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Q Y Liu

Publications and source records attributed to Q Y Liu.

At least 73 records · Page 4Linked to original sources
PubMed1994

Changes in alpha 1-adrenoceptor coupling to Ca2+ channels during development in rat heart.

It has been reported in the literature that alpha 1-adrenoceptor activation in adult rat heart does not cause an increase in Ca2+ current but involves a decrease in I(t). This may explain in part the positive inotropic effect of alpha 1-adrenoceptor activation. In this study, the effect of phenylephrine, an alpha-adrenergic agonist, on L-type Ca2+ channel current was compared in young and neonatal rat myocytes. In the presence of propranolol, phenylephrine increased the Ca2+ current (reversed by prazosin) in neonatal but not in young rat myocytes suggesting that the coupling of the alpha 1-adrenoceptor to Ca2+ channels may switch during development.

Aging↗
PubMed1994

Mechanisms underlying the modulation of arrhythmogenic events by components of ischemia in guinea pig cardiac myocytes.

The effects of some components of ischemia on the oscillatory (Vos) and nonoscillatory (V(ex)) potentials and respective currents (Ios and Iex), as well as their mechanisms, were studied in guinea pig isolated ventricular myocytes by means of a single-microelectrode, discontinuous voltage clamp method. Repetitive activations induced not only Vos and Ios, but also V(ex) and Iex. A small decrease in resting potential caused an immediate increase in Vos followed by a gradual increase due to the longer action potential. Immediate and gradual increases in Ios also occurred during voltage clamp steps. A small depolarization increased Vos and V(ex), and facilitated the induction of spontaneous discharge by fast drive. At Vh where INa is inactivated, depolarizing steps induced larger Ios and Iex, indicating the importance of the Na-independent Ca loading. High [K]o decreased the resting potential, but also Vos, V(ex), Ios, Iex, and ICa. In high [K]o, depolarization still increased Vos and V(ex). Norepinephrine (NE) enhanced Vos and V(ex), and also Ios and Iex, during voltage clamp steps. High [K]o antagonized NE effects, and NE those of high [K]o. In conclusion, on depolarization, Vos and Ios immediately increase through a voltage-dependent mechanism; and then Vos and Ios gradually increase, apparently through an increased Ca load related to the longer action potentials and the Na-Ca exchange. The depolarization induced by V(ex) may contribute to increase Vos size. Vos and V(ex) are similarly influenced by different procedures that modify Ca load. The arrhythmogenic events are enhanced by the simultaneous presence of depolarization, faster rate, or NE. Instead, high [K]o decreases Vos and V(ex) by decreasing ICa and opposes the effects of NE. The voltage clamp results show that potentiation and antagonism between different components of ischemia are due primarily to changes in Ca loading and not to changes in action potential configuration.

Action Potentials↗
PubMed1994

Vascular effects of 17 beta-estradiol in male Sprague-Dawley rats.

Bolus intravenous injections of 100 micrograms/kg 17 beta-estradiol significantly decreased the pressor responses to norepinephrine (NE; 0.3 microgram/kg) at the fourth, fifth, and sixth hour in anesthetized male Sprague-Dawley rats. At doses of 10(-6) to 3 x 10(-5) M, 17 beta-estradiol relaxed the sustained phase of contraction in male Sprague-Dawley rat tail artery helical strips precontracted in vitro by [Arg8]vasopressin (AVP), KCl, or NE. The effect was dose dependent. At doses of 3 x 10(-6) to 3 x 10(-5) M, it also decreased the initial phase of tension generation and extracellular Ca(2+)-dependent vasoconstriction induced by NE, AVP, or KCl in a dose-dependent manner in male Sprague-Dawley rat tail artery helical strips. 17 beta-Estradiol (2 x 10(-8) to 2 x 10(-6) M) decreased the voltage-dependent inward Ca2+ current and the intracellular free Ca2+ concentration ([Ca2+]i) increment induced by 15 mM KCl in a dose-dependent manner (3.6 x 10(-8) to 3.6 x 10(-6) M) in vascular smooth muscle cells (VSMC) isolated from male Sprague-Dawley rat tail arteries. We suggest that, at pharmacological doses, estrogen has a direct vasodilating effect on the rat tail artery that is mediated by its inhibitory effect on Ca2+ influx through voltage-dependent Ca2+ channels. The inhibitory effect of estrogen on the pressor responses to NE or AVP may be correlated with its modulation of VSMC [Ca2+]i through its actions on membrane Ca2+ channels.

Animals↗
PubMed1994

Isolation of a gametophyte-specific cDNA encoding a lipoxygenase from the red alga Porphyra purpurea.

