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At least 847 records · Page 47Linked to original sources
PubMed1984

Leukotriene D4 elicits a non-sustained contraction of the guinea pig trachea in calcium-free buffer.

The contraction of the isolated guinea pig trachea elicited by leukotriene D4 (LTD4) in Ca2+-free buffer (containing 10(-4) M EGTA) achieved a maximum at 6-8 min and relaxed back to baseline approximately 25 min after challenge with LTD4. In contrast, LTD4 elicited a sustained contraction in the presence of 1.8 mM calcium. This sustained contraction in the presence of calcium was reproduced upon repeated LTD4 challenge, whereas in Ca2+-free buffer, only one LTD4-induced contraction could be obtained. The amplitude of the LTD4-induced contraction in Ca2+-free buffer decreased in a time-dependent manner which was also dependent upon the concentration of LTD4. At 10(-7) and 10(-6) M LTD4, small contractions (11% and 20% of control, respectively) were measured after 30 min in Ca2+-free buffer, whereas 10(-8) M LTD4 elicited a contraction at 15 min but not after 30 min in Ca2+-free buffer. Whereas washing the trachea for 5 min with LaCl3 (1.8 mM) only partially suppressed the LTD4-induced contraction in the presence of calcium, the contraction elicited by LTD4 in Ca2+-free buffer was not affected by LaCl3. The LTD4-induced contraction in Ca2+-free buffer was not affected by verapamil (10(-6) M); in contrast, the putative intracellular calcium antagonist, TMB-8 (10(-4) M), blocked the LTD4-induced contraction. These results provide evidence that the release of an intracellular calcium store plays an important role in the initiation of the LTD4-induced contraction of the guinea pig trachea. In addition, these results suggest that an extracellular calcium source may account for a small part of the LTD4-induced contraction.

Airway Resistance↗
PubMed1984

Role of calcium in arachidonic acid-induced contractions of guinea pig airways.

We have previously shown that arachidonic acid (AA)-induced contractions of indomethacin-pretreated guinea pig trachea and parenchyma are due to the synthesis of leukotrienes C4 and D4. The present experiments were designed to investigate the role of calcium (Ca2+) in the above. AA (66 microM)-induced contractions of trachea, but not parenchyma, were reduced in Ca2+-free Krebs-Henseleit solution ( KHS ). However the contractions of both trachea and parenchyma were abolished in Ca2+-free KHS with either lanthanum chloride (1 mM) or EDTA (300 microM). The Ca2+ antagonists, verapamil (100 microM), nitrendipine (100 microM), and TMB-8 (100 microM), reduced AA-induced contractions of both trachea and parenchyma. Re-addition of Ca2+ (2.2 mM) to trachea and parenchyma in Ca2+-free KHS in the presence of lanthanum restored the AA-induced contractions. This effect of Ca2+ was reduced by verapamil (100 microM) or nitrendipine (100 microM). LTC4-induced contractions of trachea and parenchyma were unaffected by nitrendipine (100 microM), whereas tracheal contractions were reduced in Ca2+-free KHS . Both tracheal and parenchymal contractions to LTC4 were reduced in Ca2+-free KHS in the presence of lanthanum chloride (1 mM). We conclude that superficially bound pools of Ca2+ are important in AA-induced contractions of the airways. Furthermore, nitrendipine reduces AA-induced contractions by inhibiting AA metabolism and not by inhibiting airway smooth muscle contraction induced by released leukotrienes.

Animals↗
PubMed1988

Allergic responses and subsequent development of airway hyperreactivity to cold provocation in the rat trachea: pharmacological modulation.

An in vitro model of airway hyperreactivity to cold provocation was developed. Cold provocation (10 degrees C) alone was not sufficient to cause contraction of rat isolated tracheal smooth muscle preparations. However, following recovery from antigen-induced responses in sensitized rat tracheal segments, cold provocation resulted in marked contractile responses. L-652,731 (a Paf-acether antagonist) and atropine significantly attenuated antigen-induced responses and subsequent development of airway hyperreactivity to cold provocation. Indomethacin augmented allergic responses and subsequent development of airway hyperreactivity to cold challenge. Nordihydroguaiaretic acid, FPL 55712 and theophylline did not exert any effect. The data obtained in this study showed that (i) Paf-acether and acetylcholine may play an important role in the mediation of allergic responses and subsequent development of airway hyperreactivity to cold provocation; (ii) the significant attenuation of antigen-induced airway hyperreactivity to cold provocation by Ca2+ channel blockers (nifedipine, bepridil and TMB-8) suggests an increase in Ca2+ influx/permeability following antigen challenge which appears to be responsible for the development of airway hyperreactivity to cold provocation; and (iii) 5-HT, prostaglandins or thromboxanes and leukotrienes play little or no role in the mediation of allergic responses and subsequent development of airway hyperreactivity to cold exposure in rat trachea.

