bluuebunny/crossref_metadata_2025 huggingface dataset:
Involvement of platelet cyclic GMP but not cyclic AMP suppression in leukocyte‐dependent platelet adhesion to endothelial cells induced by platelet‐activating factor in vitro
Authors: Hirafuji Masahiko , Nezu Akihiro , Shinoda; Hisashi , Minami Masaru
Published: July 2012

Incubation of endothelial cells with platelets in the absence or the presence of PAF (10 μm) markedly increased platelet cyclic AMP levels, which were significantly decreased by indomethacin (3 μm). Co‐incubation of endothelial cells and platelets with polymorphonuclear leukocytes (PMNs) did not change the platelet cyclic AMP levels.

Incubation of endothelial cells with platelets in the absence of PAF increased platelet cyclic GMP levels, which were increased 3.5 fold by PAF. These cyclic GMP levels were significantly decreased by NG‐nitro‐L‐arginine (100 μm), and completely by methylene blue (10 μm). When endothelial cells and platelets were co‐incubated with PMNs, the cyclic GMP level in the cell mixture was 42.5 and 65.3% lower than that in endothelial cells and platelets without and with PAF stimulation, respectively.

PAF induced platelet adhesion to endothelial cells only when PMNs were present. Methylene blue dose‐dependently potentiated the PMN‐dependent platelet adhesion induced by PAF, although it had no effect in the absence of PMNs.

Sodium nitroprusside and 8‐bromo cyclic GMP but not dibutyryl cyclic AMP significantly, although partially, inhibited the platelet adhesion. Inhibition of cyclic GMP‐specific phosphodiesterase by zaprinast slightly inhibited the PMN‐induced platelet adhesion and potentiated the inhibitory effect of 8‐bromo cyclic GMP, while these drugs markedly inhibited the adhesion of platelet aggregates induced by PMN sonicates.

These results suggest that the impairment by activated PMNs of EDRF‐induced platelet cyclic GMP formation is involved in part in the mechanism of PMN‐dependent platelet adhesion to endothelial cells induced by PAF in vitro. The precise mechanism still remains to be clarified.
Structure activity studies of mast cell activation and hypotension induced by neuropeptide Y (NPY), centrally truncated and C‐terminal NPY analogues
Authors: Cross L.J. Mark , Beck‐Sickinger Annette G. , Bienert Michael , Gaida Wolfram , Jung Günther , Krause Eberhard , Ennis Madeleine
Published: July 2012

Neuropeptide‐induced histamine release is thought to occur via receptor‐independent mechanisms, with net charge and lipophilicity being important factors.

In this study, the histamine releasing ability of neuropeptide Y (NPY), two C‐terminal segments of NPY and 13 centrally truncated NPY analogues was examined. These results were compared with the ability of the peptides to bind to the Y2 receptor in the rabbit kidney membrane model and with their hypotensive actions in the anaesthetized‐rat model.

All analogues tested, with the exception of [Glu4,25,33,35]‐NPY(1–4)‐Ahx‐(25–36) and [Asp4,25,33,35]NPY(1–4)‐Ahx‐(25–36) which were devoid of histamine releasing activity, evoked a dose‐dependent histamine release but there were marked differences between the peptides. The native peptide was the least active.

Histamine release was not linked to the ability of the peptides to displace NPY from Y2 receptors. There was a statistical correlation between the hypotensive effects expressed as ED10 values (μmol kg−1, which induced a blood pressure decrease of 10 mmHg) and the EC25 for histamine release (r = 0.62, P = 0.04), although histamine release may not be the sole determinant of the alterations in blood pressure.

There was a strong negative correlation between EC25 for histamine release and net positive charge (r = −0.93, P = 5.7 × 10−7), i.e. increasing the net positive charge caused greater histamine release. However, there was a 12 fold difference in activity amongst the most positively charged analogues (+ 5). Helicity did not correlate with histamine releasing ability.

In the development of NPY‐related drugs the avoidance of compounds with net positive charge is recommended.
A study of tolerance to apomorphine
Authors: Montastruc Jean‐Louis , Llau Marie‐Elise , Senard Jean‐Michel , Tran Marie‐Antoinette , Rascol Olivier , Montastruc Paul
Published: July 2012

The present study was designed to investigate tolerance to several pharmacological effects of apomorphine.

Changes in blood pressure, heart rate, plasma noradrenaline levels, rectal temperature, respiratory rate and retching plus vomiting were compared after administration of apomorphine (200 μg kg−1, i.v. as a bolus) or saline at different time intervals (30, 120 and 720 min) in four groups of chloralose‐anaesthetized dogs.

The first administration of apomorphine induced a significant decrease in blood pressure and rectal temperature, a marked rise in heart rate with no change in noradrenaline plasma levels or respiratory rate. Emesis occurred in 71% of the animals.

A second administration of apomorphine 30 min later failed to modify blood pressure or heart rate. In contrast, the magnitude of apomorphine‐induced changes in blood pressure and heart rate was similar to that observed after the first administration when apomorphine was given 120 or 720 min later.

The apomorphine‐induced decrease in rectal temperature evoked by a second dose of apomorphine was less marked when given 30 and 120 min after the first dose and unchanged when given 720 min later.

The number of animals exhibiting retching and vomiting was lower when apomorphine was reinjected after 30 min than when the time between two successive injections of apomorphine was 120 or 720 min.

These results show that tolerance to apomorphine involves its cardiovascular, hypothermic and emetic effects. The time course of tolerance to repeated injections of apomorphine is longer for its hypothermic than for its hypotensive or emetic effects. This suggests a tissue‐specific regulation of D2 dopamine receptors to repeated injections of apomorphine.
Effects of trimetazidine on pHi regulation in the rat isolated ventricular myocyte
Authors: Lagadic‐Gossmann Dominique , Le Prigent Karine , Feuvray Danielle
Published: July 2012

We have examined the effects of trimetazidine (TMZ) on intracellular pH (pHi) regulation in rat isolated ventricular myocytes. pHi was recorded ratiometrically by use of the pH‐sensitive fluoroprobe, carboxy‐SNARF‐1 (carboxy‐seminaphtorhodafluor).