A cDNA clone encoding a lipoxygenase was obtained from a subtracted cDNA library specific for the gametophyte of Porphyra purpurea. The amino acid sequence of the P. purpurea lipoxygenase is most similar to the sequences of animals and plants in the iron-binding, catalytic region located in the C-terminal half of the enzymes. Northern hybridization confirmed that the gene represented by this cDNA is expressed only in the gametophyte.

Amino Acid Sequence↗
PubMed1994

gamma-Aminobutyric acid type A receptor antagonists picrotoxin and bicuculline alter acetylcholine channel kinetics in cultured embryonic rat skeletal muscle.

The effects of the classical gamma-aminobutyric acid type A receptor antagonists picrotoxin and bicuculline on nicotinic acetylcholine receptors in cultured embryonic rat skeletal muscle were examined with whole-cell and cell-attached single-channel recording methods. Up to 600 microM picrotoxin had little or no effect on the amplitude of the whole-cell current, whereas bicuculline dose-dependently blocked it, with an IC50 value of 101.2 +/- 8.9 microM. Bicuculline reduced the maximum inducible acetylcholine current without changing the Kd value, suggesting that bicuculline uncompetitively blocked the binding of acetylcholine to its receptor. The elementary nicotinic acetylcholine receptor currents recorded in the cell-attached single-channel recording configuration exhibited properties typical of those recorded in embryonic muscle (approximately 36 pS and approximately 6 msec). Picrotoxin dramatically transformed individual channel openings into briefly interrupted bursts, so that the number of openings increased while the mean open time markedly decreased. Bicuculline decreased mean open time to a lesser but statistically significant degree. The dominant component of the closed time histogram in control recordings occurred at 17 msec, whereas that recorded with picrotoxin occurred at 0.5 msec. Bicuculline prolonged the closed time, with a dominant closed time component at 52 msec. Elementary conductance was not altered by either agent. In conclusion, we found that the gamma-aminobutyric acid type A channel antagonists picrotoxin and bicuculline were also blockers of embryonic nicotinic acetylcholine receptor channels in cultured rat muscle.

Animals↗
PubMed1994

Calpastatin gene in human testis.

Antibodies present in a serum obtained from an infertile woman interacted with a 17.5 kD glycoprotein (BS-17 component) extracted from human sperm by Western blot. Polyclonal antibodies were raised against the BS-17 component and used to identify positive staining clones from a human testis lambda gt11 expression library. The cDNA encoding the BS-17 component was isolated and its nucleotide sequence determined. The BS-17 cDNA contained 758 nucleotides with an open reading frame of 558 nucleotides encoding a polypeptide consisting of 186 amino acids. The BS-17 cDNA showed 99.7% homology in 758 nucleotides overlap with the 3' terminus of the gene coding calpastatin and 99.5% identity in 186 amino acid overlap with the carboxyl terminus of calpastatin. The BS-17 component of human sperm corresponds to the carboxyl terminus of calpastatin. This conclusion is supported by the finding that the polyclonal antibodies also interacted with a 84 kD protein corresponding to the M(r) of calpastatin.

Amino Acid Sequence↗
PubMed1994

The L-type calcium channel current is increased by alpha-1 adrenoceptor activation in neonatal rat ventricular cells.

The activation of alpha-1 adrenoceptors in adult rat ventricular cells results in the reduction of the transient outward K+ current, but does not affect Ca++ currents. In this study, using neonatal rat ventricular cells, the alpha-1 adrenergic receptor agonist phenylephrine increased the long-lasting (L-type) Ca++ channel current (dihydropyridine-sensitive) and the increase was concentration-dependent. Phenylephrine did not, however, modulate the transient-type (T-type) Ca++ channel current. The alpha-1 effect of phenylephrine was reversed or abolished by prazosin, an alpha-1 antagonist. The alpha-2 agonist clonidine had no effect on the L-type current. Yohimbine, an alpha-2 antagonist, and propranolol, a beta antagonist, did not inhibit the effect of phenylephrine on L-type current. The effect of phenylephrine was abolished by pretreatment with WB4101, an alpha-1A antagonist, but not by chloroethylclonidine, an alpha-1B antagonist. In addition, norepinephrine also increased the L-type current in the presence of propranolol and this effect was reversed by washout. These observations suggest that phenylephrine increased the L-type Ca++ channel current specifically through the activation of alpha-1A adrenergic receptors in neonatal rat ventricular myocytes. This may explain in part the increase in the plateau phase of the action potential and the positive inotropic response of the neonatal myocardium to phenylephrine. This is the first description of an increase in L-type Ca++ current by alpha-1A adrenoceptor activation in neonatal rat ventricular myocytes, and this effect is different from that reported in adult rat myocytes.

