Two B1 and B2 bradykinin receptor antagonists fail to inhibit the Ca2+ response elicited by bradykinin in human skin fibroblasts

The elevation of intracellular [Ca2+] induced by bradykinin (Bk) was monitored with fura-2 fluorescence in human skin fibroblasts. Neither [des-Arg10][Leu9]kallidin nor D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE140) inhibited the Ca2+ response stimulated by Bk. Moreover, each behaved as a partial agonist causing the elevation of intracellular [Ca2+].     

Differential regulation of Ca(2+)-dependent Cl- currents by FP prostanoid receptor isoforms in Xenopus oocytes

The FP(A) and FP(B) prostanoid receptor isoforms are G-protein-coupled receptors that are activated by prostaglandin F(2alpha) (PGF(2alpha)). Differences in their carboxyl termini prompted us to examine the intracellular calcium (Ca(2+)) signaling of these receptor isoforms using the Xenopus oocyte expression system. Protein expression was determined by immunofluorescence microscopy and whole cell binding with [3H]PGF(2alpha). Positive immunolabeling was observed on the outer membranes of oocytes expressing FLAG-tagged FP receptor isoforms, but not on control (water-injected) oocytes. Intracellular signaling was examined using a two-electrode voltage clamp. Specific whole-cell binding was also detected for both receptor isoforms. Bath application of 10 microM PGF(2alpha) to FP(A)-expressing oocytes produced a chloride (Cl-) current response similar to that of an injection of inositol 1,4,5-trisphosphate (InsP(3)) (5.76+/-0.6 microA, peak current; N=23) that returned to control levels within 25 min. In FP(B)-expressing oocytes the activation of the Cl- current was delayed or completely absent (1.38+/-0.2 microA, peak current; N=18). Control oocytes were not responsive to the application of PGF(2alpha) (0.87+/-0.1 microA, peak current; N=10). Activation of Cl- currents for both FP receptor isoforms was dependent upon intracellular Ca(2+) stores as a 30-min pretreatment with thapsigargin (1 microM; N=5) blocked the PGF(2alpha) induction of the Cl- current. These data indicate that the FP prostanoid receptor isoforms differ in their ability to activate Ca(2+)-dependent Cl- channels when expressed in Xenopus oocytes. The difference appears to be in the ability of the two FP prostanoid receptor isoforms to mobilize intracellular calcium.     

Effects of specific prostanoid EP receptor agonists on cell proliferation and intracellular Ca concentrations in human airway smooth muscle cells

Increased airway smooth muscle mass due to cell proliferation contributes to airway hyper-responsiveness and remodeling in patients with asthma. Prostaglandin E₂ (PGE₂) inhibits proliferation of airway smooth muscle cells, but the role of prostanoid EP receptor subtypes in mechanisms involved has not been fully elucidated yet. We investigated the effects of specific prostanoid EP receptor agonists on cell proliferation and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in human airway smooth muscle cells. Cell numbers were assessed by mitochondria-dependent reduction of 4-[3-(4-lodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1, 3-benzene disulfonate to formazan (WST-1 assay). RT-PCR data showed that human airway smooth muscle cells express EP2, EP3, and EP4 but not EP1 receptor mRNA. PGE₂ (1 nM–1 μM) inhibited cell proliferation induced by 5% fetal bovine serum (FBS) in a concentration-dependent manner. (16S)-9-deoxy-9β-chloro-15-deoxy-16-hydroxy-17, 17-trimethylene-19, 20-didehydro PGE₂ sodium salt (ONO-AE1-259-01; EP2 receptor agonist) and 16-(3-methoxymethyl)phenyl-ω-tetranor-3,7-dithia PGE₂ (ONO-AE1-329; EP4 receptor agonist) inhibited the 5% FBS-induced cell proliferation. ONO-AE1-259-01 and ONO-AE1-329 also significantly increased the cytosolic cAMP levels. In contrast, 11,15-O-dimethyl PGE₂ (ONO-AE-248; EP3 receptor agonist) elicited an oscillatory increase in [Ca²⁺]_i but did not affect the cell growth or cAMP levels. [(17S)-2,5-ethano-6-oxo-17,20-dimethyl PGE₁] (ONO-DI-004; EP1 receptor agonist) did not affect cell growth, cAMP levels, or [Ca²⁺]_i. In conclusion, PGE₂ inhibits FBS-induced cell proliferation mostly via EP2 and EP4 receptor activation and subsequent cAMP elevation. The EP3 receptor agonist causes an increase in [Ca²⁺]_i without affecting cell growth. There is no functional expression of the EP1 receptor. Research on prostanoid EP receptors may lead to novel therapeutic strategies for treatment of asthma.     

