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S Dissing

Publications and source records attributed to S Dissing.

At least 37 records · Page 2Linked to original sources
PubMed1996

ATP activates K and Cl channels via purinoceptor-mediated release of Ca2+ in human coronary artery smooth muscle.

Coronary artery smooth muscle cells express G protein-coupled purinoceptors, and we report here for the first time how receptor activation by extracellular ATP influences cell membrane currents and membrane potential in human cells. ATP (100 microM) stimulated a triphasic change in membrane potential lasting several seconds, which was caused by sequential opening of transient inward and outward conductances. The inward current was carried by Cl- and the outward current by K+, as shown by ion substitution and changes in holding potential. Both currents were independent of the presence of external Ca2+ but were blocked by strong buffering of Ca2+ in the internal solution. The P2u- and P2y-purinoceptor agonists UTP and 2-methylthioadenosine 5'-triphosphate activated similar currents, whereas the P2x-receptor agonist alpha, beta-methyleneadenosine 5'-triphosphate and the P1-receptor agonist adenosine failed to stimulate any whole cell currents. The ATP-activated K+ current was inhibited by iberiotoxin (200 nM), and it was potentiated by the BK channel activator NS-1619 (30 microM). In cell-attached recordings, ATP activated a 230-pS BK channel. In conclusion, ATP acting via P2 purinoceptors stimulated release of Ca2+ from internal stores and transiently activated depolarizing Cl- and hyperpolarizing BK channels in human coronary artery smooth muscle cells.

Adenosine Triphosphate↗
PubMed1995

Activation of P2z purinoceptors diminishes the muscarinic cholinergic-induced release of inositol 1,4,5-trisphosphate and stored calcium in rat parotid acini. ATP as a co-transmitter in the stimulus-secretion coupling.

The effect of extracellular ATP on the intracellular free Ca2+ concentration ([Ca2+]i) and inositol phosphate production following stimulation with the muscarinic cholinergic agonist acetylcholine (ACh) was investigated in isolated rat parotid acinar cells. Stimulation of rat parotid acinar cells with ATP4- results in a rise in [Ca2+]i that is due to influx of extracellular Ca2+ and mobilization of Ca2+ from intracellular stores. Stimulation with purinergic agonists revealed that both influx as well as Ca2+ release from intracellular stores was mediated through activation of P2z receptors. The Ca2+ mobilization from intracellular stores was due to production of Ins(1,4,5)P3 and was inhibited by U73122, an inhibitor of phospholipase C-coupled processes. Under Ca(2+)-free conditions ATP4- caused a dose-dependent inhibition (IC50 = 8 microM) of the ACh-evoked Ca2+ release. The inhibitory effect of ATP4- is due to activation of the P2z purinoceptors, which results in a strong reduction in the ACh-induced inositol phosphate production. Prestimulation with 100 microM ATP4- reduced the amount of Ins(1,4,5)P3 formed after maximal ACh stimulation by 91%. In conclusion, the inhibitory effect of ATP4- on the ACh-mediated response is due to interactions of the activated P2z receptor with the phospholipase C-coupled processes underlying the muscarinic cholinergic response.

Acetylcholine↗
PubMed1995

Stimulation of cloned human glucagon-like peptide 1 receptor expressed in HEK 293 cells induces cAMP-dependent activation of calcium-induced calcium release.

The actions of glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) on cellular signalling were studied in human embryonal kidney 293 (HEK 293) cells stably transfected with the cloned human GLP-1 receptor. The cloned GLP-1 receptor showed a single high-affinity binding site (Kd = 0.76 nM). Binding of GLP-1(7-36)amide stimulated cAMP production in a dose-dependent manner (EC50 = 0.015 nM) and caused an increase in the intracellular free Ca2+ concentration ([Ca2+]i). The latter effect reflected Ca(2+)-induced Ca2+ release and was suppressed by ryanodine. We propose that the ability of GLP-1(7-36)amide to increase [Ca2+]i results from sensitization of the ryanodine receptors by a protein kinase A dependent mechanism.

Acetylcholine↗
PubMed1995

Cyclic ADP-ribose and inositol 1,4,5-triphosphate mobilizes Ca2+ from distinct intracellular pools in permeabilized lacrimal acinar cells.

