Biomedical subjects

W M Zhang

Publications and source records attributed to W M Zhang.

At least 37 records · Page 2Linked to original sources

PubMed1999

Excitonic couplings and electronic coherence in bridged naphthalene dimers.

The electronic excitations of naphthalene and a family of bridged naphthalene dimers are calculated and analyzed by using the Collective Electronic Oscillator method combined with the oblique Lanczos algorithm. All experimentally observed trends in absorption profiles and radiative lifetimes are reproduced. Each electronic excitation is linked to the corresponding real-space transition density matrix, which represents the motions of electrons and holes created in the molecule by photon absorption. Two-dimensional plots of these matrices help visualize the degree of exciton localization and explain the dependence of the electronic interaction between chromophores on their separation.

Journal Article↗

PubMed1999

Cross-talk between cardiac kappa-opioid and beta-adrenergic receptors in developing hypertensive rats.

The kappa-opioid receptor exerts a negative modulatory action on the beta-adrenoceptor and the action is blunted in adult spontaneously hypertensive rats (SHR). In order to determine whether the blunted negative modulation of the beta-adrenoceptor by the kappa-opioid receptor contributes to the development of hypertension, the electrically induced intracellular calcium ([Ca2+]i) transient was measured in single ventricular myocytes of SHR at 4, 6, 8 and 13-week-old and the age-matched Wistar Kyoto (WKY) rats. The electrically induced [Ca2+]i transients were augmented by norepinephrine (NE), a beta-adrenoceptor agonist, over four-fold in WKY rats of all ages studied and in SHR of 4 and 6 weeks of age. The enhancing effect of NE in 8- and 13-week-old SHR was, however, only approximately three-fold, significantly lower than the corresponding values in age-matched WKY rats. Similarly, the electrically induced [Ca2+]i transients were also augmented by forskolin, an activator of adenylate cyclase, by approximately two-fold in WKY rats of all ages and SHR aged 4 and 6 weeks. In SHR aged 8 and 13 weeks, the effect of forskolin was only 1.5-fold, significantly lower than the two-fold increase in the corresponding WKY rats. The enhancing effects of NE and forskolin were attenuated by U50,488H, a selective kappa-opioid agonist, by approximately 50 and 25%, respectively, in both types of rats of all ages studied, with the exception of 13-week-old rats. In rats of this age group, the attenuations by U50,488H on the enhancing effects of NE and forskolin were 17 and 9% in SHR, respectively, significantly less than the corresponding 54 and 29% in WKY. The fact that attenuation of U50,488H on the enhancing effects of NE and forskolin only occurs in 13-week-old SHR when hypertension has been fully developed indicates that the attenuated inhibitory modulation of kappa-opioid receptor stimulation does not contribute to the initiation of hypertension. Interestingly, the enhancing effects of NE and forskolin on the electrically induced [Ca2+]i transient was attenuated in SHR aged from 8 weeks when the blood pressure was rapidly increasing. The different time courses of altered responses to U50,488H, and NE and forskolin suggest that the attenuated negative modulation of kappa-receptor stimulation on the beta-adrenergic receptor is not due to the signal transduction pathway activated by beta-adrenergic stimulation. In 13-week-old SHR with the arterial blood pressure restored to normal by pharmacological manipulations, the blunted responses to NE, U50,488H and forskolin still occurred, indicating that the altered responses to activation of beta-adrenergic and kappa-opioid receptors and adenylate cyclase are not secondary to hypertension.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1999

Effects of U50488 and bremazocine on [Ca2+]i and cAMP in naive and tolerant rat ventricular myocytes: evidence of kappa opioid receptor multiplicity in the heart.