癫痫发作过程中细胞内钙、一氧化氮合酶与细胞凋亡的关系

目的 探讨癫痫发作过程中神经细胞内钙、一氧化氮合酶(NOS)与细胞凋亡的关系.方法 采用戊四氮(PTZ)致痫大鼠模型,分为对照组,致痫后30 min、1、3、6、12、24、48 h组,每组8只.流式细胞术检测细胞内钙和细胞凋亡,紫外分光光度计检测NOS.结果 对照组钙水平较低,癫痫发作后钙迅速升高,1 h达高峰,之后下降;NOS在癫痫发作后1、24 h有2个分泌高峰,与对照组比较差异有统计学意义(P<0.05);细胞凋亡在癫痫发作后6 h开始升高,24 h达高峰,与对照组比较有显著性差异(P<0.05).结论 钙超载和NOS过度表达可能与癫痫后的细胞凋亡有关.     

Differential regulation of the signaling and trafficking of the two prostaglandin D2 receptors, prostanoid DP receptor and CRTH2

Prostaglandin D2 (PGD2) exerts its actions on two G protein-coupled receptors, the prostanoid DP receptor and CRTH2 (chemoattractant homologous receptor expressed on TH2 cells). Here, we characterize the regulation of the signaling and trafficking of the prostanoid DP receptor and CRTH2. Time-course and dose-response curves showed that both receptors expressed in HEK293 cells internalized maximally after 2 h of stimulation with 1 microM PGD2. Co-expression of the G protein-coupled receptor kinases GRK2, GRK5 or GRK6 increased agonist-induced internalization of CRTH2, while only GRK2 had an effect on the internalization of the prostanoid DP receptor. Protein kinase C (PKC) activation stimulated the internalization of both receptors. Interestingly, only PGD2-induced internalization of CRTH2, and not of prostanoid DP receptor, was decreased by inhibition of PKC or protein kinase A (PKA). Our data also indicate that CRTH2 is subjected to basal phosphorylation by PKA, which appears to be involved in CRTH2 internalization. Prostanoid DP receptor internalization was promoted by co-expression of arrestin-2 and -3, while the internalization of CRTH2 was increased by co-expression of arrestin-3 only. The detection of prostanoid DP receptor and CRTH2 internalization was reduced by the co-expression of Rab4 and Rab11, respectively, suggesting differential regulation of receptor recycling. Moreover, immunofluorescence microscopy experiments showed that the prostanoid DP receptor specifically co-localized with Rab4, and CRTH2 with Rab11. The signaling of the prostanoid DP receptor was regulated by GRK2 overexpression, while that of CRTH2 was modulated by overexpression of GRK2, -5 and -6. Our results show a differential regulation of the prostanoid DP receptor and CRTH2, two receptors for PGD2.     

Biphasic regulation of the gonadotropin-releasing hormone receptor by receptor microaggregation and intracellular Ca2+ levels

In the present work we show that Ca2+ is both necessary and sufficient to evoke homologous up-regulation of the gonadotropin-releasing hormone (GnRH) receptor. Extracellular Ca2+ as well as RNA and protein synthesis were required for this event, and it was blocked by Ca2+ ion channel blockers. Drugs which stimulated increased intracellular Ca2+ levels also stimulated receptor up-regulation and enhanced responsiveness even in the absence of added GnRH. Such drugs were effective below the concentrations needed to evoke luteinizing hormone (LH) release, suggesting that enhanced levels of Ca2+ ion, rather than LH depletion, is the responsible agent. A GnRH antagonist did not evoke up- or down-regulation; however, a conjugate of this antagonist, which stimulated microaggregation of the GnRH receptor, also stimulated these biphasic actions. In contrast to up-regulation, down-regulation of the GnRH receptor appears to be Ca2+-independent and does not require RNA or protein synthesis. These data are consistent with a model in which microaggregation of the GnRH receptor is the final step in common to a branched pathway consisting of Ca2+-dependent (LH release, enhanced sensitivity, up-regulation) and Ca2+-independent (desensitization, down-regulation) events.     