In permeabilized lacrimal acinar cells, cyclic ADP-ribose (cADP-ribose) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) release Ca2+ in a dose dependent manner from distinct thapsigargin-sensitive Ca2+ pools. Ryanodine specifically blocks the Ca2+ response to cADP-ribose, whereas heparin strongly reduces the response to Ins(1,4,5)P3 application. GTP causes a rapid Ca2+ release by a ryanodine- and heparin-insensitive mechanism and potentiates Ins(1,4,5)P3 but not cADP-ribose evoked Ca2+ release. It is estimated that cADP-ribose can release 16 mumol Ca2+/l cells, whereas Ins(1,4,5)P3 can mobilize 55 mumol Ca2+/l cells. The results suggest that cADP-ribose and Ins(1,4,5)P3 release Ca2+ from distinct internal stores and that a third Ca2+ pool exists which can selectively interact with the Ins(1,4,5)P3-sensitive Ca2+ store by a GTP-mediated process.

Adenosine Diphosphate Ribose↗
PubMed1995

The release of intracellular Ca2+ in lacrimal acinar cells by alpha-, beta-adrenergic and muscarinic cholinergic stimulation: the roles of inositol triphosphate and cyclic ADP-ribose.

Stimulation of rat lacrimal acinar cells with acetylcholine (ACh) and the beta-adrenergic agonist isoprenaline causes a rapid increase in inositol phosphates with 1-4 phosphate groups, resulting in release of Ca2+ from intracellular stores. Stimulation with the alpha-adrenergic agonist phenylephrine, however, causes a release of Ca2+ from internal stores which is 36% of that observed with ACh stimulation, but without inositol phosphate production. This Ca2+ rise was completely inhibited by 100 microM ryanodine. Adrenaline (causing activation of both alpha- and beta-adrenergic receptors) induces a Ca2+ release with inositol phosphate synthesis identical to that occurring in the beta-adrenergic response. Thus, the signalling pathway for alpha-adrenergic stimulation occurs via a path different from that which releases Ca2+ via muscarinic cholinergic and beta-adrenergic stimulation. In permeabilized lacrimal acinar cells cyclic adenosine 5'-diphosphoribose (cADP-ribose) and inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] cause release of Ca2+ from intracellular stores. The Ca2+ release evoked by cADP-ribose, but not by Ins(1,4,5)P3, was abolished by 100 microM ryanodine, implicating a possible involvement of cADP-ribose in phenylephrine-induced Ca2+ signalling. When the intracellular free Ca2+ concentration ([Ca2+]i) is raised by application of ionomycin, inositol phosphates are synthesized with a half-maximal effect seen at 425 nM. In contrast, loading cells with the Ca2+ chelator 1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) reduced the adrenaline-induced inositol phosphate synthesis by 27%. The stimulation-induced rise in [Ca2+]i, therefore, appears to cause further synthesis of inositol phosphates, thereby amplifying the receptor-mediated response.

Acetylcholine↗
PubMed1995

Effects of the hypoglycaemic drugs repaglinide and glibenclamide on ATP-sensitive potassium-channels and cytosolic calcium levels in beta TC3 cells and rat pancreatic beta cells.

The present study demonstrates the action of the hypoglycaemic drugs repaglinide and glibenclamide in cultured newborn rat islet cells and mouse beta TC3 cells. In cell-attached membrane patches of newborn rat islet cells repaglinide (10 nmol/l) and glibenclamide (20 nmol/l) decrease the open probability of single ATP-sensitive K(+)-channels to approximately 10% of the activity prior to addition of the drugs in short-term experiments (< 5 min). The influence of repaglinide and glibenclamide on the ATP-sensitive K+ current was studied using the whole-cell patch clamp configuration. A half-maximal steady-state inhibition of the ATP-sensitive K+ currents is observed at 89 pmol/l repaglinide and at 47 pmol/l glibenclamide in whole-cell experiments of longer duration (30 min). Applying digital Ca2+ imaging on single beta TC3 cells we found that repaglinide and glibenclamide induced a concentration-dependent increase in intracellular free Ca2+ concentration ([Ca2+]i) with a half-maximal effect at 0.5 nmol/l for both drugs in long-term experiments (30 min). The rise in [Ca2+]i results from Ca2+ entry through voltage-dependent L-type Ca(2+)-channels since it is inhibited by verapamil (10 mumol/l). The effect of repaglinide and glibenclamide is partly reversible (approximately 80%).