Following an intracellular acid load (induced by 10 mM NH4Cl removal), pHi recovery in HEPES‐ buffered Tyrode solution was significantly slowed down upon application of 0.3 mM TMZ only when myocytes were pretreated for 5 h 30 min (slowing by ∼ 50%; P < 0.01). This effect of TMZ on pHi recovery was shown to be not only time‐ but also dose‐dependent with a large, quickly reversible, effect obtained with 1 mM TMZ applied for 2–3 h (slowing by ∼ 64%; P 0.001). This slowing of pHi recovery was also associated with a decrease of the NH4+ removal‐induced acidification.

Relationship between intracellular intrinsic buffering power (βi) and pHi was assessed in absence or presence of TMZ (0.3 mM or 1 mM). As expected, βi increased roughly linearly with a decrease in pHi in all cases. However, both concentrations of TMZ significantly increased βi (by ∼ 55 and 65% at pHi 7.1, respectively).

When Na+/H+ exchange was inhibited by dimethyl amiloride (DMA; 40 μm), trimetazidine (1 mM) did not change the H+ flux estimated at pHi 7.1 (0.31 ± 0.03 mequiv 1−1 min−1, n = 5, control, versus 0.30 ± 0.025 mequiv 1−1 min−1, n = 5, TMZ), ruling out any effect of TMZ on background acid loading.

Acid efflux carried by Na+/H+ exchange was significantly decreased only when myocytes were pretreated with 1 mM TMZ, for 2–3 h (JeH = 2.86 ± 0.38 mequiv 1−1 min−1, n = 26, control, versus 1.66 ± 0.26 mequiv 1−1 min−1, n = 10, TMZ, estimated at pHi 7.1; P < 0.05).

In conclusion, the present work demonstrates that, following an intracellular acid load in HEPES‐ buffered medium, trimetazidine slows down pHi recovery in rat isolated ventricular myocytes, primarily through an increase of βi. An effect on Na+/H+ exchange is also detected but only after long‐term incubation of the myocytes with TMZ.
The effects of purine compounds on the isolated aorta of the frog Rana temporaria
Authors: Knight Gillian E. , Burnstock Geoffrey
Published: July 2012

In the isolated aorta of the frog, Rana temporaria, adenosine concentration‐dependently, endothelium‐independently relaxed adrenaline pre‐constricted vessels. None of the adenosine analogues including D‐5′‐(N‐ethylcarboxamide) adenosine (NECA), R‐ and S‐N6‐(2‐phenylisopropyl) adenosine (R‐and S‐PIA) and 2‐chloroadenosine (2‐CA), or the more selective A1, A2 and A3 agonists cyclopentyladenosine (CPA), CGS 21680 and N6‐(3‐iodobenzyl) adenosine‐5′‐N‐methylcarboxamide (IB‐MECA) respectively, had any effect.

The non‐selective adenosine antagonist, 8‐p‐sulphophenyl‐theophylline (8‐pSPT; 30 μm) failed to inhibit adenosine relaxations, as did NG‐nitro‐L‐arginine methyl ester (L‐NAME; 0.1 mM) and indomethacin (30 μm).

Adenosine 5′‐triphosphate (ATP), α,β‐methylene ATP (α,β‐MeATP), β,γ‐methylene ATP MeATP), 2‐methylthio ATP (2‐MeSATP) and uridine 5′‐triphosphate (UTP) all concentration‐dependently contracted the frog aorta. ATP and α,β‐MeATP were equipotent and more potent than UTP and β,γ‐MeATP; 2‐MeSATP had little activity.

The P2‐purinoceptor antagonist, suramin (0.1 mM) inhibited contractions to α,β‐MeATP but not to ATP. Pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS; 30 μm) also inhibited contractions to α,β‐MeATP but not to ATP. Contractions to ATP were, however, inhibited by indomethacin (30 μm).

In conclusion, in the frog aorta there appears to be a novel subclass of P1‐purinoceptor mediating vasodilatation, although like the A3 subclass it is not blocked by methylxanthines; a P2‐purinoceptor mediates vasoconstriction which resembles a P2X subtype, based on the agonist potency of α,β‐MeATP being more potent than 2‐MeSATP (UTP has moderate activity) and PPADS is an effective antagonist. There is no evidence for the presence of a P2Y‐purinoceptor, mediating vasodilatation, in this preparation.
Binding sites for α‐trinositol (inositol 1,2,6‐trisphosphate) in porcine tissues; comparison with Ins(1,4,5)P3 and Ins(1,3,4,5)P4‐binding sites
Authors: Stricker Rolf , Westerberg Eva , Reiser Georg
Published: July 2012

The molecular mechanism of action of the inositol trisphosphate isomer, α‐trinositol (Ins(1,2,6)P3) which has potential therapeutic use in treatment of inflammation and burn oedema, is still unclear. Therefore we have studied binding sites for α‐trinositol in different tissues.

In membranes from pig cerebellum, liver, kidney, heart, and spleen, the density of specific [3H]‐α‐trinositol binding sites was maximal at pH 5.0. Cerebellum and spleen showed only one binding site (cerebellum KD = 9.1 μm, spleen KD = 7.3 μm). In the other tissues, there were a high‐affinity site (heart KD = 70 nM, liver KD = 790 nM and kidney KD = 1800 nM), besides a low‐affinity site with a KD ranging between 32 and 120 μm. In cerebellar membranes, the affinity and density (107 pmol mg−1 protein) of α‐trinositol binding sites were not affected by phosphate (0 to 25 mM).

Binding of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 to membranes from different porcine tissues was also determined. Ins(1,3,4,5)P4, the isomer stereochemically related to α‐trinositol, binds with an affinity of 1.2 nM in cerebellum, but in the other tissues the binding site density was too low to determine the affinity. With cerebellar membranes heterologous displacement of [3H]‐Ins(1,3,4,5)P4 by α‐trinositol yielded a K1 of 11 μm. The Ins(1,4,5)P3 receptor displayed an affinity of 15 nM in cerebellum and of 5 to 7 nM in the other tissues investigated.

The solubilized Ins(1,3,4,5)P4 receptor preparation from cerebellum did not show Ins(1,2,6)P3 binding. Ins(1,2,6)P3 binding was found in the pellet obtained after solubilization of the membranes with the detergent Brij 58.