Acetylcholine↗
PubMed1989

Calcium influx and protein kinase C activation involved in uterine vasoconstriction in guinea pigs.

The mechanical responses of circular segments of uterine arteries to different combinations of vasoactive agents and putative inhibitors of calcium fluxes were examined using a sensitive in vitro method. Exposure to high potassium (127 mM) or to noradrenaline (NA; 0.1 mM) resulted in a rapid, initial increase in tension of the vascular preparation to reach a sustained level of contraction (approximatively 12 mN) which lasted for at least 15 min. The protein kinase C activator, 4-beta-phorbol-12,13-esther-dibutyrate (10 microM), induced a slowly developing but sustained contractile response with a maximum (PDBumax) of only 4 mN. Addition of the calcium ionophore, A23187, to PDBu-contracted vessels did not increase tension, while the maximum tension evoked by A23187 per se (3 microM) was 5 mN. Ionomycin had only a small contractile effect on the uterine artery. The contraction evoked by depolarization (potassium) or alpha 1-adrenoceptor stimulation (NA) was decreased in nominally calcium-free medium containing EDTA (0-100 microM) or EGTA, while uterine arteries loaded intracellularly with the calcium chelator, quin-2, responded to the vasoconstrictors almost as well as the control preparations. Blockade of calcium influx with Cd2+ (greater than 0.01 mM), nifedipine (greater than 3 microM), verapamil (greater than 1 microM) and TMB-8 (greater than 10 microM) reduced the tension evoked by potassium somewhat more than it reduced the contractions induced by NA, while the opposite was seen in the presence of Ni2+ (greater than 0.1 mM). Inhibition of calmodulin-dependent enzymes by W7 (greater than 10 microM) reduced the maximum tension evoked by potassium and NA to a similar extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Interactions between oxytocin- and calcium-modifying agents in the rat testicular capsule in vitro.

We have studied the effect of drugs which affect the movement of calcium on the contractions induced by 50 and 200 nM oxytocin in the isolated testicular capsule of the rat. The ED50 for oxytocin in this preparation was 188 (+/- 66 S.E.) nM and the maximal contraction induced by oxytocin was smaller than that obtained with 10 microM of the calcium ionophore, A23187. Lanthanum (10 mM), cobalt (2 mM), EGTA (3.5 and 5 nM, 30 s exposure) and a decrease in the calcium concentration of the medium reduced the oxytocin response. The response was completely abolished after prolonged incubation with EGTA (2 mM) in a calcium-free medium. The calcium blocking agents, nifedipine and flunarizine, and the agonist, Bay K 8644, did not modify the responses to oxytocin. Verapamil, at possibly non-specific doses (10 microM), reduced the contractions while diltiazem (0.1 mM), in a prazosin (10 microM)-resistant way, and nickel (0.1 mM) increased them. Both modifiers of intracellular calcium that were used namely TMB-8 (10 microM), in a calcium-free medium, and dantrolene sodium (10 and 30 microM), with and without calcium in the medium, decreased the oxytocin response. On the whole, it seems as if both intra- and extracellular calcium were involved in the contractile effect of oxytocin, although extracellular calcium does not seem to gain access to the cell through voltage-dependent calcium channels sensitive to selective calcium entry blockers.

Animals↗
PubMed1989

Muscarinic stimulation of prostanoid synthesis by the isolated rat trachea: calcium dependency and effect of cortisol and cigarette smoke.

