bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissociation of the effects of the antitumour ether lipid ET‐18‐OCH3 on cytosolic calcium and on apoptosis
Authors: Teresa Alonso Maria , Gajate Consuelo , Mollinedo Faustino , Modolell Manuel , Alvarez Javier , García‐Sancho Javier 
Published: August 2006

We have compared the effects of 1‐O‐octadecyl‐2‐O‐methyl‐sn‐glycero‐3‐phosphocholine (ET‐18‐OCH3) on the cytosolic free calcium concentration ([Ca2+]i) and on apoptosis in several normal and leukaemia cells, including human polymorphonuclear neutrophils (PMNs), U937 cells, and undifferentiated as well as dimethylsulphoxide‐differentiated HL60 cells (uHL60 and dHL60, respectively).
ET‐18‐OCH3 produced apoptosis, as evidenced by DNA degradation into oligonucleosome‐size fragments, in U937 and uHL60 cells, but not in dHL60 cells or PMNs.
ET‐18‐OCH3 induced an increase in [Ca2+]i mediated through the platelet‐activating factor (PAF) receptor in U937, dHL60 cells and PMNs, as shown by cross‐desensitization experiments and by prevention of the [Ca2+]i changes by the PAF antagonist WEB‐2170. The EC50 values for the increase in [Ca2+]i induced by PAF and ET‐18‐OCH3 were 5×10−11 and 2.5×10−7 M, respectively. In uHL60 cells the effect of ET‐18‐OCH3 on [Ca2+]i was very small and was not affected by WEB‐2170.
PAF did not produce apoptosis in any of the cell types tested. WEB‐2170 did not prevent the apoptosis induced by ET‐18‐OCH3.
The uptake of [3H]‐ET‐18‐OCH3 was much larger in U937 and uHL60 cells than in dHL60 cells and PMNs.
Our results indicate that the apoptotic effect of ET‐18‐OCH3 is not related to the changes in [Ca2+]i, effected by interaction with plasma membrane PAF receptors, but to other actions which are associated with the uptake of this drug into the cells.
Capsazepine block of voltage‐activated calcium channels in adult rat dorsal root ganglion neurones in culture
Authors: Docherty R J , Yeats J C , Piper A S 
Published: August 2006

We have found that capsazepine, a competitive antagonist at the vanilloid (capsaicin) receptor, blocks voltage‐activated calcium currents in sensory neurones.
The block of calcium current was slow to develop with a half time of about one minute at 100 μM and lasted for the duration of the experiment. The rate of block of calcium current was strongly concentration‐dependent.
The EC50 for the blocking effect at 0 mV was 7.7±1.4 μM after 6 min exposure to capsazepine. The EC50 at equilibrium was estimated to be 1.4±0.2 μM.
The block of calcium current showed some voltage‐dependence but there was no indication of any selectivity of action for a calcium channel subtype. The characteristics of the blocking action of capsazepine on the residual current of cells which were pretreated with either □Omega;‐conotoxin or nimodipine were similar to control.
The data suggest that capsazepine, in addition to its competitive antagonism of vanilloid receptors, has a non‐specific blocking action on voltage‐activated calcium channels which should be taken into account when interpreting the effects of this substance on intact preparations in vitro or in vivo.
Differential effects of zidovudine and zidovudine triphosphate on mitochondrial permeability transition and oxidative phosphorylation
Authors: Elimadi Aziz , Morin Didier , Albengres Edith , Chauvet‐Monges Anne‐Marie , Allain Valérie , Crevat Aimé , Tillement Jean‐Paul 
Published: August 2006