Thus, in different tissues α‐trinositol binds to proteins with different affinity. They are obviously not related to binding sites for Ins (1,4,5)P3 or for Ins(1,3,4,5)P4. Future experiments have to unravel the identity of the binding protein(s) for α‐trinositol.
Characterization of putative 5‐ht7 receptors mediating direct relaxation in Cynomolgus monkey isolated jugular vein
Authors: Leung E. , Walsh L.K.M. , Pulido‐Rios M.T. , Eglen R.M.
Published: July 2012

5‐Hydroxytryptamine (5‐HT) receptors mediating contraction and relaxation are present in Cynomolgus monkey isolated jugular vein denuded of endothelium.

In the absence of spasmogen, α‐methyl‐5‐HT and sumatriptan contracted the tissues with potency values (pEC50) of 6.8 (n=2) and 6.4 ± 0.1 (mean ± s.e. mean, n=3), respectively. In contrast, 5‐HT caused an initial contraction (10 nM‐1 μm), followed by relaxation (1 μm‐32 μm). The contractile effect of α‐methyl‐5‐HT was antagonized by ketanserin with a pKB value of 8.1 (n=2). 5‐Carboxamidotryptamine (5‐CT), 5‐methoxytryptamine (5‐MeOT) and 8‐OH‐DPAT did not contract or relax the tissues in the absence of spasmogen.

In tissues precontracted with U46619 (10 nM) and in the presence of 5‐HT1A, 5‐HT1B, 5‐HT2A, 5‐HT3, and 5‐HT4 receptor blockade, 5‐CT and 5‐MeOT caused endothelium‐independent relaxation with potency values of 7.5±0.1 (n=21) and 5.7±0.1 (n=4), respectively. The potency of 5‐HT was 7.2 (n=2) while α‐methyl‐5‐HT did not start to relax the tissues below a concentration of 10 μm.

Relaxations elicited by 5‐CT were antagonized by the following compounds (with pKB values in parentheses): methiothepin (9.7), mesulergine (8.1), metergoline (8.0), clozapine (7.8), mianserin (7.7), spiperone (7.3), ritanserin (7.1), methysergide (7.0) and ketanserin (5.7).

It is concluded that the 5‐HT receptor mediating endothelium‐independent relaxation may be a functional correlate of the putative 5‐ht7 receptor.
Functional evidence of atypical β3‐adrenoceptors in the human colon using the β3‐selective adrenoceptor antagonist, SR 59230A
Authors: De Ponti Fabrizio , Gibelli Graziano , Croci Tiziano , Arcidiaco Massimo , Crema Francesca , Manara Luciano
Published: July 2012

The role of β3‐adrenoceptors in human colonic circular smooth muscle was assessed in vitro by use of the β2‐selective antagonist SR 59230A. Isoprenaline, in the presence of the selective β‐adrenoceptor antagonists CGP 20712A (β1) and ICI 118551 (β2), both at 0.1 μ, concentration‐dependently relaxed the preparation (pEC50 = 5.22). This effect was potently and competitively antagonized by SR 59230A with a pA2 of 8.31, while its R,R enantiomer SR 59483A gave an apparent pKB of 6.21. Relaxation was likewise produced by CGP 12177A (pEC50 = 6.05), but not by BRL 37344. Although only one of these β3‐selective agonists was effective, the remarkably high potency of SR 59230A as a stereospecific antagonist of non‐β1 non‐β2 relaxation of human colonic muscle by isoprenaline provides strong functional evidence of β3‐adrenoceptors in that tissue.
Endothelin‐1 and the periaqueductal gray area of the rat: an autoradiographic and functional pharmacological study
Authors: D'Amico Michele , Dashwood Michael R. , Warner Timothy D.
Published: July 2012

. Endothelin‐1 (ET‐1) injected centrally induces pressor effects and associated haemodynamic changes. Here we have evaluated the effects on systemic and regional cardiovascular parameters of injection of ET‐1 into the periaqueductal gray (PAG) area of anaesthetized rats. In addition, we have used the ETA receptor‐selective antagonist, FR 139317, the ETB receptor‐selective antagonist, BQ‐788, and the ETA/ ETB receptor non‐selective antagonist, SB 209670, to identify the receptor(s) mediating these effects. We have also used in vitro autoradiography to identify binding sites for ET‐1 in the PAG.

. In vitro autoradiography showed dense binding of [125I]‐PD 151242 (for ETA receptors) in the PAG area, with the binding sites being homogeneously distributed within the dorsal, lateral and ventral subregions. Tissues incubated with [125I]‐BQ 3020 (for ETB receptors) had little binding.

. Injection of ET‐1 (0.1, 1 and 10 pmol per rat) in the dorsolateral PAG area significantly increased, in a dose‐dependent manner the mean arterial blood pressure (MAP). The highest dose of ET‐1 (10 pmol) also decreased the heart rate by 18±1%, n=6 (P>0.05). Increases in blood pressure induced by ET‐1 (1 pmol; 31±6.6 mmHg, n=6) were greatly reduced by pre‐administration to the PAG area of FR 139317 (5 nmol per rat) or SB 209670 (3 nmol per rat) (97 and 94%, respectively), but were unaffected by BQ‐788 (5 nmol per rat). Similarly, FR 139317 and SB 209670 prevented the decrease in heart rate induced by ET‐1 while BQ‐788 did not affect it.

. Injection of ET‐1 to the PAG area caused falls in renal blood flow (RBF) as measured by an ultrasonic flow probe, and increased renal vascular resistance (RVR). Pre‐treatment of the PAG with FR 139317 or SB 209670, but not with BQ‐788, prevented this ET‐1‐induced effect.

. Injection of ET‐1 (10 pmol) also increased total peripheral resistance (TPR; control, 2.39±0.2 mmHg ml−1 min 100 g body weight) by 100±9% (n=5) and reduced the cardiac output (CO; control, 94.7±3.1 ml min−1) by 30±3% (n=5), as determined by radioactive microspheres. Vascular resistances were increased in other organs, such as skeletal muscle (88±5%, n=4), the colon (55±7%, n=4) and the stomach (47±3%, n=4). Pretreatment of the PAG area with FR 139317 or SB 209670 reduced the increases in TPR and vascular resistance, and the reduction in CO caused by ET‐1. BQ‐788 did not affect the responses to ET‐1.

. Thus, there are predominantly ETA binding sites within the PAG area and injection of ET‐1 into the PAG area causes complex haemodynamic changes which are sensitive to ETA receptor antagonism. ETA receptors are, therefore, the predominant mediators of the actions of ET‐1 in the PAG of the rat.
Relative potencies of metal ions on transmitter release at mouse motor nerve terminals
Authors: Porter V.A. , Wray D.
Published: July 2012

. The effects of a range of metal ions were systematically studied at the mouse neuromuscular junction in order to investigate the type of calcium channel present at the nerve terminal.