Tracheal prostanoid synthesis was stimulated by parasympathomimetics: arecoline greater than carbachol = methacholine greater than acetylcholine much greater than arecaidine. McNA343, dimethyl phenyl piperazinium (DMPP), nicotine, potassium and isoprenaline were without effect. Prostanoid synthesis was also stimulated by Ca2+ ionophore A23187 and arachidonic acid (AA). Carbachol-stimulated prostanoid synthesis was inhibited by cholinergic antagonists (atropine greater than ipratropium bromide much greater than gallamine greater than pirenzepine); adrenaline and isoprenaline were without effect. Carbachol-stimulated prostanoid synthesis was also inhibited by the Ca2+-channel blockers, nifedipine, diethylstilboestrol and TMB-8. Hydrocortisone and betamethasone inhibited carbachol- and A23187-stimulated, but not AA-stimulated, prostanoid synthesis following an 18 h tissue culture. Cigarette smoke extracts had a biphasic effect on carbachol-, A23187- and AA-stimulated prostanoid synthesis (potentiation at low concentrations, inhibition at high concentrations of extracts). These data demonstrate (1) that rat tracheal prostanoid synthesis is stimulable by activation of muscarine receptor-linked Ca2+ mobilisation, and (2) that tracheal prostanoid synthesis may be involved in secretion of mucus, the disruption of which by cigarette smoking may be related to the pathophysiology of airway disease.

Acetylcholine↗
PubMed1990

Distinct stimulatory effect of platelet-activating factor on prostaglandin I2 and thromboxane A2 biosynthesis by rat dental pulp.

Platelet-activating factor (PAF-acether), but not lyso PAF, stimulated the production of both PGI2 and TXA2 by rat dental pulp tissue in vitro. However, there were differences in the dose- and time-dependence of the stimulatory effects. PAF-acether antagonists, Bn 52021, CV 3988 and kadsurenone, dose dependently inhibited PAF-acether-induced PG production. BN 52021, CV 3988 also dose dependently inhibited TX production, but kadsurenone was almost without effect on TX production. Pretreatment of the tissues with PAF-acether or phorbol 12-myristate 13-acetate completely abolished the effect of the second challenge with PAF-acether. The stimulatory effects of PAF-acether and the calcium ionophore A23187 on PGI2 production were completely blocked by removal of extracellular calcium, whereas the effects on TXA2 production were not. TMB-8, an intracellular calcium antagonist, completely inhibited PAF-acether-induced PG production, whereas it slightly inhibited TX production. H-7, a protein kinase C inhibitor, and neomycin, a phospholipase C inhibitor, completely inhibited PAF-acether-induced PG and TX production, whereas W-7, a calmodulin inhibitor, did not. These results suggest that PAF-acether stimulates PGI2 and TXA2 production in rat dental pulp by interacting with distinct PAF-acether receptors, and that these receptors are coupled to independent signal transduction pathways which have a different dependence on extra- and intracellular calcium.

Animals↗
PubMed1992

Mechanism of contractile responses to bradykinin in canine basilar arteries.

This study was undertaken to investigate the role of endothelium in the modulation of vascular responses to bradykinin and to elucidate the receptor types and mechanism of action of bradykinin in isolated basilar artery. The results showed a contractile response to bradykinin in basilar artery. This contractile response to bradykinin was partially modulated by endothelium in a dose-dependent manner. In addition, both des-Arg9-[Leu8]bradykinin and [d-Arg0,Hyp3,Thi5,8,D-Phe7]bradykinin significantly antagonized the responses to bradykinin. However, the blocking effect and the apparent affinity of [d-Arg0,Hyp3,Thi5,8,D-Phe7]bradykinin (pA2 = 9.6 +/- 0.4) were greater than those with des-Arg9-[Leu8]bradykinin (pA.2 = 7.8 +/- 0.3). These results suggest that two apparently distinct types of BK receptors may exist in basilar arteries. Furthermore, the contractile response to bradykinin in basilar artery was significantly inhibited by 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (10(-5) M), H-7 (10(-5) M) and TMB-8 (10(-5) M), but not by indomethacin (10(-5) M) or nordihydroquariaretic acid (10(-5) M). On the other hand, nifedipine, Ca(2+)-free medium, EGTA and Ca(2+)-free medium/EGTA significantly reduced the bradykinin-induced contraction, indicating that part of the contractile response of basilar artery to bradykinin is dependent on extracellular Ca2+. In conclusion, the mechanism of the contractile responses to bradykinin in basilar artery may involve increased intracellular Ca2+ levels acting on the BK1 and BK2 receptor, followed by activation of the phosphoinositide pathway and receptor-mediated Ca2+ channel.

Animals↗
PubMed1996

Integrin alpha v beta 3 and phospholipase C regulate prostacyclin formation of endothelial cells caused by ancrod-generated fibrin.