To explore the existence of multiplicity of kappa receptor in the heart, two series of experiments were performed. In the first we studied the antagonistic actions of nor-BNI, a selective kappa 1 antagonist, and quadazocine, a preferential kappa 2 antagonist, against the effects of U50488, a selective kappa 1 agonist, and bremazocine, a universal agonist preferentially binding to kappa 2 receptor, on the electrically stimulated [Ca2+]i transient and forskolin-stimulated cAMP accumulation in the rat ventricular myocyte. In the second series of experiments, we determined and compared the effects of above two kappa receptor agonists in the ventricular myocytes made insensitive to kappa 1 and kappa 2 agonists by prior exposure to the respective agonists. At the concentration range of 3 x 10(-6)-3 x 10(-5) M, both U50488 and bremazocine dose-dependently inhibited the [Ca2+]i transient induced by electrical stimulation. The inhibitory effects of U50488 and bremazocine were antagonized by nor-BNI and quadazocine. The antagonistic actions of nor-BNI were significantly greater against the effects of U50488, but smaller against the effects of bremazocine than those of quadazocine. At 1 x 10(-6)-5 x 10(-5) M, both U50488 and bremazocine dose-dependently and significantly inhibited the forskolin-induced cAMP accumulation. The inhibitory effect of 30 microM U50488 on cAMP accumulation was significantly attenuated by 5 microM nor-BNI, but not by quadazocine at the same concentration; whereas the effect of 30 microM bremazocine was significantly blocked by 5 microM quadazocine, but not by nor-BNI at the same concentration. The inhibitory effect of 30 microM U50488 on electrically stimulated [Ca2+]i was abolished by preincubation of myocytes with 10(-6) M U50488 for 24 h, but not with 10(-6) M bremazocine for h; whereas the inhibitory effect of 30 microM bremazocine on electrically stimulated [Ca2+]i transient was significantly attenuated after incubation of the myocyte with 10(-6) M bremazocine for 24 h, but not with 10(-6) M U50488 for 24 h. The observations indicate the existence of kappa receptor subtypes in the rat heart.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1999

Prostate-specific antigen.

Prostate specific antigen (PSA) is serine protease produced at high concentrations by normal and malignant prostatic epithelium. It is mainly secreted into seminal fluid, where it digests the gel forming after ejaculation. Only minor amounts of PSA leak out into circulation from the normal prostate, but the release of PSA is increased in prostatic disease. Thus PSA is a sensitive serum marker for prostate cancer but its specificity is limited by a high frequency of falsely elevated values in men with benign prostatic hyperplasia (BPH). Approximately two-thirds of all elevated values (>4 microg/l) in men over 50 years of age are due to BPH. In serum, most of the PSA immunoreactivity consists of a complex between PSA and alpha1-antichymotrypsin (PSA-ACT) whereas approximately 5-40% are free. The proportion of PSA-ACT is larger and the free fraction is smaller in prostate cancer than in benign prostatic hyperplasia (BPH). Determination of the proportion of free PSA has become widely used to improve the cancer specificity of PSA especially in men with PSA values in the 'grey zone' (4-10 microg/l). PSA also occurs in complexes with other protease inhibitors and determination of these and other markers may further improve the diagnostic accuracy for prostate cancer. Interpretation of the results for many different markers is complicated, but this can be simplified by using statistical methods. The diagnostic accuracy can be further improved by using logistic regression or neural networks to estimate the combined impact of marker results and other findings like digital rectal examination (DRE), transrectal ultrasound (TRUS) and heredity.

Humans↗

PubMed1999

Fractures of the patella in children.

Fractures of the patella are relatively rare injuries for children. Fourteen patients with patellar fractures were reviewed. There were 12 boys and two girls with the age ranging between 9 and 15 years and an average of 11.4 years. Sleeve fractures were the most common type of patellar fractures observed (eight cases), followed by transverse fractures (four cases) and comminuted fractures (two cases). All the fractures were treated with open reduction and followed up for 2 to 20 years. Overall results were good in 13 patients, and flexion limitation of the knee was seen in one. Fractures of the patella in children are characterised by sleeve fractures. The prognosis of the patients treated with open reduction is generally good.

Adolescent↗

PubMed1999

Heat shock induction of a 65 kDa ATP-binding proteinase in rat C6 glioma cells.