Action Potentials↗
PubMed1994

L-channel modulation by alpha-1 adrenoceptor activation in neonatal rat ventricular cells: intracellular mechanisms.

The alpha adrenergic agonist phenylephrine increases the long-lasting Ca++ channel current (L-type Ca++ channel current) in neonatal rat ventricular cells. In these experiments, the intracellular mechanism of the alpha (alpha-1A) adrenergic effect was investigated. Guanosine-5'-O-(2-thiodiphosphate), a G-protein inhibitor, blocked and guanosine-5'-O-(3-thiotriphosphate), a G-protein activator, mimicked the effect of phenylephrine, suggesting that G-proteins are involved in the activation of the alpha-1 adrenoceptor-induced increase in Ca++ channel current. The effect of phenylephrine on the L-type current was not abolished in cells pretreated with pertussis toxin and cholera toxin, indicating that pertussis toxin- and cholera toxin-insensitive G-proteins are coupled to the alpha-1A adrenoceptor. Acute treatment with 4 beta-phorbol-12-myristate and 1-oleoyl-2-acetyl-rac-glycerol, two protein kinase C activators, increased the L-type Ca++ channel current. Staurosporine and prolonged pretreatment with 4 beta-phorbol-12-myristate blocked the effect of phenylephrine. This suggests that protein kinase C activation is involved in the mechanism. The results described in this study suggest that stimulation of the alpha-1A adrenoceptor results in the activation of pertussis toxin- and cholera toxin-insensitive G-proteins which may lead to phosphorylation of Ca++ channel proteins through protein kinase C. The phosphorylation of channel protein results in an increase in the L-type Ca++ channel current in neonatal rat ventricular cells.

Animals↗
PubMed1994

Integrin expression and function in HPV 16-immortalised human keratinocytes in the presence or absence of v-Ha-ras. Comparison with cervical intraepithelial neoplasia.

Keratinocytes express several receptors of the integrin family which regulate both adhesion and differentiation. We have investigated whether HPV immortalisation, which changes the growth and differentiation properties of keratinocytes, is associated with altered integrin expression or function. We compared two HPV 16-immortalised lines of human keratinocytes, up and vp, with the normal keratinocyte strains, u and v, from which they were derived and with upr, obtained by transfection of up with viral Harvey ras. Immunofluorescence, immunoprecipitation and flow cytometry demonstrated that up and vp had lower levels of integrins than u and v, the reduction in up being greater than in vp. Up and vp also had reduced levels of mRNA encoding the beta 1 integrin subunit. Reduced expression of the alpha 5 beta 1 and alpha 2 beta 1 integrins was correlated with reduced adhesion to fibronectin and collagen in up but not in vp and there were no significant differences between the normal and immortalised cells in adhesion to laminin. Reduced integrin expression was correlated with decreased motility, up showing a greater reduction in motility than vp. Introduction of activated ras into up had no effect on integrin levels, cell motility or tumorigenicity in nude mice; the only difference between up and upr was that upr showed increased adhesion to fibronectin. Examination of eight biopsies of cervical intraepithelial neoplasias with evidence of HPV infection revealed reduced or discontinuous integrin expression in the most severe lesions. We conclude that both in vivo and in culture keratinocytes the impaired differentiation that is associated with the presence of HPV is correlated with reduced integrin expression.

Cell Adhesion↗
PubMed1993

Comparison of the action of two protein kinase C activators on dihydropyridine-sensitive Ca2+ channels in neonatal rat ventricular myocytes.

Ca2+ channels can be modulated by protein kinase C which phosphorylates Ca2+ channel proteins. Two protein kinase C activators, 4 beta-phorbol 12-myristate 13-acetate (PMA) and 1-oleyl-2-acetyl-rac-glycerol (OAG), were used to investigate the effect of protein kinase C activation on dihydropyridine-sensitive Ca2+ channel currents (L-type) in neonatal rat ventricular myocytes using the whole cell version of the patch clamp technique. The results show that both of the activators increased the Ca2+ channel current in myocytes. However, these increases in Ca2+ channel current were different as function of time. Therefore, our results suggest that the temporal factor should be considered when the protein kinase C activators are used in studies of channel modulation.

Animals↗
PubMed1993

Voltage and temperature dependence of single K+ channels isolated from canine cardiac sarcoplasmic reticulum.