Ancrod-generated fibrin has been shown to stimulate prostacyclin synthesis of human umbilical vein endothelial cells (Chang et al., 1994, Biochem. Biophys. Res. Commun. 203, 1920). We further investigated its mechanism of action. The increment of 6-keto prostaglandin F1 alpha stimulated by ancrod-generated fibrin was almost completely inhibited when endothelial cells were either pretreated with 50 microM 8-(N,N'-diethylamino)octyl-3,4,5- trimethoxybenzoate (TMB-8) or preloaded with 15 microM 1,2-bis(2- aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). 6-Keto prostaglandin F1 alpha production during 2 and 10 h incubation period was also inhibited by 1.2 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraace tic acid (EGTA) (41 +/- 12 and 53 +/- 17% inhibition, respectively). Further, ancrod-generated fibrin caused a rapid-onset increase in [3h]inositol monophosphate (IP1) formation in endothelial cells. This increase in IP1 was significantly inhibited by 1 mM Gly-Pro-Arg-Pro, 1 mM neomycin or 100 ng/ml pertussis toxin. At the same time, neomycin and pertussis toxin also significantly inhibited 6-keto prostaglandin F1 alpha synthesis of endothelial cells stimulated by ancrod-generated fibrin. Additionally, the increment of IP1 production as well as prostacyclin production were significantly inhibited by monoclonal antibodies directed against alpha v beta 3. These results suggest that intra- and extra-cellular Ca2+ participate in prostacyclin synthesis stimulated by ancrod-generated fibrin. Ancrod-generated fibrin stimulates pertussis toxin-sensitive G-protein regulated phosphoinositide breakdown, which is responsible for prostacyclin synthesis. This augmentation in prostacyclin synthesis and phosphoinositide breakdown caused by ancrod-generated fibrin area, at least in part, mediated by fibrin binding to integrin alpha v beta 3 on endothelial cells.

6-Ketoprostaglandin F1 alpha↗
PubMed1987

The role of cAMP and calcium in the stimulation of proliferation of immature erythroblasts by erythropoietin.

The hypothesis that cAMP or calcium are the second messengers of erythropoietin (Epo) was tested on fractionated, Epo-responsive immature erythroblasts from anemic rabbit bone marrow by examining whether the proliferative effects of the hormone could be mimicked by agents that increase the intracellular concentration of cAMP or Ca2+. None of the compounds tested (including 10(-6)-10(-4) M db-cAMP, forskolin, isoprenaline or 10(-7)-10(-6) M of the calcium ionophore A23187) alone or in combination could either initiate or potentiate the mitogenic action of the hormone. Furthermore, addition of 0.2 U/ml erythropoietin produced no permanent or transient increase in the uptake of 45Ca2+ by erythroblasts at 37 degrees C. However, cells cultured with imidazole or cordycepin (which reduce the level of intracellular cAMP), or with the calcium chelator EGTA, or the drugs verapamil or TMB-8 (which interfere with the utilization of extracellular or intracellular calcium) showed a decreased stimulation of DNA synthesis by Epo. Finally, the tumour promoter phorbol ester TPA could partially mimic the action of Epo when added to cultures containing more immature progenitor cells. We conclude then that an artificial increase in the cytoplasmic concentration of either cAMP or Ca2+ is not sufficient to elicit the proliferation of Epo-responsive cells.

Animals↗
PubMed1986

Origin and distribution of phrenic primary afferent nerve fibers in the spinal cord of the adult rat.

Previous studies from this laboratory have localized and morphologically characterized phrenic motor neurons in the rat spinal cord at light and electron microscopic levels. The present investigation used a modification of the TMB method for the retrograde transport of horseradish peroxidase (HRP) to describe at light microscope levels the origin and distribution of phrenic primary afferent axons in the adult rat spinal cord. Dry HRP crystals were applied to the central stump of the transected phrenic nerve in the neck to label spinal ganglion cell bodies and thus determine the levels of origin of afferent axons in the phrenic nerve. Camera lucida drawings were then made from serial sections through the appropriate spinal cord levels to determine the specific distribution of transganglionically labeled phrenic central axonal processes within the spinal cord. HRP-labeled phrenic primary neurons were observed in the C3 to C7 spinal ganglia. The camera lucida studies indicated that the transganglionically labeled central processes of phrenic primary afferent axons distributed into the dorsal horn at the C4 and C5 levels of the spinal cord. Furthermore, central processes distributing to C5 were more numerous than those that distributed to C4. Afferent axons were never seen in the dorsal horn at C3, C6, or C7. As spinal ganglion cells were labeled at C3 above and C6 and C7 below, it follows that central processes of phrenic afferent fibers descend and ascend in the dorsal columns of the spinal cord before distributing into the dorsal horn. Specifically, the labeled primary afferent axons and their collateral branches were found in the fasciculus cuneatus, and in laminae I, II, III, and IV of the dorsomedial aspect of the dorsal horn. The function of these central axonal processes is unknown, but based on a comparison of our morphologic data with previous physiological and anatomical studies, we suggest that phrenic afferent fibers may arise from proprioceptors (muscle spindles and Golgi tendon organs), nociceptors, or rapidly adapting mechanoreceptors (Pacinian corpuscles) within the diaphragm.