The 45, 55, 65 and 100 kDa ATP-binding proteinases (ATP-BPases) of the heat-shocked (44 degrees C for 30 min, recovery for 12 h) rat C6 glioma cells were purified by DEAE-ionexchange and ATP-affinity chromatography. Their molecular masses, isoelectric points (pI), pH-optima and other properties were analyzed by native proteinase gels. It was shown that the 65 kDa ATP-BPase is specifically induced by heat shock and not detectable in control cells. Its N-terminal 1-9 amino acid sequence was determined by Edman degradation, but no homologies to other proteins in the protein data bases were found. 30 and 31 kDa proteinases can be cleaved from the 45, 55 and 65 kDa proteinases to which they are linked. A possible relationship of the heat-induced 65 kDa ATP-BPase with the ATP-dependent proteinases (ATP-DPases) in prokaryotes and eukaryotes is discussed.

Adenosine Triphosphate↗

PubMed1999

Reactivity of 77 antibodies to prostate-specific antigen with isoenzymes and complexes of prostate-specific antigen.

Seventy-seven antibodies submitted to the ISOBM TD-3 PSA Workshop (TD-3.1 and TD-3.2) were characterized by measuring their reactivity with isoenzymes of free prostate-specific antigen (PSA), PSA complexed to alpha1-antichymotrypsin (PSA-ACT) and alpha1-proteinase inhibitor (PSA-API). Antibodies were classified into 15 distinct groups according to their reaction profiles with the various isoenzymes. Some antibodies recognizing both free and complexed PSA were inaccurate in measuring total PSA. Eight of the 9 free PSA-specific antibodies cross-reacted more with PSA-API than with PSA-ACT, while 1 antibody reacted less with PSA-API than PSA-ACT. From the panel of antibodies 39 reacted with both free and complexed PSA and were classified as total PSA antibodies.

Antibodies, Monoclonal↗

PubMed1999

Reactivity of anti-PSA monoclonal antibodies with recombinant human kallikrein-2.

Seventy-nine monoclonal antibodies submitted to the ISOBM TD-3 PSA Workshop were tested for their reactivity with recombinant human kallikrein-2 (rhK2). A sandwich immunofluorometric assay using polyclonal anti-prostate-specific antigen (PSA) antiserum-coated plates was used to capture rhK2 and subsequently the test antibody. The response of each test antibody was compared with 3 reference antibodies (H50, H117 and 5E4) known to react with hK2. Nine antibodies from the workshop panel failed to react with purified PSA and rhK2 in this assay and were subsequently excluded. From the remaining panel of antibodies, 11/70 showed strong reactivity with rhK2, 9/70 showed weak reactivity with rhK2, while 50/70 antibodies did not react with rhK2 in this assay format. All antibodies binding to rhK2 recognized both free and complexed PSA.

Antibodies, Monoclonal↗

PubMed1999

Measurement of the complex between prostate-specific antigen and alpha1-protease inhibitor in serum.

BACKGROUND: Prostate-specific antigen (PSA) occurs in serum both free and in complex with protease inhibitors. The complex with alpha1-antichymotrypsin (ACT) is the major form in serum, and the proportion of PSA-ACT is higher in prostate cancer (PCa) than in benign prostatic hyperplasia (BPH). PSA also forms a complex with alpha1-protease inhibitor (API) in vitro, and the PSA-ACT complex has been detected in serum from patients with prostate cancer. The aim of the present study was to develop a quantitative method for the determination of PSA-API and to determine the serum concentrations in patients with PCa and BPH. METHODS: The assay for PSA-API utilizes a monoclonal antibody to PSA as capture and a polyclonal antibody to API labeled with a Eu-chelate as a tracer. For calibrators, PSA-API formed in vitro was used. Serum samples were obtained before treatment from 82 patients with PCa, from 66 patients with BPH, and from 22 healthy females. RESULTS: The concentrations of PSA-API are proportional to the concentrations of total PSA. PSA-API comprises 1.0-7.9% (median, 2.4%) of total immunoreactive PSA in PCa and 1.3-12.2% (median, 3.6%) in BPH patients with serum PSA concentrations >4 microgram/L. In patients with 4-20 microgram/L total PSA, the proportion of PSA-API serum is significantly higher in BPH (median, 4.1%) than in PCa (median, 3. 2%; P = 0.02). CONCLUSIONS: The proportion of PSA-API in serum is lower in patients with PCa than in those with BPH. These results suggest that PSA-API is a potential adjunct to total and free PSA in the diagnosis of prostate cancer.