The temperature and voltage dependence of gating and conductance of sarcoplasmic reticulum K+ channels (S-R K+) isolated from adult canine hearts were studied using the reconstituted bilayer technique. Fusion of vesicles from this preparation frequently resulted in the incorporation of a single channel. Only bilayers into which a single S-R K+ channel had fused were studied. The three conductance states of the channel, fully open (O2), substate conductance (O1), and closed (C) were studied as a function of voltage (-50 to +50 mV) and temperature (16 to 37 degrees C). Permeation through the O1 state showed the same temperature dependence as the O2 state corresponding to an enthalpy of permeation of 4.1-4.2 kcal/mol, which is similar to that for K+ diffusion through water. As expected, increased temperature increased the frequency of gating transitions and shortened the average dwell time spent in any conductance state. Over the range of 25 to 37 degrees C, the average dwell time spent in the O1, O2, and C states decreased by 44 +/- 11, 36 +/- 13, and 78 +/- 7% (n = 3 to 4 channels), respectively. The ratio of probabilities between the various conductance states was not strongly temperature sensitive. Analysis of the voltage dependence of this channel was carried out at 37 degrees C and revealed that the dwell times of the O1 and O2 states were voltage insensitive and the probability ratio (PO2:PO1) was approximately 7 and was voltage insensitive. Nonlinear least-squares analysis of dwell times revealed that the closed state was biexponential and was thus composed of a fast (Cf) and a slow (C8) component.Tcf was voltage insensitive with an average value of 5.9 ms, whereas tau c was approximately two orders of magnitude slower and was voltage dependent. The voltage dependence of Cs was described by Tau c (ms) = exp(-0.025-(Vm (mV) - 250)).

Animals↗
PubMed1993

[Effects of m-nifedipine and nifedipine given intraduodenally on coronary flow, myocardial oxygen, and carbon dioxide metabolism in dogs].

In anesthetized dogs intraduodenal administration of m-nifedipine (m-Nif) 0.4 mg.kg-1, coronary flow increased from 708 +/- 72 to 880 +/- 150 ml.min-1.kg-1 (+24%) at 5 min, to 1976 +/- 350 ml.min-1.kg-1 (+179%) at 30 min, and to 998 +/- 250 ml.min-1.kg-1 (+41%) at 4 h. At the dose of nifedipine (Nif), coronary flow increased from 778 +/- 91 to 1080 +/- 90 ml.min-1.kg-1 (+39%) at 3 min and to 1836 +/- 280 ml.min-1.kg-1 (+136%) at 90 min. m-Nif was more 43% potent than Nif and the duration of action of m-Nif was longer. m-Nif reduced heart rate by -39%, while Nif reduced only -11%. m-Nif increased coronary sinus O2 content and reduced MVO2, and no difference was seen between these 2 drugs. However, the rate of CO2 production with m-Nif was reduced to a greater degree than that of Nif. The results indicated that m-Nif was more beneficial in alleviating myocardial ischemia than that of Nif.

Animals↗
PubMed1992

Expression of a gene encoding a rabbit sperm membrane protein in mammalian cells.

A general mammalian expression vector designated pSV2-EP was reconstructed by inserting an oligonucleotide fragment into pSV2-dhfr. This vector allowed insertion of cDNAs with EcoRI cohesive ends. The pSV2-EP contains a simian virus 40 (SV40) early promoter, origin for DNA replication, SV40 poly-A site, splicing site, an initiator ATG downstream from the promoter and an EcoRI site for the insertion of cDNA fragment screened from lambda gt11 expression libraries. A recombinant plasmid (pS-VRS-1) was constructed by inserting RSD-1, a cDNA encoding a rabbit sperm tail protein, into the EcoRI site of the pSV2-EP vector. Chinese hamster ovarian (CHO) dhfr-negative cells were cotransformed with pSV2-dhfr and pSVRS-1 by the calcium phosphate method. In selective culture medium without thymidine and hypoxanthine, several cell lines were obtained containing mRNA and DNA that hybridized with RSD-1. One of these transformed cell lines stained intensely with anti-rSMP-B antibodies, demonstrating that the RSD-1 was expressed in the transformed CHO cells.

Animals↗
PubMed1992

Tetrandrine inhibits both T and L calcium channel currents in ventricular cells.

Tetrandrine, a putative Ca2+ channel blocker, is extracted from the Chinese medicinal herb, Radix stephania tetrandrae. In the present study, the whole-cell version of the patch clamp technique was used to investigate the effects of tetrandrine on both T and L calcium channel currents in primary cultured neonatal rat ventricular cells. We show that tetrandrine inhibits both T and L calcium channel currents in ventricular cells. This inhibition of inward Ca2+ currents is concentration dependent and reversible. Tetrandrine does not shift the I-V relationship of the calcium currents. These results clearly demonstrate that tetrandrine acts as a calcium channel antagonist in ventricular cells. Previous data show that tetrandrine may be regarded as a wide-spectrum calcium channel antagonist.