Expression of both alpha 1- and alpha 2-adrenoceptors in an insulin-secreting cell line. Parallel studies of cytosolic free Ca2+ and insulin release

Changes in intracellular free Ca2+, [Ca2+]i, and immunoreactive insulin release in response to alpha-adrenergic agents were measured in RINm5F cell suspensions. Cells were loaded with the fluorescent indicator quin 2 for monitoring [Ca2+]i. Epinephrine (1 microM), which inhibited alanine-stimulated insulin release by 73%, evoked a transient rise in [Ca2+]i. This rise is in part due to Ca2+ mobilization, since it is still present in the absence of extracellular Ca2+. The alpha 2-adrenergic agonist clonidine (10 microM) mimicked the epinephrine effect on insulin release without any change in [Ca2+]i. In contrast, the alpha 1-adrenergic agonist phenylephrine (10 and 100 microM) raised [Ca2+]i, albeit to a lesser extent than epinephrine. Phenylephrine enhanced basal, but had no effect on alanine-stimulated insulin release. To examine further the nature of the effect of epinephrine, specific alpha-adrenergic blocking agents were employed. The epinephrine-induced increase in [Ca2+]i could be inhibited by the alpha 1-adrenergic antagonists BE2254 (0.1 microM) and prazosin (0.01 microM). In the presence of these blockers, epinephrine was still able to inhibit insulin release. When alpha 2-adrenergic receptors were blocked by the addition of idazoxan (0.1 and 1 microM), epinephrine still raised [Ca2+]i. At the higher concentration of idazoxan, the epinephrine inhibition of insulin release was completely overcome. The alpha-adrenergic agonists did not attenuate the alanine-induced rise in [Ca2+]i. This study shows that both subtypes of alpha-adrenergic receptors are present in the insulin-secreting cell line RINm5F. The activation of alpha 1-adrenergic receptors leads to an increase in [Ca2+]i. In contrast, the inhibition of insulin release due to epinephrine is mediated through alpha 2-adrenergic receptors. The alpha 2-adrenergic mechanism does not involve changes in [Ca2+]i, but is rather exerted at a later step in the secretory process.     

Design and synthesis of novel sulfonamide-containing bradykinin hB2 receptor antagonists. 1. Synthesis and SAR of alpha,alpha-dimethylglycine sulfonamides

We recently published the extensive in vivo pharmacological characterization of MEN 16132 (J. Pharmacol. Exp. Ther. 2005, 616-623; Eur. J. Pharmacol. 2005, 528, 7), a member of the sulfonamide-containing human B(2) receptor (hB(2)R) antagonists. Here we report, in detail, how this family of compounds was designed, synthesized, and optimized to provide a group of products with subnanomolar affinity for the hB(2)R and high in vivo potency after topical administration to the respiratory tract. The series was designed on the basis of indications from the X-ray structures of the key structural motifs A and B present in known antagonists and is characterized by the presence of an alpha,alpha-dialkyl amino acid. The first lead (17) of the series was submitted to extensive chemical work to elucidate the structural requirements to increase hB(2) receptor affinity and antagonist potency in bioassays expressing the human B(2) receptor (hB(2)R). The following structural features were selected: a 2,4-dimethylquinoline moiety and a piperazine linker acylated with a basic amino acid. The representative lead compound 68 inhibited the specific binding of [(3)H]BK to hB(2)R with a pKi of 9.4 and antagonized the BK-induced inositolphosphate (IP) accumulation in recombinant cell systems expressing the hB(2)R with a pA(2) of 9.1. Moreover, compound 68 when administered (300 nmol/kg) intratracheally in the anesthetized guinea pig, was able to significantly inhibit BK-induced bronchoconstriction for up to 120 min after its administration, while having a lower and shorter lasting effect on hypotension.     

Role of endoplasmic reticulum, an intracellular Ca2+ store, in histamine release from rat peritoneal mast cell.