. Endplate potentials and miniature endplate potentials were recorded from the phrenic nerve diaphragm muscle preparation with glass microelectrodes.

. Endplate potential amplitudes and quantal contents were reduced by manganese (IC50 220 μm), cadmium (IC50 11 μm), cobalt (IC50 340 μm), and nickel (IC50 420 μm). Miniature endplate potentials were not affected by these ions at concentrations equal to the IC50S. Gadolinium did not reduce endplate potentials up to 100 μm.

. Comparisons made with known channel types in neuroblastoma cell lines suggest that the calcium channels at the motor nerve terminal are different from those types studied in the cell lines, although most similarity is shown to the high‐voltage activated calcium channel types.
Effects of delayed treatment with nafronyl oxalate on microsphere embolism‐induced changes in monoamine levels of rat brain regions
Authors: Takagi Norio , Miyake Keiko , Ohiwa Akiko , Nukaga Reiko , Takeo Satoshi
Published: July 2012

. The present study was undertaken to examine the effects of delayed treatment with nafronyl oxalate (nafronyl), a cerebral vasodilator, on monoamine neurotransmitters of brain regions in the microsphere‐embolized rat.

. Microsphere embolism was induced by injecting 900 microspheres with a diameter of 48 μm into the right internal carotid artery of rats. Microsphere‐embolized rats were treated with nafronyl, 15 mg kg−1, i.p., twice daily from the first to the 5th day. Levels of monoamines and their metabolites in the cerebral cortex, striatum, and hippocampus were measured on days 3 and 5 after the operation by a high‐performance liquid chromatograph with electrochemical detection. In vivo tyrosine or tryptophan hydroxylation was estimated by measurement of the accumulation of 3,4‐dihydroxyphenylalanine or 5‐ hydroxy‐1‐tryptophan after administration of 3‐hydroxybenzylhydrazine dihydrochloride, an inhibitor of aromatic L‐amino acid decarboxylase.

. Microsphere embolism induced decreases in dopamine, noradrenaline and 5‐hydroxytryptamine in three brain regions of the right hemisphere on days 3 and 5. In the left hemisphere, the monoamines were reduced, but to a lesser degree than in the right hemisphere. On days 3 and 5, the decrease in the monoamines of the right hemisphere was attenuated by nafronyl treatment except for noradrenaline on day 3. The decrease in the monoamines levels in the left hemisphere was almost completely prevented by nafronyl treatment.

. On day 3 after microsphere embolism, in vivo tyrosine and tryptophan hydroxylation was lower than the pre‐embolic value in all three brain regions. Treatment of the embolized rats with nafronyl significantly attenuated the decrease in in vivo tyrosine and tryptophan hydroxylation in the ipsilateral hemisphere, but not hippocampal tryptophan hydroxylation.

. The results suggested that treatment with nafronyl improves or attenuates changes in monoamine neurotransmitter metabolism of the brain regions impaired by microsphere embolism. The mechanisms underlying this effect may be attributed to preservation of the ability to synthesize monoamines when the brain is ischaemic or oligaemic.
Modulation of sexual behaviour in the rat by a potent and selective α2‐adrenoceptor antagonist, delequamine (RS‐15385‐197)
Authors: Tallentire D. , McRae G. , Spedding M. , Clark R. , Vickery B.
Published: July 2012

. The contributions of α2‐adrenoceptors and 5‐HT1A receptors to sexual behaviour in the rat have been re‐evaluated by use of a highly potent and selective α2‐adrenoceptor antagonist, delequamine (RS‐15385‐197), yohimbine, idazoxan and the partial agonist at 5‐HT1A receptors, 8‐hydroxy‐2(di‐n‐propylamino)‐ tetralin (8‐OH‐DPAT).

. In a model where naive male rats were introduced to oestrogen‐progesterone primed, sexually receptive female rats, delequamine (0.4–6.4 mg kg−1, p.o.) dose‐relatedly increased the sexual behaviour score over the entire dose‐range whereas yohimbine was effective at only one dose, 2 mg kg−1, p.o. Idazoxan was active only at 2.5 and 5 mg kg−1, p.o. Yohimbine, but neither delequamine nor idazoxan, decreased ejaculation latency. 8‐OH‐DPAT (0.1 and 0.25 mg kg−1, s.c.) reduced the time, and the number of intromissions to ejaculation without affecting other parameters. A combination of delequamine (0.4 mg kg−1, p.o.) and 8‐OH‐DPAT (0.1 mg kg−1 s.c.) increased the percentage of rats mounting, intromitting and ejaculating, and reduced ejaculation latency and the number of intromissions.

. In orchidectomized, sexually experienced rats exposed to sexually receptive females, delequamine, idazoxan and yohimbine increased the number of rats mounting, and there was a tendency to increase the number of animals intromitting, but no effect on ejaculatory behaviour.

. In ovariectomized female rats brought to low level receptivity by priming with low dose injections of oestradiol benzoate and progesterone, delequamine, at 1.6 and 6.4 mg kg−1 p.o., increased lordosis, while yohimbine, at 2, 4 and 8 mg kg−1 p.o., reduced lordotic responses to sexually experienced males in a dose‐dependent manner. 8‐OH‐DPAT at 0.1, 0.25 mg kg−1, s.c. reduced lordosis in a dose‐dependent manner.

. These findings may be explained on the basis that yohimbine is an α2‐adrenoceptor antagonist with affinity for 5‐HT1A receptors and that the effects of 5‐HT1A receptors may modulate the sexual behaviour responses to α2‐receptor antagonism in some models. Thus, in contrast to yohimbine, the highly‐selective α2‐adrenoceptor antagonist, delequamine, was very effective in increasing the behavioural score in male and female rats over a wide dose‐range.
Two types of ATP‐sensitive potassium channels in rat portal vein smooth muscle cells
Authors: Zhang H‐L. , Bolton T.B.
Published: July 2012

. Single‐channel recordings were made from single, enzymatically isolated smooth muscle cells of rat portal vein by the patch‐clamp technique.

. Unitary potassium currents were identified through two types of K‐channels with conductances in 60:130 mM K‐gradient of 50 and 22 pS; these are referred to as LK and MK channels respectively.