Afferent Pathways↗
PubMed1988

Fetal frontal cortex transplanted to injured motor/sensory cortex of adult rats: reciprocal connections with host thalamus demonstrated with WGA-HRP.

Fetal frontal cortex was transplanted into lesion cavities formed in host motor/sensory cortex of adult rats. Eight to twenty-eight weeks later wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was injected into host thalamus and the brain was sectioned and reacted using a sensitive TMB procedure. A large amount of fine granular WGA-HRP was detected in most transplants. This could represent anterograde transport demonstrating that injured adult host thalamic neurons sprouted axons into fetal cortical transplants. Conversely, none or very few retrogradely labeled pyramidal neurons were present in the transplants. This indicates that pyramidal neurons in transplants either did not sprout into adult host brain or sprouted such short distances that they did not pick up the WGA-HRP. These results are compatible with the hypothesis that high trophic/growth factor levels in newborn or fetal brain and low levels in adults determine the more extensive connections seen in newborn hosts compared with those in adult transplanted hosts. The data are also consistent with the proposal that adult host brains impair axonal growth. Functionally, the data suggest that although corticofugal effects of fetal cortical transplants in adult host brains are likely to be limited, transplants could exert beneficial trophic effects on adult host thalamic neurons.

Animals↗
PubMed1991

Schistosoma mansoni: possible involvement of protein kinase C in linoleic acid-induced proteolytic enzyme release from cercariae.

The possible involvement of protein kinase C and Ca2+ metabolism in the proteolytic enzyme release from schistosome cercariae was studied. Cercariae were placed in dechlorinated tap water containing 0.37 mM calcium in the small glass petri dish and exposed to the stimuli (linoleic acid, phorbol esters, and Ca2+ ionophore) with or without inhibitors of protein kinase C or Ca2+ metabolism. The proteolytic activity of incubation medium of cercariae thus treated was measured by the azocoll assay. The penetration response of cercariae induced by linoleic acid, a physiological stimulus, was mimicked by phorbol esters. When exposed to phorbol esters, 0.02 to 2 microM of 12-O-tetradecanoylphorbol-13-acetate (TPA) and 0.2 to 2 microM of phorbol-12,13-dibutyrate (PDBu), cercariae ceased the swimming movement, began a rhythmic thrusting of the anterior tip of the parasite, and released the proteolytic enzyme, but they did not shed the tails. Lowering Ca2+ in water by addition of 5 mM ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), phorbol ester-induced release of enzyme was completely inhibited. Phorbol ester-induced release of enzyme was partially inhibited by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C, at a concentration of 100 microM. H-7 alone, at a concentration of 100 microM, did not affect the swimming movement of cercariae. The cercariae were stimulated to release the enzyme by high concentrations (10 and 100 microM) of the Ca2+ ionophore, A23187, but enzyme was not released by low concentrations (0.5 and 1 microM) of this drug. Cercariae exposed to A23187 behaved differently from those exposed to phorbol esters. They ceased swimming, showed strong muscle contraction, and shed their tail. A23187 stimulated cercariae to release the enzyme in the water containing 5 mM EGTA. A23187-induced enzyme release was not inhibited by N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a calmodulin antagonist, trifluoperazine (TFP), a better calmodulin antagonist on schistosome, or by verapamil, a Ca2+ channel blocker. Linoleic acid-induced release of enzyme was partially inhibited by 0.5 and 5 mM of EGTA and by 1 to 100 microM of H-7. While it was not inhibited by N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H-8) and N-(2-guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004), inhibitors of cyclic nucleotide-dependent protein kinase which were used as negative controls of H-7, W-7, TFP, 8-(N,N-diethylamino)octyl 3,4,5-trimethoxybenzoate (TMB-8), an intracellular Ca2+ antagonist, and verapamil.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

The platelet activation induced by wheat germ agglutinin.