The effects of zidovudine (ZDV) and zidovudine triphosphate (ZDV‐3P) on Ca2+‐induced mitochondrial permeability transition (MPT), respiratory control ratio (RCR) and ATP synthesis have been investigated on isolated rat liver mitochondria.
ZDV slightly but significantly decreased RCR and ATP synthesis but was ineffective in inhibiting MPT. In contrast, ZDV‐3P did not alter RCR and ATP synthesis but strongly inhibited MPT (IC50=3.0±0.9 μM).
The effect of ZDV‐3P on mitochondrial swelling required a preincubation time. When incubated 10 min with mitochondria, ZDV‐3P (8 μM) totally inhibited the rate of swelling.
ADP, ATP and atractyloside, which are agents known to interact with the mitochondrial adenine nucleotide carrier (ANC), antagonized the effect of ZDV‐3P on mitochondrial swelling. Indeed, the IC50 value of ZDV‐3P increased from 3.0 to 17.4, 93.6 and 66.5 μM, in the presence of 20 μM, ADP, ATP or atractyloside, respectively.
ZDV‐3P did not displace [3H]‐ATP from its mitochondrial binding site(s) whereas ADP and atractyloside did, suggesting that ZDV‐3P and [3H]‐ATP do not share the same binding sites.
ZDV‐3P did not affect either mitochondrial respiration or ATP synthesis but inhibited Ca2+‐dependent mitochondrial swelling. It was concluded that mitochondrial toxic effects observed during the chronic administration of ZDV cannot be related to its active metabolite (ZDV‐3P).
Cellular mechanisms underlying carbachol‐induced oscillations of calcium‐dependent membrane current in smooth muscle cells from mouse anococcygeus
Authors: Wayman Christopher P , McFadzean Ian , Gibson Alan , Tucker John F 
Published: August 2006

At a holding potential of −40 mV, carbachol (50 μM) produced a complex pattern of inward currents in single smooth muscle cells freshly isolated from the mouse anococcygeus. Membrane currents were monitored by the whole‐cell configuration of the patch‐clamp technique. Previous work has identified the first, transient component as a calcium‐activated chloride current (ICl(Ca)) and the second sustained component as a store depletion‐operated non‐selective cation current (IDOC). The object of the present study was to examine the cellular mechanisms underlying the third component, a series of inward current oscillations (Ioscil) superimposed on IDOC.
Carbachol‐induced Ioscil (amplitude 97±11 pA; frequency 0.26±0.02 Hz) was inhibited by the chloride channel blocker anthracene‐9‐carboxylic acid (A‐9‐C; 1 mM), and by inclusion of 1 mM EGTA in the patch‐pipette filling solution.
In calcium‐free extracellular medium (plus 1 mM EGTA), carbachol produced an initial burst of oscillatory current which lasted 94 s before decaying to zero; Ioscil could be restored by re‐admission of calcium. The frequency, but not the amplitude, of Ioscil increased with increasing concentrations of extracellular calcium (0.5–10 mM).
Inclusion of the inositol triphosphate (IP3) receptor antagonist heparin (5 mg ml−1) in the patch‐pipette filling solution, or pretreatment of cells with the sarcoplasmic reticulum (SR) calcium ATPase inhibitor cyclopiazonic acid (CPA; 10 μM), prevented the activation of Ioscil by carbachol. Caffeine (10 mM) activated both ICl(Ca) and IDOC and prevented the induction of Ioscil by carbachol. Caffeine and CPA also abolished Ioscil in the presence of carbachol, as did both a low (3 μM) and a high (30 μM) concentration of ryanodine.
Carbachol‐induced Ioscil was abolished by the general calcium entry blocker SKF 96365 (10 μM) and by Cd2+ (100 μM), but was unaffected by La3+ (400 μM). As found previously, IDOC was also blocked by SKF 96365 and Cd2+, but not La3+; the inhibition of IDOC preceded the abolition of Ioscil by 27 s with SKF 96365 and by 30 s with Cd2+. Nifedipine (1 μM) produced a partial inhibition of the carbachol‐induced Ioscil frequency at holding potentials of −20 mV and −60 mV and, in addition, reduced IDOC at −60 mV by 18%.
It is concluded that carbachol‐induced inward current oscillations in mouse anococcygeus cells are due to a calcium‐activated chloride current, and reflect oscillatory changes in cytoplasmic calcium ion concentration. These calcium oscillations are derived primarily from the SR stores, but entry of calcium into the cell is necessary for store replenishment and maintenance of the oscillations. Capacitative calcium entry (via IDOC) appears to be important not only for sustained contraction of this tissue, but also as a route for re‐filling of the SR and, therefore, represents an important target for the development of novel and selective drugs.
Role of endothelium in regulation of smooth muscle membrane potential and tone in the rabbit middle cerebral artery
Authors: Yamakawa Nobutaka , Ohhashi Masuo , Waga Shiro , Itoh Takeo 
Published: August 2006