Adenosine Triphosphate↗
PubMed1995

Role of protein kinase C in the regulation of inositol phosphate production and Ca2+ mobilization evoked by ATP and acetylcholine in rat lacrimal acini.

Stimulation of rat lacrimal acinar cells with ATP and acetylcholine (ACh) induced a rapid accumulation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] and its degradation products, resulting in an initial release of Ca2+ from intracellular stores. However, after pretreating the acini with U73122 no increase in the intracellular free Ca2+ concentration ([Ca2+]i) or Ins(1,4,5)P3 production was observed. A short pretreatment with the phorbol ester 4-beta-phorbol-12-beta-myristate-13-alpha-acetate (PMA) significantly attenuated the ATP- and ACh-induced increase in [Ca2+]i and overall inositol phosphate production. In contrast, staurosporine enhanced Ins(1,4,5)P3 and inositol 1,3,4-trisphosphate [Ins(1,3,4)P3] production and [Ca2+]i above control values in ATP- and ACh-stimulated cells. Stimulation of phospholipase C by ionomycin-evoked changes in [Ca2+]i were unaltered by pretreatment with staurosporine and PMA. The data show that a change in protein kinase C activity during cell stimulation affects the inositol phosphate metabolism and thereby the cellular Ca2+ signalling processes in lacrimal acinar cells.

Acetylcholine↗
PubMed1995

Glucagon-like peptide I increases cytoplasmic calcium in insulin-secreting beta TC3-cells by enhancement of intracellular calcium mobilization.

In the insulin-secreting beta-cell line beta TC3, stimulation with 11.2 mmol/l glucose caused a rise in the intracellular free Ca2+ concentration ([Ca2+]i) in only 18% of the tested cells. The number of glucose-responsive cells increased after pretreatment of the cells with glucagon-like peptide I (GLP-I)(7-36)amide and at 10(-11) mol/l; 84% of the cells responded to glucose with a rise in [Ca2+]i. GLP-I(7-36)amide induces a rapid increase in [Ca2+]i only in cells exposed to elevated glucose concentrations (> or = 5.6 mmol/l). The action of GLP-I(7-36)amide and forskolin involved a 10-fold increase in cytoplasmic cAMP concentration and was mediated by activation of protein kinase A. It was not associated with an effect on the membrane potential but required some (small) initial entry of Ca2+ through voltage-dependent L-type Ca2+ channels, which then produced a further increase in [Ca2+]i by mobilization from intracellular stores. The latter effect reflected Ca(2+)-induced Ca2+ release and was blocked by ryanodine. Similar increases in [Ca2+]i were also observed in voltage-clamped cells, although there was neither activation of a background (Ca(2+)-permeable) inward current nor enhancement of the voltage-dependent L-type Ca2+ current. These observations are consistent with GLP-I(7-36) amide inducing glucose sensitivity by promoting mobilization of Ca2+ from intracellular stores. We propose that this novel action of GLP-I(7-36)amide represents an important factor contributing to its insulinotropic action.

Animals↗
PubMed1993

Ca2+ signalling in exocrine acinar cells: the diffusional properties of cellular inositol 1,4,5-trisphosphate and its role in the release of Ca2+.

The correlation between acetylcholine induced changes in the intracellular free, Ca2+ concentration ([Ca2+]i), and the inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) content in isolated acini from the rat parotid and lacrimal glands was investigated. Applying digital image processing on Fura-2 loaded acini, we observed that Ca2+ increases either simultaneously throughout the acinar configurations or that occasionally, the rise near the lumen can precede the rise near the basal part by 50-100 ms. Measurements on cell suspensions revealed a correlation between changes in [Ca2+]i and changes in the cellular Ins(1,4,5)P3 content, and it is concluded that in the individual cells Ins(1,4,5)P3 is released to the cytosol within the first second after stimulation. Applying a diffusion coefficient for cytoplasmic Ins(1,4,5)P3 of 2.83 x 10(-6) cm2/s (Allbritton et al., 1992, Science, 258, 1812-1815), we have calculated the concentration profile for this messenger in a sphere with a radius of 10 microns where Ins(1,4,5)P3 is released in the center following a monoexponential function with a rate constant of 4 s-1. Assuming that Ins(1,4,5)P3 concentrations of 1 or 5% of the maximum value is able to release Ca2+, we calculated that Ca2+ waves can appear at a rate of 100 or 40 microns/s. The present data are consistent with Ins(1,4,5)P3 being a cellular messenger, that by diffusion, initiates the Ca2+ release from the cellular pools within the first fraction of a second.