. The LK channels became extremely active if isolated patches were created into nucleotide‐free solution; activity was inhibited by ATP applied to the inner surface of the patch with a half maximal inhibition (Ki) of 11–23 μm. Channel activity declined and disappeared with time and could be regenerated by a brief application of Mg‐ATP or a nucleoside diphosphate such as UDP (in the presence of Mg). LK channel activity was rarely stimulated by levcromakalim and not by pinacidil (K‐channel openers, KCOs) but was blocked by glibenclamide.

. Activity of MK channels declined if isolated patches were created into nucleotide free solution; activity reappeared if UDP or ATP alone (in the presence of Mg) was applied; pinacidil or levcromakalim in the presence of ATP or UDP further increased channel activity which was blocked by glibenclamide.

. The LK channel inhibited by ATPi is very similar in its conductance and other properties to the KATP channel described in tissues other than smooth muscle, in its conductance and properties the MK channel resembles the KNDP channel we have previous described as present in other smooth muscles and opening in responses to KCOs.
Inhibition by lifarizine of intracellular Ca2+ rises and glutamate exocytosis in depolarized rat cerebrocortical synaptosomes and cultured neurones
Authors: Budd David C. , May Gillian R. , Nicholls David G. , McCormack James G.
Published: July 2012

. The effects of lifarizine (RS‐87476) on intracellular Ca2+ rises and the release of glutamate from rat cerebrocortical synaptosomes depolarized with 30 mM KCl were investigated by use of entrapped fura 2 and exogenous glutamate dehydrogenase.

. Prior (1 min) addition of lifarizine decreased 30 mM KCl‐induced total glutamate release, with 3 μm and 10μm causing 39% and 72% averaged decreases from controls. The calcium‐dependent component of glutamate release (approx. 40% of total) was similarly decreased by 47% and 74%, whereas the calcium‐independent component was decreased by only 32% and 43% respectively.

. In parallel experiments with fura‐2‐loaded synaptosomes, lifarizine reduced the depolarization‐induced increases in intracellular [Ca2+], suggesting that this is the means by which the decreases in glutamate release are brought about. Lifarizine inhibited both the plateau and the spike phases of the Ca2+ increases suggesting that, in addition to its known sodium channel blocking properties, it may also inhibit more than one class of calcium channel in the synaptosomes.

. Lifarizine at 1 μm and 3 μm also inhibited the rises in intracellular [Ca2+] in rat cultured cortical neurones depolarized with 60 mM KCl.

. These effects of lifarizine on intracellular Ca2+ and glutamate exocytosis may contribute to its neuroprotective action.
Nitric oxide synthase‐cyclo‐oxygenase pathways in organum vasculosum laminae terminalis: possible role in pyrogenic fever in rabbits
Authors: Lin Jju‐Home , Lin Mao‐Tsun
Published: July 2012

. Fever was induced in rabbits by administration of Escherichia coli endotoxin (lipopolysaccharide; LPS; 0.001–10 μ) into the organum vasculosum laminae terminalis (OVLT). Deep body temperature was evaluated over a period of 7 h.

. The LPS‐induced febrile response was mimicked by intra‐OVLT injection of the nitric oxide (NO) donors, S‐nitroso‐acetylpenicillamine (SNAP, 1–10 μ), sodium nitroprusside (SNP, 50 μ), or hydroxylamine (10 μ), the cyclic GMP analogue 8‐bromo‐cyclic GMP (8‐Br‐cyclic GMP, 10–100 μ), or prostaglandin E2 (PGE2, 0.2 μ).

. Dexamethasone (Dex, a potent inhibitor of the transcription of inducible NO synthase, iNOS, 10 μ), anisomycin (a protein synthesis inhibitor, 100 μ), L‐N5‐(1‐iminoethyl)ornithine (L‐NIO; an irreversible NOS inhibitor, 10–200 μ), aminoguanidine (a specific iNOS inhibitor, 1000 μ), or NG‐methyl‐L‐arginine acetate (L‐NMMA, a NOS inhibitor, 100 μ) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. An intra‐OVLT dose of 1000 μ of NG‐nitro‐L‐arginine methyl ester (L‐NAME, a potent inhibitor of constitutive NOS) did not exhibit antipyretic effects.

. Methylene blue (an inhibitor of NOS and soluble guanylate cyclase, 1–10 μ), 6‐(phenylamino)‐5,8‐quinolinedione (LY‐83583; an inhibitor of soluble guanylate cyclase and NO release, 20 μ), or indomethacin (an inhibitor of cyclo‐oxygenase, COX, 400 μ) inhibited fever induced by LPS when injected into the OVLT 1 h before LPS injection. Pretreatment with methylene blue or haemoglobin (a NO scavenger, 100 μ) attenuated the fever induced by intra‐OVLT injection of SNAP.

. The PGE2‐induced fever was potentiated, rather then attenuated, by pretreatment with an intra‐OVLT dose of animoguanidine (1000 μ), L‐NMMA (100 μ), or L‐NIO (200 μ).

. These results suggest that iNOS‐COX pathways in the OVLT represent an important mechanism for modulation of pyrogenic fever in rabbits.
Effects of β‐adrenoceptor antagonists on Ca2+‐overload induced by lysophosphatidylcholine in rat isolated cardiomyocytes
Authors: Chen Min , Hashizume Hiroko , Abiko Yasushi
Published: July 2012

The effects of β‐adrenoceptor antagonists including (−)− and (+)‐propranolol, (−)− and (+)‐penbutolol, timolol, pindolol, atenolol, acebutolol and practolol on the Ca2+‐overload induced by lysophosphatidylcholine (LPC) were examined in isolated cardiomyocytes of the rat.

Fura‐2 was used for measurement of the intracellular calcium concentration ([Ca2+]i). LPC (15 μm) produced a rapid increase in [Ca2+]i from 72±5 to 3042±431 nM which coincided with a decrease in the percentage of rod‐shaped cells from 69±2 to 5±2%.

Preincubation with (−)−propranolol (20 μm), (+)‐propranolol (50 μm), or (−)− or (+)‐penbutolol (20 μm), the lipophilicity of which is higher than other β‐adrenoceptor antagonists, significantly inhibited both the increase in [Ca2+]i and the cell‐shape change induced by 15 μm LPC. The inhibitory effects of the four drugs on the LPC‐induced increase in [Ca2+]i and cell‐shape change were concentration‐dependent. The IC50s of (−)−propranolol, (+)‐propranolol, (−)− and (+)‐penbutolol for the increase in [Ca2+]i were 1.28, 10.50, 0.67 and 0.76 μm, respectively.