The characteristic features of the endothelium‐mediated regulation of the electrical and mechanical activity of the smooth muscle cells of cerebral arteries were studied by measuring membrane potential and isometric force in endothelium‐intact and ‐denuded strips taken from the rabbit middle cerebral artery (MCA).
In endothelium‐intact strips, histamine (His, 3–10 μM) and high K+ (20–80 mM) concentration‐dependently produced a transient contraction followed by a sustained contraction. Noradrenaline (10 μM), 5‐hydroxytryptamine (10 μM) and 9,11‐epithio‐11, 12‐methano‐thromboxane A2 (10 nM) each produced only a small contraction (less than 5% of the maximum K+‐induced contraction).
NG‐nitro‐L‐arginine (L‐NOARG, 100 μM), but not indomethacin (10 μM), greatly enhanced the phasic and the tonic contractions induced by His (1–10 μM) in endothelium‐intact, but not in endothelium‐denuded strips, suggesting that spontaneous or basal release of nitric oxide (NO) from endothelial cells potently attenuates the His‐induced contractions. Acetylcholine (ACh, 0.3–3 μM) caused concentration‐dependent relaxation (maximum relaxation by 89.7±7.5%, n=4, P<0.05) when applied to endothelium‐intact strips precontracted with His. L‐NOARG had little effect on this ACh‐induced relaxation (n=4; P<0.05). Apamin (0.1 μM), but not glibenclamide (3 μM), abolished the relaxation induced by ACh (0.3–3 μM) in L‐NOARG‐treated strips (n=4, P<0.05).
In endothelium‐intact tissues, His (3 μM) depolarized the smooth muscle membrane potential (by 4.4±1.8 mV, n=12, P<0.05) whereas ACh (3 μM) caused membrane hyperpolarization (−20.9±3.0 mV, n=25, P<0.05). The ACh‐induced membrane hypepolarization persisted after application of L‐NOARG (−23.5±5.9 mV, n=8, P<0.05) or glibenclamide (−20.6±5.4 mV, n=5, P<0.05) but was greatly diminished by apamin (reduced to −5.8±3.2 mV, n=3, P<0.05).
Sodium nitroprusside (0.1–10 μM) did not hyperpolarize the smooth muscle cell membrane potential (0.2±0.3 mV, n=4, P>0.05) but it greatly attenuated the His‐induced contraction in endothelium‐denuded strips (n=4, P<0.05).
These results suggest that, under the present experimental conditions: (i) spontaneous or basal release of NO from endothelial cells exerts a significant negative effect on agonist‐induced contractions in rabbit MCA, and (ii) ACh primarily activates the release of endothelium‐derived hyperpolarizing factor (EDHF) in rabbit MCA.
Effects of extracellular pH on agonism and antagonism at a recombinant P2X2 receptor
Authors: King B F , Wildman S S , Ziganshina L E , Pintor J , Burnstock G 
Published: August 2006