Electrophoresis, Polyacrylamide Gel↗

PubMed1998

Phospholipase C inhibitors attenuate arrhythmias induced by kappa-receptor stimulation in the isolated rat heart.

To determine whether the phospholipase C (PLC)/inositol 1,4,5 trisphosphate (IP3)/Ca2+ pathway mediates cardiac arrhythmias induced by kappa-opioid receptor stimulation, the effects of U50,488H, a selective kappa-opioid receptor agonist, on cardiac rhythm in a isolated perfused rat heart, intracellular calcium ([Ca2+]i) in a single ventricular myocyte and IP3 production in myocytes were studied in the presence and absence of PLC inhibitors. U50,488H, the effects of which had been shown to be abolished by a selective kappa-receptor antagonist, nor-binaltorphimine, induced arrhythmias dose-dependently and increased both [Ca2+]i and IP3-production in the heart. More importantly, the effects of U50,488H were blocked by PLC inhibitors, neomycin and streptomycin. To further confirm the selectivity of action of the PLC inhibitor, the effects of another PLC inhibitor U73122 and its inactive structural analog, U73343, on cardiac rhythm in the isolated perfused rat heart were compared. The former did, while the latter did not, block the arrhythmogenic effect of U50,488H. We also determined whether the effects of kappa-receptor stimulation involves a pertussis toxin (PTX)-sensitive G-protein. We found that pretreatment with PTX at 4 microg/l for 10 min, a treatment shown to affect PTX sensitive G-protein-mediated functions, attenuated significantly the U50,488H-induced arrhythmias. The present study provides evidence that kappa-receptor stimulation-induced cardiac arrhythmias involves, at least partly, the PLC/IP3/Ca2+ pathway as well as a PTX sensitive G-protein.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1998

Effects of kappa-opioid receptor stimulation in the heart and the involvement of protein kinase C.

1. The role of protein kinase C (PKC) in mediating the action of kappa-receptor stimulation on intracellular Ca2+ and cyclic AMP production was determined by studying the effects of trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulphonate (U50,488H), a selective kappa-receptor agonist, and phorbol 12-myristate 13-acetate (PMA), a PKC agonist, on the electrically-induced [Ca2+]i transient and forskolin-stimulated cyclic AMP accumulation in the presence and absence of a PKC antagonist, staurosporine or chelerythrine, in the single rat ventricular myocyte. 2. U50,488H at 2.5-40 microM decreased both the electrically-induced [Ca2+]i transient and forskolin-stimulated cyclic AMP accumulation dose-dependently, effects which PMA mimicked. The effects of the kappa-agonist, that were blocked by a selective kappa-antagonist, nor-binaltorphimine, were significantly antagonized by the PKC antagonists, staurosporine and/or chelerythrine. The results indicate that PKC mediates the actions of kappa-receptor stimulation. 3. To determine whether the action of PKC was at the sarcoplasmic reticulum (SR) or not, the [Ca2+]i transient induced by caffeine, that depletes the SR of Ca2+, was used as an indicator of Ca2+ content in the SR. The caffeine-induced [Ca2+]i transient was significantly reduced by U50,488H at 20 microM. This effect of U50,488H on caffeine-induced [Ca2+]i transient was significantly attenuated by 1 microM chelerythrine, indicating that the action of PKC involves mobilization of Ca2+ from the SR. When the increase in IP3 production in response to K-receptor stimulation with U50,488H in the ventricular myocyte was determined, the effect of U50,488H was the same in the presence and absence of staurosporine, suggesting that the effect of PKC activation subsequent to kappa-receptor stimulation does not involve IP3. The observations suggest that PKC may act directly at the SR. 4. In conclusion, the present study has provided evidence for the first time that PKC may be involved in the action of kappa-receptor stimulation on Ca2+ in the SR and cyclic AMP production, both of which play an essential role in Ca2+ homeostasis in the heart.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1998

The clinical importance of free prostate-specific antigen (PSA).