Acetylcholine↗
PubMed1993

T-cell activation. V. Anti-major histocompatibility complex class I antibody-induced activation and clonal abortion in Jurkat T-leukaemic cells.

We have studied activation-induced changes in intracellular calcium [Ca2+]i, interleukin-2 (IL-2) secretion, and clonal abortion of the human leukaemic T-cell line Jurkat and three T-cell receptor (TcR)/CD3 receptor negative clones deficient for the TcR alpha, TcR beta and CD3 gamma chains respectively, as well as three transfectant clones reconstituted with the appropriate TcR/CD3 cDNA. For activation, the cells were exposed to anti-TcR/CD3, anti-CD2 and anti-major histocompatibility complex (anti-MHC) class I monoclonal antibodies (mAb) respectively. Cellular activation by these mAb leading to an increased IL-2 secretion was preceded by a rise in [Ca2+]i and was relatively dependent on the expression of the a TcR/CD3 complex. In contrast, anti-MHC class I mAb-induced clonal abortion in Jurkat T cells may occur without previous fluctuations in [Ca2+]i and appeared to be independent of TcR/CD3 expression. The present observation suggest the existence of different secondary messenger systems operating in Jurkat cells following activation via the TcR/CD3, CD2 and the MHC class I pathways, respectively.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1990

Inhibitory effects of amitriptyline on the stimulation-induced Ca2+ increase in parotid acini.

The present study demonstrates the effects of the antidepressant, amitriptyline, and the acetylcholine antagonist, atropine, on the stimulation-induced rise in cytosolic, free Ca2+ (Cai2+). The changes in Cai2+ of collagenase-isolated rat parotid acini were measured by means of the Ca2(+)-sensitive dye, fura-2. It was found that stimulation by carbachol resulted in a maximal increase of 582 +/- 34 nM (mean +/- S.E.) in Cai2+ with a ks of 5.8 +/- 1.3 microM. Adrenaline caused a rise of 380 +/- 22 nM in Cai2+ with a ks of 0.5 +/- 0.2 microM. Amitriptyline and atropine were found to inhibit the carbachol-induced rise in Cai2+ with dissociation constants (kI) of 105 and 1.25 nM, respectively, in the absence of agonist. The adrenergic-induced rise in Cai2+ was inhibited by amitriptyline with a kI of 45 nM. Amitriptyline was found to inhibit both receptor classes by a competitive or mixed type of inhibition. Similarly, atropine exerted the same type of inhibition on the acetylcholine receptor. Amitriptyline and atropine were found to be mutually exclusive for competing for substrate binding on the receptor. These findings are consistent with a common binding site for amitriptyline and atropine on the acetylcholine receptor, possibly in close proximity with, but different from the substrate binding site. The stimulation-induced cell shrinkage evoked by the loss of electrolytes and water from the acini was measured by a 90 degree light scattering signal. It was found that this method makes possible the detection of autonomic side-effects of antidepressants on acini suspended in protein-containing media.

Amitriptyline↗
PubMed1990

Spatial distribution of intracellular, free Ca2+ in isolated rat parotid acini.

The spatial distribution of intracellular, free Ca2+ ([Ca2+]i) in rat parotid acini was measured by imaging fura-2 fluorescence from individual acinar cells by means of a digital imaging microscope. Upon cholinergic stimulation in a Krebs-Ringer bicarbonate buffer at (37 degrees C), [Ca2+]i increased synchronously at both the basolateral and luminal membranes as well as in all cells of the secretory endpiece, reaching peak [Ca2+]i levels 1 s after stimulation. Atropine addition caused a rapid down-regulation of [Ca2+]i, which, however, never reached prestimulatory levels. When acini were stimulated in a medium containing 5 nM Ca2+, the Ca2+ mobilization arising from internal pools caused an increase in [Ca2+]i predominantly near the basolateral area, where the endoplasmic reticulum is located, and standing Ca2+ gradients were observed for up to 10 s. A mathematical model is developed to simulate the time courses of the Ca2+ profiles through the cytoplasm using estimated values of the Ca2+ diffusion coefficients and the cytosolic Ca2+ buffering capacity. It is concluded that under physiological conditions, the Ca2+ release from the endoplasmic reticulum is responsible for the activation of the basolaterally located K+ channels. Furthermore, Ca2+ influx from the interstitium is responsible for much of the rise in [Ca2+]i near the luminal membranes, where the Cl- channels are supposed to be located.