Under voltage‐clamp conditions, the activity of agonists and antagonists at a recombinant P2X2 receptor expressed in Xenopus oocytes was examined at different levels of extracellular pH (pHe).
In normal Ringer (Mg2+ ions absent), the amplitude of submaximal inward currents to ATP was increased by progressively lowering pHe (8.0–5.5). ATP‐responses reached a maximum at pH 6.5 with a 5 fold increase in ATP‐affinity; the apparent pKa was 7.05±0.05.
Receptor affinity for ATP was lowered when extracellular Ca2+ ions were replaced with equimolar Mg2+ ions. However, the amplitude of the ATP‐responses was still enhanced under acidic conditions, reaching maximal activity at pH 6.5 with a 5 fold increase in ATP‐affinity; the apparent pKa was 7.35±0.05.
ATP species present in the superfusate (for the above ionic conditions and pH levels) were calculated to determine the forms of ATP which activate P2X2 receptors: possible candidates include HATP, CaHATP and MgHATP. However, levels of these protonated species increase below pH 6.5, suggesting that receptor protonation rather than agonist protonation is more important.
The potency order for agonists of P2X2 receptors was: ATP>2‐MeS‐ATPATPγS> ATPαS>>CTPBzATP, while other nucleotides were inactive. EC50 and nH values for full agonists were determined at pH 7.4 and re‐examined at pH 6.5. Extracellular acidification increased the affinity by approximately 5 fold for full agonists (ATP, 2‐MeSATP, ATPγS and ATPαS), without altering the potency order.
The potency order for antagonists at P2X2 receptors was: Reactive blue‐2>trinitrophenol‐ATPPalatine fast blackCoomassie brilliant bluePPADS>suramin (at pH 7.4). IC50 values and slopes of the inhibition curves were re‐examined at different pH levels. Only blockade by suramin was affected significantly by extracellular acidification (IC50 values: 10.4±2 μM, at pH 7.4; 78±5 nM, at pH 6.5; 30±6 nM, at pH 5.5).
In summary, a lowered pHe enhanced the activity of all agonists at P2X2 receptors but, with the exception of suramin, not antagonists. Since a lowered pHe is also known to enhance agonist activity at P2X receptors on sensory neurones containing P2X2 transcripts, the sensitization by metabolic acidosis of native P2X receptors containing P2X2 subunits may have a significant effect on purinergic cell‐to‐cell signalling.
Pharmacological properties of the Ca2+‐release mechanism sensitive to NAADP in the sea urchin egg
Authors: Genazzani A A , Mezna M , Dickey D M , Michelangeli F , Walseth T F , Galione A 
Published: August 2006

The sea urchin egg homogenate is an ideal model to characterize Ca2+‐release mechanisms because of its reliability and high signal‐to‐noise‐ratio. Apart from the InsP3‐ and ryanodine‐sensitive Ca2+‐release mechanisms, it has been recently demonstrated that this model is responsive to a third independent mechanism, that has the pyridine nucleotide, nicotinic acid adenine dinucleotide phosphate (NAADP), as an endogenous agonist.
The sea urchin egg homogenate was used to characterize the pharmacological and biochemical characteristics of the novel Ca2+‐releasing agent, NAADP, compared to inositol trisphosphate (InsP3) and cyclic ADP ribose (cyclic ADPR), an endogenous activator of ryanodine receptors.
NAADP‐induced Ca2+‐release was blocked by L‐type Ca2+‐channel blockers and by Bay K 8644, while InsP3‐ and cyclic ADPR‐induced Ca2+‐release were insensitive to these agents. L‐type Ca2+‐channel blockers did not displace [32P]‐NAADP binding, suggesting that their binding site was different. Moreover, stopped‐flow kinetic studies revealed that these agents blocked NAADP in a all‐or‐none fashion.
Similarly, a number of K+‐channel antagonists blocked NAADP‐induced Ca2+‐release selectively over InsP3‐ and cyclic ADPR‐induced Ca2+‐release. Radioligand studies showed that these agents were not competitive antagonists.
As has been shown for InsP3 and ryanodine receptors, NAADP receptors were sensitive to calmodulin antagonists, suggesting that this protein could be a common regulatory feature of intracellular Ca2+‐release mechanisms.
The presence of K+ was not essential for NAADP‐induced Ca2+‐release, since substitution of K+ with other monovalent cations in the experimental media did not significantly alter Ca2+ release by NAADP. On the contrary, cyclic ADPR and InsP3‐sensitive mechanisms were affected profoundly, although to a different extent depending on the monovalent cation which substituted for K+. Similarly, modifications of the pH in the experimental media from 7.2 to 6.7 or 8.0 only slightly affected NAADP‐induced Ca2+‐release. While the alkaline condition permitted InsP3 and cyclic ADPR‐induced Ca2+‐release, the acidic condition completely hampered both Ca2+‐release mechanisms.
The present results characterize pharmacologically and biochemically the novel Ca2+‐release mechanism sensitive to NAADP. Such characterization will help future research aimed at understanding the role of NAADP in mammalian systems.
Characterization of α2‐adrenoceptors mediating contraction of dog saphenous vein: identity with the human α2A subtype
Authors: MacLennan S. J. , Luong L. A. , Jasper J. R. , To Z. P. , Eglen R. M. 
Published: August 2006