The proportion of free prostate-specific antigen (PSA) in serum relative to total PSA (F/T) is lower in patients with prostate cancer than in those with elevated levels of PSA due to benign prostatic disease. When applied to early diagnosis and screening for prostate cancer, the proportion of free PSA can be used to reduce the number of false-positive results by 20-40%. The utility of F/T is better in men with a small prostate volume, i.e. in relatively young men, who are most likely to benefit from early diagnosis and treatment of prostate cancer. The concentrations of PSA and especially free PSA are affected by considerable intra-individual variation and sample stability. Assay standardization is variable and it is therefore important to establish reference values for the methods used. Better control of these factors is likely to improve the diagnostic accuracy. The utility of determining free PSA can be improved by evaluating the combined impact of free and total PSA by logistic regression analysis or neural networks.

Journal Article↗

PubMed1998

Neutron yields from 435 MeV/nucleon Nb stopping in Nb and 272 MeV/nucleon Nb stopping in Nb and Al.

Neutron fluences were measured from 435 MeV/nucleon Nb ions stopping in a Nb target and 272 MeV/nucleon Nb ions stopping in targets of Nb and Al for neutrons above 20 MeV and at laboratory angles between 3 degrees and 80 degrees. The resultant spectra were integrated over angles to produce neutron energy distributions and over energy to produce neutron angular distributions. The total neutron yields for each system were obtained by integrating over the angular distributions. The angular distributions from all three systems are peaked forward, and the energy distributions from all three systems show an appreciable yield of neutrons with velocities greater than the beam velocity. Comparison of the total neutron yields from the two Nb + Nb systems suggests that the average neutron multiplicity decreases with decreasing projectile energy. Comparison of the total yields from the two 272 MeV/nucleon systems suggests that the total yields show the same dependence on projectile and target mass number as do total inclusive neutron cross sections. The data are compared with Boltzmann-Uehling-Uhlenbeck model calculations.

Aluminum↗

PubMed1998

Suppression of cAMP by phosphoinositol/Ca2+ pathway in the cardiac kappa-opioid receptor.

To determine whether the phosphoinositol/Ca2+ pathway interacts with the adenylate cyclase/adenosine 3',5'-cyclic monophosphate (cAMP) pathway in the cardiac kappa-receptor, the effects of U-50488, a specific kappa-receptor agonist, on the intracellular Ca2+ concentration ([Ca2+]i) and forskolin-induced accumulation of cAMP in rat ventricular myocytes were determined after interference of the phosphoinositol/Ca2+ pathway. U-50488 suppressed the forskolin-induced accumulation of cAMP and elevated [Ca2+]i, which were blocked by norbinaltorphimine, a specific kappa-receptor antagonist, and pertussis toxin. The effects of U-50488 were qualitatively similar to those of A-23187, a Ca2+ ionophore, but opposite to those of 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (AM), a [Ca2+]i chelator. Abolition of U-50488-induced elevation of [Ca2+]i by BAPTA-AM also abolished the effect of U-50488 on forskolin-induced accumulation of cAMP. Inhibition of the phospholipase C by specific inhibitors, U-73122 and neomycin, abolished the effects of U-50488 on both [Ca2+]i and forskolin-induced accumulation of cAMP. The results showed for the first time that kappa-receptor stimulation may suppress cAMP accumulation via activation of the phosphoinositol/Ca2+ pathway in the rat heart.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1998

Characterization and immunological determination of the complex between prostate-specific antigen and alpha2-macroglobulin.