By means of the Ca-antimonate precipitation technique, it was revealed that Ca2+ accumulates in the endoplasmic reticulum (ER) of rat peritoneal mast cells. The ER of rat mast cells was isolated using Percoll density gradient centrifugation, and its characteristics were studied. Although the uptake of 45Ca into the ER was enhanced by adenosine 5'-triphosphate (ATP) at concentrations lower than 2 mM, at higher concentrations ATP induced 45Ca release from the ER, suggesting that bidirectional translocation of Ca2+ takes place in the ER membrane. When apyrase was added to the reaction mixture to decompose all ATP molecules, the amount of 45Ca in the ER was decreased, indicating that ATP is necessary to retain Ca2+ in the ER. Not only inositol 1,4,5-trisphosphate (IP3) but also guanosine 5'-triphosphate (GTP) was effective in releasing Ca2+ from the ER at concentrations higher than 2 microM, while guanosine 5'-[gamma-thio]-triphosphate (GTP-gamma S), a non-hydrolysable analogue of GTP, was not effective. This may indicate that a hydrolysis of GTP is necessary for Ca2+ release from the ER. Intracellular Ca2+ blockers such as 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) and dantrolene sodium were effective in inhibiting Ca2+ release from ER induced by IP3. The Ca2+ release due to IP3 was also inhibited by flunarizine, a Ca2+ channel blocker, and by oxatomide, an antiallergic drug. Since these two compounds are diphenylpiperazine derivatives, it is suggested that a diphenylpiperazine moiety may be effective in inhibiting Ca2+ release from the ER.     

Involvement of Ca(2+)-induced Ca2+ releasing system in interleukin-1beta-associated adenosine release

Interleukin-1beta (IL-1beta) plays an important role in neuroprotective and neurodegenerative events in the central nervous system. To clarify the mechanism of controversial actions of IL-1beta, we determined the effect of IL-1beta, as well as the interaction between IL-1beta and Ca(2+)-induced Ca2+ releasing system (CICR), on adenosine releases in mice hippocampus using mini-slices method. Basal and K(+)-stimulated adenosine releases were regulated by two types of CICRs, including inositol-1,4,5-trisphosphate (IP3) receptor and ryanodine receptor. Lower concentration of IL-1beta increased both adenosine releases, whereas higher concentration did not affect their releases. The stimulatory effect of IL-1beta on basal adenosine release was reduced by removal of extracellular Ca2+ and IP3 receptor inhibitor, while the stimulatory effect of IL-1beta on K(+)-stimulated adenosine release was reduced by ryanodine receptor inhibitor. These results suggest that the potent effect of IL-1beta upon adenosine release might contribute to the neuroprotective action of IL-1beta, whereas IL-1beta-induced neurodegeneration might be due to the overload response of Ca2+ mobilization and the inactivation of adenosine exocytosis.     

蝙蝠葛苏林碱对心肌细胞浆Ca~（2＋）活度的影响

目的：探讨蝙蝠葛苏林碱（ＤＳ）对迟后除极的作用．方法：采用Ｃａ２＋敏感性微电极技术．结果：毒毛旋花甙Ｇ（Ｓｔｒ，３μｍｏｌ·Ｌ－１）使豚鼠心室乳头肌细胞浆Ｃａ２＋活度（ɑｉＣａ）增加０１９±０１１μｍｏｌ·Ｌ－１，在出现迟后除极和触发活动（ＴＡ）时又分别增加１４８±０５５和４９６±１８１μｍｏｌ·Ｌ－１．标本经ＤＳ作用后．Ｓｔｒ不再引起ɑｉＣａ增高和ＴＡ．ＤＳ抑制无Ｎａ＋和咖啡因引起的狗心肌ɑｉＣａ增加．结论：ＤＳ可阻止Ｃａ２＋跨膜入胞浆而防止ɑｉＣａ增高起抗ＴＡ作用．     

Autoregulation of bradykinin receptors: agonists in the presence of interleukin-1beta shift the repertoire of receptor subtypes from B2 to B1 in human lung fibroblasts.