In the dog saphenous vein α1‐ and α2‐adrenoceptors mediate noradrenaline‐induced contractions in vitro. In order to study the α2‐adrenoceptor in isolation, α1‐adrenoceptors were inactivated by treatment of tissues with the alkylating agent phenoxybenzamine (3.0 μM for 30 min) in the presence of rauwolscine (1 μM) to protect α2‐adrenoceptors.
Noradrenaline‐induced contractions of tissues treated with phenoxybenzamine were antagonized competitively by the selective α2‐adrenoceptor antagonist rauwolscine, pKB=8.63±0.07 (means±s.e.mean; n=3), consistent with an interaction at α2‐adrenoceptors.
Noradrenaline was a full agonist at α2‐adrenoceptors in dog saphenous vein. By use of the method of partial receptor alkylation and analysis of concentration‐effect curve data by direct, operational model fitting methods, the affinity (pKA) and efficacy (τ) were 5.74±0.07 and 7.50±1.05, respectively (n=6). Nine other agonists which were examined each had affinities higher than noradrenaline, but with the exception of the imidazoline, A‐54741 (5,6‐dihydroxy‐1,2,3,4‐tetrahydro‐1‐naphthyl‐imidazoline) had relatively lower efficacies.
To compare the α2‐adrenoceptor in dog saphenous vein to the human recombinant subtypes, the affinities of twenty‐one compounds were estimated in functional studies in the dog saphenous vein and in radioligand binding studies for the human α2A, α2B and α2C receptor subtypes expressed in Chinese hamster lung (CHL) cells.
Of twenty‐one compounds examined in ligand binding studies, only nine had greater than ten fold selectivity for one human receptor subtype over either of the other two. These compounds were A‐54741, oxymetazoline, guanfacine, guanabenz, prazosin, spiroxatrine, tolazoline, WB 4101 and idazoxan. In dog saphenous vein, their affinities (pKA and pKB for agonists and antagonists respectively) were: A‐54741 (pKA=8.03±0.05), oxymetazoline (pKA=7.67±0.09), guanfacine (pKA=6.79±0.03); guanabenz (pKA=7.02±0.13); prazosin (pKB=5.19±0.08), spiroxatrine (pKB=6.59±0.04), tolazoline (pKB=6.21±0.07), WB 4101 (pKB=7.42±0.09) and idazoxan (pKB=7.11±0.08).
Comparisons of affinity estimates for these nine compounds at the receptor in dog saphenous vein and at the human recombinant subtypes suggest that the vascular receptor is most similar to the h α2A subtype; correlation coefficients (r) were 0.82 (h α2A), 0.24 (h α2B) and 0.04 (h α2C).

British Journal of Pharmacology (1997) 121, 1721–1729; doi:10.1038/sj.bjp.0701296
Contribution of phosphodiesterase isozymes to the regulation of the L‐type calcium current in human cardiac myocytes
Authors: Kajimoto Katsuya , Hagiwara Nobuhisa , Kasanuki Hiroshi , Hosoda Saichi 
Published: August 2006