Animals↗
PubMed1990

T cell activation. II. Activation of human T lymphoma cells by cross-linking of their MHC class I antigens.

The present work demonstrates that antibody-induced cross-linking of MHC class I antigens on Jurkat T lymphoma cells leads to a rise in intracellular calcium (Cai2+) and, in the presence of phorbol ester (PMA), to IL-2 production and IL-2 receptor expression. The rise in Cai2+ exhibited a profile very different from that obtained after anti-CD3 antibody-induced activation suggesting that activation signals are transduced differently after binding of anti-CD3 antibody and class I cross-linking, respectively. However, when Cai2+ was examined in individual Jurkat cells by means of a digital image processing system no differences were observed after cross-linking with anti-CD3 and anti-MHC class I antibodies, respectively. Two CD3-negative mutant lymphoma lines were nearly totally refractory to class I cross-linking. Taken together our results may indicate the existence of a functional linkage between the T cell receptor complex and MHC class I molecules.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1990

Anion-coupled Na efflux mediated by the human red blood cell Na/K pump.

The red cell Na/K pump is known to continue to extrude Na when both Na and K are removed from the external medium. Because this ouabain-sensitive flux occurs in the absence of an exchangeable cation, it is referred to as uncoupled Na efflux. This flux is also known to be inhibited by 5 mM Nao but to a lesser extent than that inhibitable by ouabain. Uncoupled Na efflux via the Na/K pump therefore can be divided into a Nao-sensitive and Nao-insensitive component. We used DIDS-treated, SO4-equilibrated human red blood cells suspended in HEPES-buffered (pHo 7.4) MgSO4 or (Tris)2SO4, in which we measured 22Na efflux, 35SO4 efflux, and changes in the membrane potential with the fluorescent dye, diS-C3 (5). A principal finding is that uncoupled Na efflux occurs electroneurally, in contrast to the pump's normal electrogenic operation when exchanging Nai for Ko. This electroneutral uncoupled efflux of Na was found to be balanced by an efflux of cellular anions. (We were unable to detect any ouabain-sensitive uptake of protons, measured in an unbuffered medium at pH 7.4 with a Radiometer pH-STAT.) The Nao-sensitive efflux of Nai was found to be 1.95 +/- 0.10 times the Nao-sensitive efflux of (SO4)i, indicating that the stoichiometry of this cotransport is two Na+ per SO4=, accounting for 60-80% of the electroneutral Na efflux. The remainder portion, that is, the ouabain-sensitive Nao-insensitive component, has been identified as PO4-coupled Na transport and is the subject of a separate paper. That uncoupled Na efflux occurs as a cotransport with anions is supported by the result, obtained with resealed ghosts, that when internal and external SO4 was substituted by the impermeant anion, tartrate i,o, the efflux of Na was inhibited 60-80%. This inhibition could be relieved by the inclusion, before DIDS treatment, of 5 mM Cli,o. Addition of 10 mM Ko to tartrate i,o ghosts, with or without Cli,o, resulted in full activation of Na/K exchange and the pump's electrogenicity. Although it can be concluded that Na efflux in the uncoupled mode occurs by means of a cotransport with cellular anions, the molecular basis for this change in the internal charge structure of the pump and its change in ion selectivity is at present unknown.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

T-cell activation. III. Attempts to activate MHC class I-negative and class I-transfected EL4 T-lymphoma cells by immobilized anti-CD3 antibody.