Elevated formation of bradykinin (BK) and Lys-BK or kallidin (KD) and their carboxypeptidase metabolites desArg(9)BK and desArg(10)KD is evident at sites of inflammation. Moreover, B2 receptors (B2R), which mediate the action of BK and KD, participates in the acute stage of the inflammatory and pain response, whereas B1 receptors (B1R), through which desArg(9)BK and desArg(10)KD act, partake in the chronic stage. We hypothesized that kinins autoregulate B2R and B1R expression in favor of B1R. Incubation of IMR-90 cells with BK (100 nM) led to a loss (89%) of B2R with a half-life (T(1/2)) of 7.0 min. Concomitantly, BK increased B1R (2- to 3-fold) with a T(1/2) of 120 min. DesArg(10)KD (100 nM) had no effect on B2R but increased B1R (3- to 4-fold) with the same rate as BK. Interleukin-1beta (IL-1beta; 500 pg/ml) also increased B1R (4- to 6-fold). Although both desArg(10)KD and BK increased the level of IL-1beta mRNA, IL-1beta receptor antagonist inhibited the increase in B1R only in response to BK. DesArg(10)KD and BK synergistically increased B1R (9-fold), which was further increased by inclusion of IL-1beta (36-fold). Therefore, kinin metabolism and kinin-stimulated production of cytokines may play a pivotal role in shifting the repertoire of kinin receptor subtypes in favor of B1R during inflammation.     

Ca2+ release induced by myotoxin alpha, a radio-labellable probe having novel Ca2+ release properties in sarcoplasmic reticulum.

1. Myotoxin alpha (MYTX), a polypeptide toxin purified from the venom of prairie rattlesnakes (Crotalus viridis viridis) induced Ca2+ release from the heavy fraction (HSR) but not the light fraction of skeletal sarcoplasmic reticulum at concentrations higher than 1 microM, followed by spontaneous Ca2+ reuptake by measuring extravesicular Ca2+ concentrations using the Ca2+ electrode. 2. The rate of 45Ca2+ release from HSR vesicles was markedly accelerated by MYTX in a concentration-dependent manner in the range of concentrations between 30 nM and 10 microM, indicating the most potent Ca2+ releaser in HSR. 3. The Ca2+ dependency of MYTX-induced 45Ca2+ release has a bell-shaped profile but it was quite different from that of caffeine, an inducer of Ca(2+)-induced Ca2+ release. 4. 45Ca2+ release induced by MYTX was remarkable in the range of pCa between 8 and 3, whereas that by caffeine was prominent in the range of pCa, i.e., between 7 and 5.5. 5. MYTX-induced 45Ca2+ release consists of both early and late components. The early component caused by MYTX at low concentrations (30-300 nM) completed within 20 s, while the late component induced by it at higher concentrations (> 0.3 microM) was maintained for at least 1 min. 6. Both the components were almost completely inhibited by inhibitors of Ca2+ such as Mg2+, ruthenium red and spermine. 7. 45Ca2+ release induced by caffeine or beta,gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) was completely inhibited by high concentrations of procaine. Procaine abolished the early component but not the late one, suggesting that at least the early component is mediated through Ca(2+)-induced Ca2+ release channels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of sphingosine-1-phosphate and sphingosylphosphorylcholine on intracellular Ca2+ and cell death in prostate cancer cell lines

The sphingolipid metabolites sphingosine-1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) can be involved in cellular growth and apoptosis, by both receptor-dependent and -independent mechanisms. We investigated the role of S1P and SPC in intracellular Ca2+ elevation, cell proliferation and cell death in DU 145 and PC3 hormone-refractory prostate cancer cell lines. S1P and SPC increased intracellular Ca2+ levels, most likely in a receptor-independent manner. Surprisingly, both S1P and SPC did not stimulate but rather reduced cell growth through induction of apoptosis. Therefore, antagonists targeted against S1P, SPC and their receptors do not appear to be promising new approaches in the treatment of hormone-refractory prostate cancer.     

Agonist-mediated regulation of alpha 1- and beta 2-adrenergic receptor metabolism in a muscle cell line, BC3H-1