Pretreatment with pindolol, timolol, acebutolol, practolol, atenolol or lignocaine did not inhibit the increase in [Ca2+]i and the morphological change induced by LPC.

LPC markedly increased the release of creatine phosphokinase from 9±1 to 45±2% which could be significantly reduced by (−)− or (+)‐propranolol but not by acebutolol or timolol.

The protective effects of (−)− and (+)‐propranolol, (−)− and (+)‐penbutolol against the Ca2+‐overload induced by LPC were not associated with the β‐adrenoceptor antagonistic action, but probably with an unknown action which is related to the preservation of membrane integrity. Further studies are necessary to clarify the exact mechanisms of the protective action of these β‐adrenoceptor antagonists against the Ca2+‐overload induced by LPC.
Respective degree of expression of β1, β2‐ and β3‐adrenoceptors in human brown and white adipose tissues
Authors: Deng Chengjun , Paoloni‐Giacobino Ariane , Kuehne Françoise , Boss Olivier , Revelli Jean‐Pierre , Moinat Madelaine , Cawthorne Michael A. , Muzzin Patrick , Giacobino Jean‐Paul
Published: July 2012

The possible existence of a β3‐adrenoceptor in human brown and white adipose tissues was investigated by mRNA expression and binding studies.

The relative amounts of β1‐, β2‐ and β3‐adrenoceptor mRNA, as determined by total RNA Northern blot analysis in newborn brown adipose tissue, were 28, 63 and 9% respectively of the total β‐adrenoceptor mRNA.

The β1/β2‐adrenoceptors of human brown adipose tissue plasma membranes were characterized using [3H]‐CGP 12177 as a ligand. Their Kd and Bmax values were 1.9 nM and 156 fmol mg−1 of membrane proteins, respectively. The β3‐adrenoceptor was characterized by use of the new specific radioligand [3H]‐SB 206606. The binding of this ligand was stereospecifically displaced by the active R, R‐ or the inactive S, S‐enantiomer of BRL 37344 up to a concentration of about 10 μm. The Kd and Bmax values of the brown adipose tissue membrane β3‐adrenoceptors were 87 nM and 167 fmol mg−1 of proteins, respectively. A low affinity [3H]‐CGP 12177 binding site population was also detected in these membranes.

In human omental white adipose tissue, no β3‐adrenoceptor mRNA could be detected in total RNA Northern blots and the β1‐ and β2‐adrenoceptor mRNAs represented 9 and 91%, respectively of the total β‐adrenoceptor mRNA, and no specific binding of [3H]‐SB 206606 could be measured.
Characterization of a P2X‐purinoceptor in cultured neurones of the rat dorsal root ganglia
Authors: Robertson S.J. , Rae M.G. , Rowan E.G. , Kennedy C.
Published: July 2012

The electrophysiological actions of the P2‐purinoceptor agonists, adenosine 5′‐triphosphate (ATP), 2‐methylthioATP (2‐meSATP) and α, β‐methyleneATP (α, β‐meATP) and of uridine 5′‐triphosphate (UTP) were studied under concentration and voltage‐clamp conditions in dissociated neurones of 1–6 day old rat dorsal root ganglia.

ATP (10 nM‐100 μm) applied rapidly via a U‐tube perfusion system (equilibration time > 10 ms) activated concentration‐dependent inward currents with a latency to onset of a few ms, an EC50of 719 nM and a Hill slope of 1.47.

2‐meSATP (10 nM‐100 μm) and α, μ‐meATP (100 nM‐100 μm) also evoked transient inward currents. The EC50and Hill slopes were 450 nM and 1.58 for 2‐meSATP and 1.95 μmand 1.53 for α, μ‐meATP respectively. There was no significant difference between the maximum currents evoked by the three agonists.

As the concentration of ATP increased so the rate of rise and decay of the currents also increased. At 100 and 300 nM ATP the decay of the current was best fitted by a single exponential, but at 1 μmand above two exponentials were required. Log‐log plots of the rise time or time constants of decay versus concentration were linear. Currents evoked by 2‐meSATP and α, μ‐meATP showed a similar concentration‐dependence in their kinetics.

Inward currents evoked by ATP, 2‐meSATP and α, μ‐meATP (300 nM) were abolished by the P2‐purinoceptor antagonist, suramin (100 μm).

UTP (10 μm) evoked similar transient inward currents, which were sensitive to suramin (100 μm). ATP (10 μm), applied 2 min beforehand, reduced the response to UTP (10 μm) by 80 ± 10%.

This study shows that ATP, 2‐meSATP and α, μ‐meATP act via a suramin‐sensitive P2X‐purinoceptor to evoke rapid, transient inward currents in dissociated neurones of rat dorsal root ganglia. The pyrimidine nucleotide, UTP, was also active. It is likely that the agonists were acting at the P2X3‐subtype to produce these effects.
Pharmacological characterization of metabotropic glutamate receptors coupled to phospholipase D in the rat hippocampus
Authors: Pellegrini‐Giampietro Domenico E. , Torregrossa Serenella Albani , Moroni Flavio
Published: July 2012

Phospholipase D (PLD) is the key enzyme in a signal transduction pathway leading to the formation of the second messengers phosphatidic acid and diacylglycerol. In order to define the pharmacological profile of PLD‐coupled metabotropic glutamate receptors (mGluRs), PLD activity was measured in slices of adult rat brain in the presence of mGluR agonists or antagonists. Activation of the phospholipase C (PLC) pathway by the same agents was also examined.

The mGluR‐selective agonist (1S, 3R)‐1‐aminocyclopentane‐1, 3‐dicarboxylic acid [(1S, 3R)‐ACPD] induced a concentration‐dependent (10–300 μm) activation of PLD in the hippocampus, neocortex, and striatum, but not in the cerebellum. The effect was particularly evident in hippocampal slices, which were thus used for all subsequent experiments.

