-time for association was 0.9 +/- 0.4 min and at 4 degrees C 19 +/- 3 min. Dissociation of bound [3H]-mepyramine was fast at 37 degrees C, t0.5 1.5 +/- 0.3 min, but at 6 degrees C dissociation initiated by dilution or addition of unlabelled mepyramine was negligible over 120 min. The very slow dissociation at 6 degrees C made it possible to reduce the level of pirdonium-insensitive binding from 56 +/- 5% to 39 +/- 5% by washing the cells in ice-cold medium before filtration. 2. The binding of [3H]-mepyramine sensitive to 2 microM temelastine, measured after 10 min equilibration at 37 degrees C, failed to saturate and was resolved into an hyperbola and an apparently linear component, whereas the fit to the binding of [3H]-mepyramine sensitive to 2 microM pirdonium was not significantly improved over that to an hyperbola. The mean Kd for the binding of [3H]-mepyramine to the saturable component, 2.5 +/- 0.4 nM, was in close agreement with the value of 3.5 nM for mepyramine derived from inhibition of histamine H1-receptor-mediated inositol phosphate formation in U373 MG cells. 3. Curves for the inhibition of the binding of 5 nM [3H]-mepyramine to U373 MG cells by histamine H1-receptor antagonists were biphasic and were fitted to a two site-model. Affinities calculated from the best-fit IC50 values for the high-affinity site correlated well with those expected for binding to H1-receptors. 4. The percentages of the high-affinity site in curves of the inhibition of [3H]-mepyramine binding to intact U373 MG cells by two tertiary amine antagonists, norpirdonium and 4-methyldiphenhydramine, 68 +/- 3 and 63 +/- 4%, were significantly greater than the percentages of the high-affinity site in the inhibition curves of their quaternary derivatives, 50 +/- 1 and 45 +/- 3%, respectively. Similarly, the percentage of the high-affinity site for unlabelled mepyramine, 65 +/- 7%, was greater than for the non-cell penetrant H1-antagonist temelastine, 42 +/- 5%. 5. Incubation of U373 MG cells with 100 microM histamine at 37 degrees C, followed by washing twice in ice-cold medium and then incubation with 1-15 nM [3H]-mepyramine for 120 min at 4 degrees C, resulted in a decrease in the binding of [3H]-mepyramine sensitive to 2 microM pirdonium, compared to control cells not exposed to histamine. The binding of [3H]-mepyramine in the absence of pirdonium was not altered by histamine pretreatment, whereas the level of the pirdonium-insensitive binding was significantly increased, except after 1 min exposure to histamine. The decreases in the pirdonium-sensitive binding after 5, 10 and 60 min incubation with 100 microM histamine were 41 +/- 6, 56 +/- 6 and 67 +/- 8%, respectively, but the decrease after 1 min incubation with histamine, 16 +/- 8%, was not statistically significant. 6. The results are consistent with the binding of [3H]-mepyramine to intact U373 MG cells being to both plasma membrane and intracellular histamine H1-receptors. The high-affinity binding sensitive to the non-cell penetrant quaternary compounds and to temelastine is thus to plasma membrane H1-receptors. On exposure to 100 microM histamine receptors are translocated to the intracellular pool, since the change in the high-affinity binding of [3H]-mepyramine is primarily in the level of the pirdonium-insensitive binding, rather than in the total binding.

Influence of histamine on the bradykinin response of canine testicular polymodal receptors in vitro

Effects of histamine on the testicular polymodal receptors were studied in vitro using canine testis-spermatic nerve preparations. Histamine induced distinct increase in the discharge rate in 6 out of 17 units tested (high responders), while it only weakly excited the remaining 11 units (low responders). The bradykinin response of low responders tended to be slightly facilitated by pretreatment with histamine, while that of high responders tended to be suppressed. Significant correlation was observed between the magnitude of histamine-induced discharges and the magnitude of change in the bradykinin responses.