Prostate-specific antigen (PSA) rapidly forms a complex with alpha2-macroglobulin (A2M) in vitro; however, PSA complexed with A2M (PSA-A2M) is not detected by conventional immunoassays for PSA because it is encapsulated by the A2M. In this study, we show that denaturation of PSA-A2M at high pH renders PSA immunoreactive. Part of the complexed PSA is released in free form and part remains bound to denatured A2M. These forms can be measured by a conventional immunoassay for PSA. This finding enabled us to design a dissociation assay for the detection of PSA-A2M, which was based on the removal of immunoreactive PSA in serum by immunoadsorption, denaturation of PSA-A2M at high pH, and measurement of the released PSA immunoreactivity by a conventional PSA immunoassay. This PSA-A2M assay was calibrated with PSA-A2M formed in vitro. The detection limit of the assay was 0.14 microg/L. Inter- and intraassay coefficients variation were 4-9% and 8-14%, respectively. When purified PSA was incubated with A2M, the loss of PSA immunoreactivity was highly correlated with the PSA-A2M formed, as measured by the dissociation assay for PSA-A2M (r = 0.99; P <0.0001). The concentration of PSA-A2M in serum correlated with that of total PSA both in prostate cancer (PCa) and benign prostatic hyperplasia (BPH); however, the ratio of PSA-A2M in relation to total PSA was significantly higher in BPH than in PCa (P <0.0003). ROC curve analysis suggested that measurement of the ratio of PSA-A2M to total PSA in serum improves the diagnostic accuracy for PCa compared with assays for total PSA only.

Aged↗

PubMed1997

Prostate-specific antigen forms a complex with and cleaves alpha 1-protease inhibitor in vitro.

BACKGROUND: Complexes between prostate-specific antigen (PSA) and alpha 1-protease inhibitor (API) occur in serum and they are of potential interest in the diagnosis of prostate cancer. Pure PSA-API complexes are needed for development of specific assays, but complex formation has not earlier been achieved in vitro. METHODS: PSA was incubated with an excess of API at 37 degrees C. Complexes formed were quantitated by an immunofluorometric assay using antibodies to PSA and API. The products were further characterized by SDS-PAGE, immunoblotting and amino-acid sequencing. PSA-API was purified by gel filtration and immunoaffinity chromatography. RESULTS: PSA formed an SDS-stable 80-kDa one-to-one complex with API. The rate of formation of PSA-API was slow compared to that of PSA-alpha 2-macroglobulin (A2M) or PSA-alpha 1-antichymotrypsin (ACT), and only about 15% of PSA complexed with a 5-fold molar excess of API at 37 degrees C in 7 days. A major part of API was cleaved between 358-Met and 359-Ser, causing loss of inhibitory activity. PSA-API formed in vitro was purified by gel filtration and immunoaffinity chromatography with anti-PSA antibody. After incubation for 7 days at 37 degrees C, 30-40% of the complex had dissociated causing release of active PSA and proteolytically cleaved inactive API. The dissociation was accelerated in the presence of serum, and released PSA complexed with A2M and ACT. CONCLUSIONS: PSA forms a complex with API in vitro, but the reaction is slow and part of the API is cleaved. Complex formation is reversible and released PSA is enzymatically active, whereas API is inactivated. Purified PSA-API will facilitate development of quantitative immunoassays for this complex.

Chromatography, Affinity↗

PubMed1997

High carbachol increases the electrically induced [Ca2+]i transient in the single isolated ventricular myocyte of rats.