The rank order of potencies for agonists stimulating the PLD response was: quisqualate > ibotenate > (2S, 3S, 4S)‐α‐(carboxycyclopropyl)‐glycine > (1S, 3R)‐ACPD > L‐cysteine sulphinic acid > L‐aspartate > L‐glutamate. L‐(+)‐2‐Amino‐4‐phosphonobutyric acid and the ionotropic glutamate receptor agonists N‐methyl‐D‐aspartate, α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid, and kainate failed to activate PLD. (RS)‐3, 5‐dihydroxyphenylglycine (100–300 μm), an agonist of mGluRs of the first group, stimulated PLC but inhibited the PLD response elicited by 100 μm (1S, 3R)‐ACPD.

(+)‐α‐Methyl‐4‐carboxyphenylglycine (0.1‐1 mM), a competitive antagonist of mGluRs of the first and second group, elicited a significant PLD response. L‐(+)‐2‐Amino‐3‐phosphonopropionic acid (1 mM), an antagonist of mGluRs of the first group, inhibited the 100 μm (1S, 3R)‐ACPD‐induced PLC response but produced a robust stimulation of PLD.

12‐O‐Tetradecanoylphorbol 13‐acetic acid and phorbol 12, 13‐dibutyrate (PDBu), activators of protein kinase C, at 1 μm had a stimulatory effect on mGluRs linked to PLD but depressed (1S, 3R)‐ACPD‐induced phosphoinositide hydrolysis. The protein kinase C inhibitor, staurosporine (1 and 10 μm) reduced PLD activation induced by 1 μm PDBu but not by 100 μm (1S, 3R)‐ACPD.

Our results suggest that PLD‐linked mGluRs in rat hippocampus may be distinct from any known mGluR subtype coupled to PLC or adenylyl cyclase. Moreover, they indicate that independent mGluRs coupled to the PLC and PLD pathways exist and that mGluR agonists can stimulate PLD through a PKC‐independent mechanism.
Properties of spontaneous depolarizations in circular smooth muscle cells of rabbit urethra
Authors: Hashitani Hikaru , Van Helden Dirk F. , Suzuki Hikaru
Published: July 2012

. Intracellular microelectrode recordings were made from circular smooth muscle of rabbit urethra.

. The smooth muscle of urethra was spontaneously active exhibiting large, regularly occurring depolarizations, termed slow waves (SWs), 1–3 s in duration, up to 40 mV in amplitude and generated every 3–15 s and small irregularly occurring events (or summations there of) termed spontaneous transient depolarizations (STDs) of < 1 s in duration.

. The SWs and STDs were not sensitive to 10−6 m atropine, 10−6 m phentolamine, 10−5 m guanethidine or 10−6 m tetrodotoxin, indicating that they were myogenic in origin.

. Application of 3 × 10−6 m nifedipine or 5 × 10−5 m GdCl3 did not inhibit the generation of SWs or STDs, indicating that activation of L‐type Ca2+ channels and non‐selective cation channels are not essential for their generation. However, the duration of SWs but not STDs was reduced by nifedipine, indicating L‐type Ca2+ channels contribute to the plateau‐like potential of SWs.

. Application of low chloride solution (6.4 mM), niflumic acid (10−5‐10−4 m) or 4,4′‐diisothiocyanostilbene‐2,2′‐disulphonic acid (DIDS, 10−4‐5 × 10−4 m) inhibited the generation of SWs and STDs, suggesting an involvement of chloride channels.

. Application of nominally Ca2+ free solution, 5 × 10−5 m BAPTA‐AM, 10−5 m cyclopiazonic acid, 10−2 m caffeine or 10−3 m procaine inhibited the generation of SWs and STDs, indicating that Ca2+ released from intracellular stores was required for the generation of SWs and STDs.

. Exogenously applied noradrenaline (10−7‐10−5 m) increased the frequency of SWs through stimulation of α‐adrenoceptors which was inhibited by sodium nitroprusside (SNP, 10−4 m). SNP also reduced the frequency of SWs without altering the membrane potential, an effect mimicked by 8‐bromocyclic GMP (10−3 m) indicating that SNP acted by elevating the production of cyclic GMP.

. It is concluded that smooth muscle cells of the rabbit urethra exhibit SWs and STDs which are likely to be induced by stimulation of Ca2+‐activated chloride channels evoked by release of Ca2+ from intracellular stores.
Action of probucol in arteries from normal and hypercholesterolaemic rabbits
Authors: Del Rio M. , Chulia T. , Ruiz E. , Tejerina T.
Published: July 2012

. The effect of probucol on the vascular reactivity of different arteries isolated from rabbits was studied as well as its effects on the development of atherosclerosis in a cholesterol‐fed rabbit model.

. Probucol 10−6‐5 × 10−4 m produced a concentration‐dependent inhibition of the contractile responses induced by KCl (80 mM), the sequence for the IC50 was: mesenteric artery (5th branch, 4.8 ± 2.6 × 10−5 m) > aorta (8.2 ± 2.3 × 10−5 m) > femoral artery (> 5 × 10−4 m). The response to noradrenaline was: mesenteric artery (5th branch, 4.2 ± 1.3 × 10−5 m) > aorta (3.2 ± 3.0 × 10−4 m) > femoral (> 5 × 10−4 m).

. In the aorta, probucol (10−5‐10−4 m) shifted the concentration‐response curves to Ca2+ downward and to the right.

. Probucol at 5 × 10−5 m and 5 × 10−4 m showed a reduction in the 45Ca2+ uptake in resting, non‐stimulated aortic rings as well as the uptake induced by both noradrenaline 10−6 m and KCl 80 mM.

. In experiments in vivo, probucol did not affect lipid profiles; however, drug‐treatment significantly decreased the cholesterol content of aortic tissue and the extent of intimal surface covered with atherosclerotic lesions.

. The vascular reactivity was recovered in femoral arteries from rabbits on the atherogenic diet plus probucol.

. It is concluded that the effect of probucol in vascular smooth muscle can be attributed to an inhibition of Ca2+ entry through both potential‐ and receptor‐operated pathways. Moreover our findings suggest that the effects of probucol on movement of calcium in vascular smooth muscle may play an important role in the mechanism of antiatherogenic properties of this drug.
The site of anti‐arthritic action of the K‐opioid, U‐50,488H, in adjuvant arthritis: importance of local administration
Authors: Wilson Jodie L. , Nayanar Vim , Walker Judith S.
Published: July 2012

. Currently available pharmacological therapies treat arthritis inadequately. We have previously found that the kappa (K)‐opioid, U‐50,488H (trans‐(±)‐3,4‐dichloro‐N‐methyl‐N‐[2‐(1‐pyrrolidinyl) cyclohexyl]‐benzene‐acetamide methane sulphonate), possesses anti‐arthritic effects. In light of the finding that opioid receptors in the periphery are upregulated during inflammation, K‐opioids may represent a novel therapy for arthritis. The primary aim and unique feature of the present study is to investigate whether opioids exert their anti‐arthritic effects in the periphery. Thus, the dose‐effect relationship of a K‐opioid agonist, U‐50,488H was compared after both local and distant administration. Further, we tested whether the anti‐arthritic effects of this drug are stereospecific and receptor‐mediated by use of opioid antagonists.