Oscillations in cytosolic free Ca2+ induced by ADP and ATP in single rat hepatocytes display differential sensitivity to application of phorbol ester

We have previously described differences in the oscillatory responses of cytosolic free Ca2+ concentration ([Ca2+]i) in hepatocytes to ADP and ATP, which we have interpreted as evidence that these two nucleotides are acting at distinct receptors. We show here that ADP- and ATP-induced oscillations are differentially sensitive to application of the phorbol ester 4 beta-phorbol 12,13-dibutyrate (PDB). ADP-induced [Ca2+]i oscillations are abolished by low concentrations of PDB (5-10 nM), whereas ATP-induced oscillations of long duration are refractory to PDB, even at greatly elevated concentrations (100 nM). The data illustrate a further difference in the actions of ADP and ATP, strengthening the argument that these agonists are not acting at the same receptor on rat hepatocytes.

Activation of protein kinase C inhibits ATP-induced [Ca2+]i elevation in rat osteoblastic cells: selective effects on P2Y and P2U signaling pathways

Extracellular ATP elicits transient elevation of cytosolic free Ca2+ concentration ([Ca2+]i) in osteoblasts through interaction with more than one subtype of cell surface P2-purinoceptor. Elevation of [Ca2+]i arises, at least in part, by release of Ca2+ from intracellular stores. In the present study, we investigated the possible roles of protein kinase C (PKC) in regulating these signaling pathways. [Ca2+]i of indo-1-loaded UMR-106 osteoblastic cells was monitored by spectrofluorimetry. In the absence of extracellular Ca2+, ATP (100 microM) induced transient elevation of [Ca2+]i to a peak 57 +/- 7 nM above basal levels (31 +/- 2 nM, means +/- S.E.M., n = 25). Exposure of cells to the PKC activator 12-O-tetradecanoyl-beta-phorbol 13-acetate (TPA, 100 nM) for 2 min significantly reduced the amplitude of the ATP response to 13 +/- 4 nM (n = 11), without altering basal [Ca2+]i. Inhibition was half-maximal at approximately 1 nM TPA. The Ca2+ response to ATP was also inhibited by the PKC activators 1,2-dioctanoyl-sn-glycerol or 4 beta-phorbol 12,13-dibutyrate, but not by the control compounds 4 alpha-phorbol or 4 alpha-phorbol 12,13-didecanoate. Furthermore, exposure of cells to the protein kinase inhibitors H-7 or staurosporine for 10 min significantly attenuated the inhibitory effect of TPA. However, these protein kinase inhibitors did not prolong the [Ca2+]i response to ATP alone, indicating that activation of PKC does not account for the transient nature of this response. When the effects of other nucleotides were examined, TPA was found to cause significantly greater inhibition of the response to the P2Y-receptor agonists, ADP and 2-methylthioATP, than the response to the P2U-receptor agonist, UTP. These data indicate that activation of PKC selectively inhibits the P2Y signaling pathway in osteoblastic cells. In vivo, endocrine or paracrine factors, acting through PKC, may regulate the responsiveness of osteoblasts to extracellular nucleotides.

Agonist-induced desensitization of histamine H1 receptor-mediated inositol phospholipid hydrolysis in human umbilical vein endothelial cells

1. The regulation of histamine-induced [3H]-inositol phosphate formation was studied in human cultured umbilical vein endothelial cells (HUVEC). 2. Histamine (EC50 4.8 microM) produced a 12.7 fold increase in [3H]-inositol phosphate formation over basal levels. Prior exposure to 0.1 mM histamine (2 h) produced a 78% reduction in the response to subsequent histamine (0.1 mM) challenge. The IC50 for this histamine-induced desensitization was 0.9 microM. 3. The inositol phosphate response to histamine (0.1 mM) was inhibited by phorbol dibutyrate (IC50 40 nM; maximal reduction 64%). This effect was antagonized by both staurosporine (100 nM) and Ro 31-8220 (10 microM). However, the histamine-induced desensitization of the H1-receptor-mediated inositol phosphate response was insensitive to the protein kinase inhibitors, staurosporine, Ro 31-8220, K252a and KN62. 4. Prior exposure to sodium nitroprusside (100 microM), forskolin (10 microM) or dibutyryl cyclic AMP (1 mM) had no effect upon histamine-induced [3H]-inositol phosphate formation. 5. NaF (20 mM) and thrombin (EC50 0.4 u ml-1) also induced inositol phosphate formation in HUVEC. Histamine pretreatment (0.1 mM, 10-120 min) failed to modify the inositol phosphate response to a subsequent NaF or thrombin challenge. 6. We conclude that the desensitization of histamine H1-receptor-mediated [3H]-inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activation of protein kinase A, G, or C, or calcium calmodulin-dependent protein kinase II.