Alkaloids↗
PubMed1992

Amphibian ryanodine receptor isoforms are related to those of mammalian skeletal or cardiac muscle.

The ryanodine receptor (RyR)-Ca2+ release channels of frog skeletal muscle have been purified as 30S protein complexes comprised of two high molecular weight polypeptides. The upper and lower bands of the frog doublet comigrated on sodium dodecyl sulfate polyacylamide gels with the mammalian skeletal and cardiac RyR polypeptides, respectively. Immunoblot analysis showed that a polyclonal antiserum to the rat skeletal RyR preferentially cross-reacted with the upper band, whereas monoclonal antibodies to the canine cardiac RyR preferentially cross-reacted with the lower band of the frog receptor doublet. Immunoprecipitation studies indicated the presence of two homooligomer 30S RyR complexes comprised of either the lower or upper polypeptide band of the frog doublet, and immunocytochemical staining revealed their colocalization in frog gastrocnemius muscle. After planar lipid bilayer reconstitution of the 30S frog RyR, single-channel currents were observed that exhibited a Na+ and Ca2+ conductance and pharmacological characteristics similar to those of the mammalian skeletal and cardiac Ca2+ release channels. These results suggest that amphibian skeletal muscle expresses two distinct RyR isoforms that share epitopes in common with the mammalian skeletal or cardiac RyR.

Animals↗
PubMed1992

Inhibitory action of ethanol on L-type Ca2+ channels and Ca(2+)-dependent guanosine 3',5'-monophosphate accumulation in rat pinealocytes.

It has previously been shown that the K+ potentiation of vasoactive intestinal peptide-stimulated cAMP and cGMP responses was inhibited by ethanol in rat pinealocytes, suggesting an inhibitory action of ethanol on the voltage-dependent Ca2+ channels (VDCC). In this study, using the whole cell version of the patch clamp technique, we found that ethanol reduced the amplitude, but did not change the voltage dependence or the time course of activation or inactivation of the L-type VDCC. The inhibitory effect of ethanol on this current was concentration dependent, and ethanol (100 mM) resulted in a 40% inhibition of this current. However, in fura-2-loaded cells, total increases in intracellular Ca2+ ([Ca2+]i) caused by ethanol and BayK 8644 did not differ from the [Ca2+]i signal caused by BayK 8644 alone, suggesting that the inhibitory action of ethanol on VDCC may not be related to a reduction in [Ca2+]i. Although there was no change in the total [Ca2+]i signal, ethanol (25-200 mM) dose-dependently inhibited the potentiation effects of depolarizing concentrations of K+ and BayK 8644 on the isoproterenol-stimulated cGMP, but not the cAMP, response. Therefore, the cGMP response appears to be more sensitive to the inhibitory action of ethanol, and a site distal to elevation of [Ca2+]i of importance to the potentiation mechanism may be inhibited by ethanol. This was confirmed by the finding that ethanol was effective in inhibiting the A23187 potentiation of isoproterenol-stimulated cGMP response. These results suggest that 1) the L-type VDCC was inhibited by ethanol; 2) the Ca(2+)-mediated potentiation of the isoproterenol-stimulated cGMP response was sensitive to the inhibitory action of ethanol; and 3) although ethanol inhibits the VDCC, it alone cannot explain the inhibitory effect of ethanol on BayK 8644- and K(+)-mediated potentiation of the isoproterenol-stimulated cGMP response.

Animals↗
PubMed1991

Reconstitution of the solubilized cardiac sarcoplasmic reticulum potassium channel. Identification of a putative Mr approximately 80 kDa polypeptide constituent.

Recent evidence has indicated that potassium ion movement through sarcoplasmic reticulum (SR) K+ channels is an important countercurrent for Ca2+ release from SR. We used Chaps-solubilized SR vesicles and sucrose density gradient centrifugation to identify components of the canine cardiac SR K+ channel. To overcome the difficulty of the absence of a high-affinity specific ligand, we have successfully applied the planar lipid bilayer reconstitution technique to identify and functionally assay for the solubilized SR K+ channel. We found that Chaps solubilization of the channel did not change the protein's functional properties. The cardiac SR K+ channel sediments as a 15-20S protein complex. A polypeptide of Mr approximately 80 kDa was found to specifically comigrate with the 15-20S gradient fractions and might be a major constituent of the cardiac SR K+ channel.

Animals↗