. Using an adjuvant model of arthritis in male Lewis rats, arthritis was judged by oedema, radiography and histological changes in the contralateral ankle of the hind limb. Treatment with (±)‐U‐50,488H for 3 days during disease onset and 3 days during established disease significantly attenuated arthritis, but the effects of (±)‐U‐50,488H on radiology and histology varied according to treatment time. Administration of (±)‐U‐50,488H during disease onset had a more marked effect on radiography, suggesting that treatment with that drug should be started early to prevent progressive joint destruction. Further, it was found that (±)‐U‐50,488H, administered for 3 days during the disease onset, either by direct subcutaneous injection into the inflamed paw or at a more distant site into the back of the neck, dose‐dependently attenuated arthritic damage as measured by an index which pooled all three variables. More importantly however, (±)‐U‐50,488H was approximately fourfold more potent as an ‘anti‐arthritic’ agent after local compared to distant subcutaneous injection (ED50; local vs distant: 5.8 ± 1.6 vs 19.5 ± 0.8 mg kg−1).

. Equivalent doses of the (−)−enantiomer (20 mg kg−1 day−1) and the racemate (±) of U‐50,488H (40 mg kg−1 day−1), elicited a similar attenuation of arthritic parameters while the (+)‐enantiomer exacerbated arthritis, suggesting that the anti‐arthritic activity lies solely with the (−)−enantiomer.

. Both the peripherally selective antagonist, naloxone methiodide, and the K‐selective antagonist, MR2266 ((−)−5, 9α‐diethyl‐2‐(3‐furylmethyl)‐2′‐hydroxy‐6,7‐benzomorphan), were able to reverse fully the peripheral anti‐arthritic effects of U‐50,488H, indicating that it exerts its effects through peripheral K‐opioid receptors.

. Taken together, these results not only confirm our previous findings that demonstrate anti‐arthritic effects of U‐50,488H but they indicate that the opioid attenuation of experimental arthritis is mediated via peripheral K‐receptors in the arthritic joint. Peripherally acting K‐opioid agonists should lead to new therapies for arthritis.
Effects on K+ currents in rat cerebellar granule neurones of a membrane‐permeable analogue of the calcium chelator BAPTA
Authors: Watkins Christopher S. , Mathie Alistair
Published: July 2012

. Whole cell recordings of voltage‐activated K+ currents were made with the amphotericin B perforated patch technique from cerebellar granule (CG) neurones of 6–8 days rats that had been in culture for 1 to 16 days. By use of appropriate voltage protocols, the effects of the membrane‐permeant form of BAPTA, 1,2‐bis‐(2‐amino‐phenoxy)ethane‐N,N,N′,N′‐tetraacetic acid acetoxymethyl ester (BAPTA‐AM), on the transient A current (IKA), the delayed rectifier current (IKv) and a standing outward current (IKso) were investigated.

. Bath application of 25 μm BAPTA‐AM inhibited both IKv and IKso in cultured neurones, but did not seem to affect IKA. Neither 25 μm BAPTA (free acid) nor 25 μm ethylenediaminetetraacetic acid acetoxymethyl ester (EDTA‐AM) had any significant effect on the magnitude of IKso. Similarly in short‐term (1–2 days) cultured CG neurones IKv, but not IKA, was inhibited by 25 μm BAPTA‐AM.

. BAPTA‐AM (2.5 μm) reduced IKv in short‐term culture CG neurones, with further inhibition being seen when the perfusate was changed to one containing 25 μm BAPTA‐AM.

. Tetraethylammonium ions (TEA) (10 mM) reversibly inhibited IKv in these cells with a similar rate of block of IKv to that induced by 25 μm BAPTA‐AM.

. The degree of inhibition of IKv by 25 μm BAPTA‐AM was both time‐ and voltage‐dependent, in contrast to the inhibition of this current by TEA.

. These data indicate that BAPTA‐AM reduces K+ currents in cerebellar granule neurones and that this inhibition cannot be explained in terms of intracellular Ca2+ chelation, but is a direct effect on the underlying channels.
Direct chronotropic effects of atrial and C‐type natriuretic peptides in anaesthetized dogs
Authors: Beaulieu Pierre , Cardinal René , De Léan André , Lambert Chantal
Published: July 2012

. The chronotropic effects of atrial natriuretic peptide (ANP) and C‐type natriuretic peptide (CNP) were investigated using injections (50 μg in 1 ml of Tyrode solution as bolus over 1 min) directly into the sinus node artery of 21 anaesthetized and vagotomized dogs which had been pretreated with a β‐adrenoceptor antagonist. The injections were also repeated following: (a) α‐adrenoceptor antagonism (prazosin) and muscarinic receptor antagonism (atropine); (b) inhibition of prostaglandin synthesis (indomethacin); (c) angiotensin II AT1 receptor antagonism (losartan); (d) histamine H1 (mepyramine) and H2 (cimetidine) receptor antagonism.

. The results obtained indicate that ANP had no significant effect on the basal sinus rate, whereas CNP produced a slight but significant increase of 12 ± 2 beats min−1. The effect of CNP was long‐lasting (return to pre‐injection levels after maximum effect in 17 ± 3 min) and was not influenced by the various antagonists mentioned above.

. During in vitro experiments on spontaneously beating right atria isolated from 6 dogs, the injection of CNP (50 μg in 1 ml of Tyrode solution) into the sinus node artery produced an increase in atrial rate of 14 ± 1 beats min−1.

. The results of this work indicate that CNP exerts a significant and prolonged positive chronotropic effect both in vivo and in vitro. Other studies are required to elucidate the mechanism of action of CNP on the heart conduction system, to ascertain the presence of natriuretic peptide receptor B in the region of the sinoatrial node and to determine the role of CNP in the control of heart rate.