In human platelets, wheat germ agglutinin (WGA) induced serotonin release without cell agglutination. WGA induced the phosphorylation of both 40-kDa and 20-kDa proteins in a parallel manner, and at least, the phosphorylation of 40-kDa protein was preceded by transient formation of endogenous diacylglycerol (DG) accompanied by a decrease in phosphatidylinositol (PI). Both phosphorylation of these two proteins and serotonin release were inhibited by prior treatment of platelets with dibutyryl cyclic AMP, W-7, or TMB-8. These results suggest that both phosphatidylinositol turnover and Ca2+ mobilization play an essential role in WGA-induced platelet activation.

Aminoquinolines↗
PubMed1986

Intracellular Ca2+-calmodulin system involved in the palytoxin-induced K+ release from rabbit erythrocytes.

Palytoxin (PTX) caused K+ release from rabbit erythrocytes which was dependent on the concentrations of extracellular Ca2+ and PTX. In a Ca2+-free solution, PTX still caused a slow K+ release. An intracellular Ca2+ antagonist, TMB-8, an intracellular Ca2+ chelator, quin 2, and calmodulin inhibitors, prenylamine, W-7 and W-5, inhibited the PTX-induced K+ release in a Ca2+-free solution. These results suggest that the PTX-induced K+ release is dependent on the process including intracellular Ca2+ and calmodulin.

Acrylamides↗
PubMed1987

Calcium ionophore A23187 enhances human neutrophil superoxide release, stimulated by phorbol dibutyrate, by converting phorbol ester receptors from a low- to high-affinity state.

The calcium ionophore A23187 acted synergistically with phorbol dibutyrate (PDBu) to stimulate human neutrophil superoxide production. A23187 shortened the lag period and markedly increased the initial rate of neutrophil superoxide production induced by suboptimal concentrations of PDBu. 1 microM A23187 reduced the EC50 value for superoxide release from 56 to 8 nM PDBu. This effect of A23187 was correlated with enhanced binding of [3H]PDBu to its receptor and a reduction in the dissociation constant (Kd) from 27 to 10 nM, without altering the apparent total number of phorbol dibutyrate receptors. These actions of A23187 were abolished in the presence of EGTA or TMB-8, confirming a dependence on Ca2+.

Caenorhabditis elegans Proteins↗
PubMed1990

Ins(1,4,5)P3 formation and fluctuating chloride current response induced by external ATP in Xenopus oocytes injected with embryonic guinea pig brain mRNA.

In voltage-clamped Xenopus oocytes injected with embryonic guinea pig mRNA, effective concentrations of extracellular ATP elicited an inward fluctuating current. This current, carried by Cl-ions, was mainly dependent upon liberation of Ca2+ ions from stores as demonstrated by experiments using intracellular EGTA loading and TMB-8 superfusion. Neomycin inhibited these fluctuating currents indicating that the transplanted purinoceptor is linked to phospholipase C activity and triggers Ins(1,4,5)P3 formation. Ins(1,4,5)P3 production evoked by external ATP was clearly demonstrated by directly measuring the water-soluble Ins(1,4,5)P3 level in injected oocytes. Finally, it is suggested that the ATP effect was mediated by a Ca2+ release from Ins(1,4,5)P3 sensitive pools since heparin blocked the ATP responsiveness. The acquired purinoceptor may be made apparent to a P2 subtype since ATP and ADP were equipotent in eliciting Cl- current while AMP and Adenosine were ineffective in injected oocytes.

Adenosine↗
PubMed1990

Functional involvement of calcium in the homologous up-regulation of the 1,25-dihydroxyvitamin D3 receptor in osteoblast-like cells.

In several cell types 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) causes up-regulation of its receptor. The present study demonstrates that in the osteoblast-like cell line UMR 106 this up-regulation is inhibited by two different calcium channel blockers (nitrendipine, verapamil). Also with chelating extracellular calcium (EGTA) and by inhibition of calcium release from intracellular stores (TMB-8) comparable results were obtained. These findings indicate that calcium is functionally involved in this cellular response to the steroid hormone 1,25(OH)2D3. Moreover, data obtained with EGTA show that the 1,25(OH)2D3 receptor level is closely regulated by the extracellular calcium concentration.

Calcitriol↗