We have compared the metabolism of alpha 1- and beta 2-adrenergic receptors which are both expressed in BC3H-1 muscle cells. During growth of the cells to confluence, the number of alpha 1-receptors per mg of membrane protein increases, whereas that of the beta 2-receptors remains constant. Experiments using cycloheximide and irreversible alpha 1- and beta 2-receptor antagonists, phenoxybenzamine and N-[2-hydroxy-3-(1-naphthoxy)-propyl]-N'-bromoacetylethylenediamine , respectively, yield disparate turnover rates (t1/2) for the two receptors: alpha 1 congruent to 25 hr, beta 2 congruent to 200 hr. These experiments suggest that synthesis of beta 2-receptors virtually ceases in confluent cells. Maximally effective doses of agonists down-regulated both receptor types 80-90% and enhanced the rates of loss of both receptors (t1/2 = 1-5 hr). The rates of down-regulation were not affected by cycloheximide, implying that agonists enhance receptor clearance rather than decrease receptor appearance. The rank orders of potencies of agonists for promoting receptor down-regulation were those characteristic of alpha 1- and beta 2-receptors. However, concentrations of agonists that resulted in down-regulation of each receptor subtype were 10- to 100-fold lower than those required for occupancy of receptors as assessed in radioligand binding studies. Receptor recovery following removal of agonists was blocked by cycloheximide and was much faster than the recovery that followed treatment of cells with irreversible antagonists. Therefore, protein synthesis (but perhaps not receptor synthesis per se) appears necessary for recovery from down-regulation. In addition, the rates of recovery of alpha 1- and beta 2-receptor-mediated functions (phosphatidylinositol turnover and cyclic AMP synthesis, respectively) following receptor down-regulation or irreversible blockade parallel the rates of receptor recovery. These data indicate that basal metabolism of alpha 1- and beta 2-receptors in BC3H-1 cells is substantially different, but that agonist-mediated changes in metabolism of the two receptor subtypes are similar. Thus, common mechanisms appear to mediate the regulation by agonists of alpha 1- and beta 2-receptors in these cells.     

Novel effects mediated by bradykinin and pharmacological characterization of bradykinin B2 receptor antagonism in human synovial fibroblasts

Background and purpose:

Bradykinin (BK) and B₂ receptors have been implicated in the pathophysiology of osteoarthritis (OA), and synovitis is one of its hallmarks. Here, the selective B₂ receptor antagonists MEN16132 and icatibant have been pharmacologically characterized in human synovial cells.

Experimental approach:

Radioligand and functional studies (inositol phosphate (IP) accumulation, interleukin (IL)-6 and IL-8 release) were performed in cultured synoviocytes.

Key results:

[³H]-BK saturation studies indicated receptor density (B_max) and K_d values of 121 550 sites per cell and 1.14 nM respectively. In synoviocytes, MEN16132 (pK_i 8.9) was threefold more potent than icatibant (pK_i 8.4). Both antagonists showed competitive antagonism in the BK-induced IP assay (control EC₅₀ 0.45 nM), with pK_B values of 9.9 (MEN16132) and 8.1 (icatibant). 24h incubation with BK induced IL-6 (EC₅₀ 216 nM) and IL-8 (EC₅₀ 53 nM) release. Both MEN16132 (IL-6: pIC₅₀ 8.1; IL-8: pIC₅₀ 8.4) and icatibant (IL-6: pIC₅₀ 6.6; IL-8: pIC₅₀ 6.7) completely prevented this BK-induced release. Indomethacin did not affect the basal or the IL-6/IL-8 release induced by BK, whereas nordihydroguaiaretic acid decreased the basal release, although BK still increased IL-6 and IL-8 production. BK-induced IL-8 release was attenuated by inhibitors of phospholipase C ({"type":"entrez-nucleotide","attrs":{"text":"U73122","term_id":"4098075","term_text":"U73122"}}U73122), p38 (SB203580), JNK (SP600125), ERK 1/2 (PD98059) MAPKs, phosphoinositide 3-kinase ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002), NF-κb (BAY-117085) and by the glucocorticoid dexamethasone.

Conclusions and implications:

Bradykinin via B₂ receptors can participate in inflammatory events in synovitis. MEN16132 is a highly potent B₂ receptor antagonist capable of blocking pro-inflammatory responses to BK evoked in human synoviocytes.     

Dopamine induces intracellular Ca2+ signals mediated by alpha1B-adrenoceptors in rat pineal cells.

We have studied the functional interaction of dopamine with alpha1-adrenoceptor subtypes by measuring intracellular Ca2+ levels in pineal cells, a cell type where adrenoceptors are well characterized. We show that dopamine induces transient intracellular Ca2+ signals in only 70% of cells responding to phenylephrine. Dopamine-induced Ca2+ signals desensitise faster than Ca2+ transients elicited with phenylephrine and are selectively blocked by desipramine, imipramine, and alpha1B-adrenoceptor antagonists. These results suggest that dopamine induced Ca2+ signals are mainly due to the activation of one subtype of alpha-adrenoceptor, the alpha1B.