To determine the contribution of the various phosphodiesterase (PDE) isozymes to the regulation of the L‐type calcium current (ICa(L)) in the human myocardium, we investigated the effect of selective and non‐selective PDE inhibitors on ICa(L) in single human atrial cells by use of the whole‐cell patch‐clamp method. We repeated some experiments in rabbit atrial myocytes, to make a species comparison.
In human atrial cells, 100 μM pimobendan increased ICa(L) (evoked by depolarization to +10 mV from a holding potential of −40 mV) by 250.4±45.0% (n=15), with the concentration for half‐maximal stimulation (EC50) being 1.13 μM. ICa(L) was increased by 100 μM UD‐CG 212 by 174.5±30.2% (n=10) with an EC50 value of 1.78 μM in human atrial cells. These two agents inhibit PDE III selectively.
A selective PDE IV inhibitor, rolipram (1–100 μM), did not itself affect ICa(L) in human atrial cells. However, 100 μM rolipram significantly enhanced the effect of 100 μM UD‐CG 212 on ICa(L) (increase with UD‐CG 212 alone, 167.9±33.9, n=5; increase with the two agents together, 270.0±52.2%; n=5, P<0.05). Rolipram also enhanced isoprenaline (5 nM)‐stimulated ICa(L) by 52.9±9.3% (n=5) in human atrial cells.
In rabbit atrial cells, ICa(L) at +10 mV was increased by 22.1±9.0% by UD‐CG 212 (n=10) and by 67.4±12.0% (n=10) by pimobendan (each at 100 μM). These values were significantly lower than those obtained in human atrial cells (P<0.0001). Rolipram (1–100 μM) did not itself affect ICa(L) in rabbit atrial cells. However, ICa(L) was increased by 215.7±65.2% (n=10) by the combination of 100 μM UD‐CG 212 and 100 μM rolipram. This value was almost 10 times larger than that obtained for the effect of 100 μM UD‐CG 212 alone.
These results imply a species difference: in the human atrium, the PDE III isoform seems dominant, whereas PDE IV may be more important in the rabbit atrium for regulating ICa(L). However, PDE IV might contribute significantly to the regulation of intracellular cyclic AMP in human myocardium when PDE III is already inhibited or when the myocardium is under β‐adrenoceptor‐mediated stimulation.

British Journal of Pharmacology (1997) 121, 1549–1556; doi:10.1038/sj.bjp.0701297
Differential effects of lovastatin on mitogen induced calcium influx in human cultured vascular smooth muscle cells
Authors: Clunn G. F. , Lymn J. S. , Schachter M , Hughes A. D. 
Published: August 2006

In this study the effect of lovastatin, an inhibitor of cholesterol and isoprenoid synthesis, on the rises in intracellular calcium concentration ([Ca2+]i) induced by platelet derived growth factor BB (PDGF‐BB), angiotensin II (AII), low density lipoproteins (LDL) and foetal calf serum (FCS) was examined in human cultured vascular smooth muscle cells (VSMC) from saphenous vein. Changes in [Ca2+]i were measured in cell suspensions by the Ca2+ sensitive probe, fura 2.
Incubation with lovastatin for 24–26 h markedly reduced the peak rise and sustained phase of [Ca2+]i elevation in response to PDGF‐BB but the responses to AII, LDL and FCS were unaffected. Further experiments showed that lovastatin pretreatment inhibited PDGF‐BB induced Ca2+ influx but not intracellular Ca2+ release. This inhibition could be overcome by co‐incubation with mevalonic acid.
Pretreatment of cells with the heterotrimeric G protein inhibitor pertussis toxin for up to 24 h completely abolished AII‐induced [Ca2+]i rises but the response to PDGF‐BB was unaffected.
The tyrosine kinase inhibitor genistein largely abolished PDGF‐BB‐induced [Ca2+]i elevation but had no significant effect on AII‐induced responses.
Pre‐incubation with lovastatin had no effect on the level of tyrosine phosphorylation of PDGF‐β receptors (as measured by Western blot) in response to the PDGF‐BB ligand.
PDGF‐BB elicits Ca2+ influx via a tyrosine kinase‐dependent mechanism distinct from the heterotrimeric G protein coupled pathway utilized by AII. Lovastatin most likely acts by inhibition of isoprenylation (via blockade of isoprenoid synthesis) of an intermediate molecule involved in PDGF‐BB‐induced Ca2+ influx.

British Journal of Pharmacology (1997) 121, 1789–1795; doi:10.1038/sj.bjp.0701299