The aim of this study was to examine whether the unresponsiveness of MHC class I-negative subclones of the EL4 thymoma to CD3 cross-linking can be restored by transfection of class I genes into the H-2-negative cells. Cell activation experiments with selected MHC class I-negative subclones and H-2b- and H-2Ld-positive transfectants showed that these cells are equally capable of secreting interleukin 2 (IL-2) after exposure to the phorbol ester phorbol 12-myristate 13-acetate (PMA) and ionomycin. In contrast, only the parental H-2-positive EL4 cells are capable of responding to treatment with immobilized anti-CD3 antibody with IL-2 secretion and IL-2 receptor expression. Measurements of intracellular free Ca2+ (Ca2+i) following anti-CD3 antibody-induced cross-linking of parental EL4 cells and H-2-negative and H-2b gene-transfected subclones showed that the parental cells and two of the class I transfectants, one H-2-positive and one H-2-negative, responded with a slow rise in Ca2+i, whereas one H-2-positive transfected cell clone was completely refractory to CD3 cross-linking. Modulation experiments using parental EL4 cells, H-2-negative subclones and H-2-positive transfectants demonstrated that the CD3 and class I molecules of these different cells are modulated to the same extent after exposure to specific antibodies. The present findings thus indicate that the unresponsiveness of H-2-negative EL4 subclone cells to CD3 cross-linking is not functionally associated with a lack of class I surface expression.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1990

Na+ transport properties of isolated rat parotid acini.

The effect of carbachol stimulation on the Na+ transport properties of rat parotid acini was characterized. Upon stimulation, the acinar Na+ concentration increased from 20 to 70 mM within 25 s, whereafter a backregulation toward the prestimulatory level was observed, mediated by the Na(+)-K+ pump. The transport mechanisms responsible for the net Na+ uptake observed between 10 and 20 s after carbachol stimulation in a Krebs-Ringer-bicarbonate medium (KRB) consisted of a dimethylamiloride-sensitive Na(+)-H+ exchange system (3.5 mmol.liter cell water-1.s-1 or approximately 75% of the total Na+ influx) and a bumetanide-sensitive cotransport system (of approximately 15%). The data are consistent with the residual influx being mediated by amiloride-sensitive Na+ channels. In unstimulated acini acidified by a NH4+ prepulse technique, the relationship between intracellular pH (pHi) and the rate of acinar Na(+)-H+ exchange was determined. At pHi 6.5 the rate of Na(+)-H+ exchange in a KRB medium amounted to 1.2 mmol.liter cell water-1.s-1 and ceased when pHi had recovered to 7.2. It was concluded that under physiological conditions carbachol stimulation activates Na(+)-H+ exchange, an effect that is responsible for the major part of the Na+ gain after stimulation. The role of cotransport in mediating net Cl- uptake against an electrochemical gradient was investigated. It was found that when the Na+ gradient is strongly reduced (in a 20 mM Na+ medium) a Cl(-)-HCO3- exchange system can mediate a net Cl- uptake at a rate similar to the rate observed in a medium containing high Na+. The results are compatible with both Cl(-)-HCO3- exchange and cotransport keeping an intracellular Cl- concentration above the electrochemical equilibrium under physiological conditions.

Acetazolamide↗
PubMed1989

Anticholinergic effects of cis-chlorprothixene characterized in rat parotid acini.

The anticholinergic effects of the antipsychotic drug, cis-chlorprothixene, on the secretory events underlying the formation of primary saliva were investigated. The neuroleptic, cis-chlorprothixene, is used extensively as a major tranquillizer but shares side-effects such as xerostomia with most antidepressants. The inhibitory effects of cis-chlorprothixene upon the cholinergic-induced rise in Ca2+ as well as on O2 consumption and Cl- loss were investigated in isolated rat parotid acini in order to characterize its anticholinergic effects quantitatively. The cholinergic-induced rise in cytosolic, free Ca2+ was inhibited by cis-chlorprothixene with half-maximal effect at 1.9 microM and maximal inhibition at 10 microM. When the cytosolic, free Ca2+ was enhanced in the presence of 10 microM cis-chlorprothixene by means of the Ca2+ ionophore A23187, a loss of Cl- was observed similar to that observed during cholinergic stimulation in the absence of cis-chlorprothixene. The findings are consistent with the possibility that cis-chlorprothixene exerts its effects on the steps leading from agonist binding to the acetylcholine receptor and to the increase of cytosolic free Ca2+. Thus, measurement of the stimulation-induced rise in cytosolic, free Ca2+ in the presence of neuroleptics such as the thioxanthenes represents a fast and reliable method for detecting inhibitory effects on autonomic receptor activation.

Animals↗