In order to investigate the mechanisms responsible for the inotropic effects of muscarinic acetylcholine receptor stimulation by high concentrations of muscarinic receptor agonists, we studied the effects of carbachol at 30-300 microM on the electrically induced [Ca2+]i transient of rat isolated ventricular myocytes. Carbachol at this dose range increased the amplitude and duration of the electrically induced [Ca2+]i transient time and dose dependently. It also increased the resting fluorescence ratio and time to 80% decline of amplitude from the peak. At 100-300 microM the increase in [Ca2+]i transient was followed by a cluster of Ca2+ oscillations in 50-83% of the cells studied. The effects were blocked by atropine, but not pertussis toxin. Depletion of Ca2+ from sarcoplasmic reticulum by ryanodine, which itself reduced the amplitude of the [Ca2+]i transient and increase resting fluorescence, abolished the effect of carbachol on the [Ca2+]i transient without affecting its effect on resting fluorescence ratio. The caffeine-induced [Ca2+]i transient was unaffected by prior addition of carbachol in a Ca2+ free and low Na+ solution. Inhibition of Ca2+ by the L-type Ca2+ channel blocker, verapamil, which itself reduced the amplitude of the [Ca2+]i transient without affecting the resting fluorescence ratio, attenuated the augmentation of the amplitude of the [Ca2+]i transient elicited by carbachol. Ni2+, a non-specific Ca2+ channel blocker and an inhibitor of Na(+)-Ca2+ exchange, abolished the effects of carbachol on both [Ca2+]i transient and resting fluorescence ratio. Low external Na+, which increased the resting fluorescence ratio due to its inhibitory effect on Na(+)-Ca2+ exchange, also abolished the effects of carbachol. The results indicate that the inotropic effect of muscarinic acetylcholine receptor stimulation by high concentrations of a muscarinic receptor agonist may be due to an increase in the electrically induced [Ca2+]i transient in ventricular myocytes via a process which is not pertussis toxin sensitive. The increase in the electrically induced [Ca2+]i transient may result from increases in Na2(+)-Ca2+ exchange and influx of Ca2+ via voltage-gated Ca2+ channels, and mobilization of Ca2+ from the intracellular store. The mobilization of Ca2+ from the intracellular store is a secondary event. The study has provided for the first time that muscarinic acetylcholine receptor stimulation by high concentrations of carbachol increases Ca2+ influx via the Ca2+ channel and mobilization of Ca2+ from its intracellular store. The study has also demonstrated for the first time the occurrence of Ca2+ oscillations induced by high concentrations of carbachol.

Animals↗

PubMed1997

Inhibition of [3H]-U69593 binding and the cardiac effects of U50, 488H by calcium channel blockers in the rat heart.

1. The calcium channel blockers (CCBs), nifedipine, nicardipine, diltiazem and verapamil, were used to displace the binding of [3H]-U69593 ((5a, 7a,8b)-(+)-N-methyl-N-(7-[1-pyrrolidinyl]-1-oxaspiro[4,5] dec-8-yl)-benzeneacetamide), a specific kappa-opioid agonist, in the rat cardiac sarcolemma. The CCBs competed with the binding of [3H]-U69593 (4 nM) in a dose-dependent manner. The displacing potency of verapamil was 55 times greater than that of nifedipine. 2. The effects of two CCBs, verapamil and nifedipine, on the arrhythmogenic action of kappa-receptor stimulation by a specific kappa-receptor agonist, U50,488H (trans-(+/-(-3),4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeacetamide methanesulphonate), were also studied in the rat isolated perfused heart. U50,488H 80-800 nmol dose-dependently induced arrhythmias, which were completely abolished by a selective kappa-receptor antagonist, nor-BNI (nor-binaltorphimine, 17,17'-(dicyclopropylmethyl)-6,6',7,7'-6,6'-imino-7,7'-binorphinan -3,4',14, 14'-tetrol), at 100 nmol. The arrhythmogenic effect was also attenuated by both verapamil and nifedipine in a dose-dependent manner. The ED50 values for verapamil and nifedipine were 2.75 and 63.7 nmol, respectively. The antiarrhythmic potencies of these two CCBs were correlated to their displacing potencies and inversely related to their well known potencies in inhibiting transmembrane Ca2+ influx in the cardiac muscle. 3. Measurement of [Ca2+]i in the absence of free extracellular Ca2+ by a spectrofluorometric method, with fura-2 as Ca2+ indicator, showed that U50,488H 5 x 10(-5) M slowly increased [Ca2+]i in single ventricular myocytes and this effect was abolished by pretreatment with nor-BNI (5 microM), or ryanodine (5 microM). Verapamil 1 and 10 microM abolished the effect of U50,488H in 37.5% (3 out of 8) and 100% (12 out of 12) of the cells studied, respectively. On the other hand, nifedipine 10 and 100 microM had no effect at all. Neither verapamil nor nifedipine exerted any significant effect on the caffeine-induced Ca2+ transient. 4. The observations suggest that CCBs may inhibit the actions of kappa-receptor stimulation at the level of the kappa-receptor.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