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Biomedical subjects

J Y Pan

Publications and source records attributed to J Y Pan.

At least 37 records · Page 2Linked to original sources
PubMed1997

Synthesis and effect of nonhydrolyzable xanthosine triphosphate derivatives on prenylation of Rab5D136N.

A novel and convenient method for nucleoside triphosphate synthesis was applied to the preparation of potentially nonhydrolyzable xanthosine triphosphate derivatives. The N-methylimidazolide of xanthosine 5'-monophosphate reacted rapidly with methylenediphosphonic acid and imidodiphosphonic acid to give xanthosine 5'-(beta, gamma-methylene)triphosphate and xanthosine 5'-(beta, gamma-imido)triphosphate, respectively, in good yields. Both compounds inhibited the xanthosine-diphosphate-dependent prenylation of a mutant of Rab5, Rab5D136N, the nucleotide specificity of which had been converted from GTP to xanthosine triphosphate. The results indicate that xanthosine 5'-(beta, gamma-methylene)triphosphate and xanthosine 5'-(beta, gamma-imido)triphosphate bound to the mutant protein with similar affinities and were not hydrolyzed under the assay conditions. These novel derivatives may be useful tools for the study of the role of individual GTPases mutated to xanthosine triphosphate specificity in the background of other GTP-binding proteins.

GTP Phosphohydrolases↗
PubMed1997

[Changes in the expression of alpha- and beta-myosin heavy chain gene during the development of renal hypertension in rats].

The changes in the expression of cardiac alpha- and beta-myosin heavy chain (MHC) gene of the left ventricle were investigated in two-kidney, one-clip (2K1C) renal hypertensive rats. The results were as follows: (1) When blood pressure was increased, the left ventricle became hypertrophic, alpha-MHC gene expression was reduced and beta-MHC gene expression was increased in 2K1C renal hypertensive rats. (2) When the animal was treated with captopril, angiotensin converting enzyme inhibitor 4 W after operation and then 8 W with removal of the ischemic kidney, the blood pressure was decreased with attendant regression of left ventricular hypertrophy, while the increase in beta-MHC mRNA level was attenuated and the inhibition of alpha-MHC mRNA level was reduced. The above results suggest that the rise in arteral pressure is an important factor in the left ventricular hypertrophy and the MHC gene switch. Renin angiotension system may be involved in the cardiac hypertrophic and MHC gene switch during the development and maintenance of 2K1C renal hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Influence of Mg2+ on the structure and function of Rab5.

Mg2+ inhibits GDP release from Rab5WT but not from Rab5S34N, a mutant lacking Ser34 critical for Mg2+ coordination in the nucleotide binding pocket. Thus, inhibition of GDP release is apparently exerted via coordination of Mg2+ between Rab5 and GDP. Mg2+ also induces conformational changes in Rab5WT, demonstrated by increased tryptophan fluorescence intensity and a red shift in lambda max for the GDP-bound protein. Mg(2+)-induced fluorescence changes are not observed for Rab5S34N. The correlation between Mg2+ effects on nucleotide exchange and the fluorescence properties of Rab5 suggests that a conformation promoted through Mg2+ coordination with Ser34 also contributes to inhibition of GDP release. The role of structural changes in GDP release was investigated using C- and N-terminal truncation mutants. Similar to Rab5WT, Mg2+ inhibits GDP release and alters the fluorescence of Rab5(1-198) but only partially inhibits release from Rab5(23-198) and fails to induce changes in the latter's fluorescence properties. Since Rab5(23-198) maintains Ser34 necessary for Mg2+ coordination, the lack of Mg(2+)-induced fluorescence changes suggests a requirement for the N-terminal domain to promote a conformation blocking GDP release. A model for mechanisms of interaction between Ras-like proteins and their exchange factors is proposed.

Amino Acid Sequence↗
PubMed1996

[Expression of c-fos mRNA induced by pressure overload in the left ventricle].

In the present study the effect of pressure overload on the expression of protooncogene c-fos in the left ventricle was investigated in rats with abdominal aorta constriction. It was found that a remarkable expression of c-fos was induced by pressure overload and the expression was greatly attenuated by angiotensin converting enzyme inhibitor captopril. In the pressure overload group the angiotensinogen mRNA level was found increased. The above results suggest that angiotensin II is involved in the expression of c-fos due to pressure overload.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

GDP dissociation inhibitor serves as a cytosolic acceptor for newly synthesized and prenylated Rab5.

In vitro synthesis and post-translational prenylation of Rab5 is accomplished using reticulocyte lysate supplemented with prenyl precursors (Sanford, J. C., Pan, Y., and Wessling-Resnick, M. (1993) J. Biol. Chem. 268, 23773-23776). When Rab5 is translated in the presence of biotin-lysine-tRNA, it incorporates biotin-lysine into its peptide backbone and is efficiently prenylated; since this modification is dependent on guanine nucleotide binding, biotin-Rab5's functional integrity must be maintained. Prenylated biotin-Rab5 associates with a 45-kDa reticulocyte GDP dissociation inhibitor (GDI), sedimenting as a approximately 70-kDa particle on 5-20% sucrose density gradients. The GDI-Rab5 complex can be captured using streptavidin-linked agarose beads. Only Rab5 peptides that are substrates for prenylation are found to cosediment with the lysate GDI on sucrose gradients. Post-translational association of Rab5 and GDI is a novel finding, since previous reports suggested Rab5 remains associated with Rab escort protein (REP) after prenylation (Alexandrov, K., Horiuchi, H., Steele-Mortimer, O., Seabra, M. C., and Zerial, M. (1994) EMBO J. 13, 5262-5273). Since post-translational prenylation is catalytically mediated by REP, our study suggests that a complex between Rab5 and this factor is transient in nature. Thus, newly synthesized and prenylated Rab5 is most likely escorted to its target membrane by a GDI acceptor molecule. Biotin-Rab5 provides a novel tool for future efforts to capture and characterize additional accessory factors required for Rab protein function in vesicle transport.

Animals↗
PubMed1995

Effect of guanine nucleotide binding on the intrinsic tryptophan fluorescence properties of Rab5.

To gain further insight into structural elements involved in Rab5 function, differences in the intrinsic tryptophan fluorescence of the GDP- and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)-bound forms of the protein were examined. When excited at 290 nm, Rab5 displays emission maxima at 339.7 nm for the GDP-bound and 336.7 nm for the GTP gamma S-bound forms. The tryptophan fluorescence intensity is quenched by approximately 25% in the GTP gamma S-bound form relative to the GDP-bound conformation. Variant Rab5 molecules were created by site-directed mutagenesis to convert the protein's two tryptophans to phenylalanine residues. Fluorescence studies reveal that the observed changes upon GDP/GTP gamma S exchange are due to a blue shift in the emission spectra for both Trp74 (342.0 to 339.5 nm) and Trp114 (335.3 to 333.7 nm) and fluorescence quenching of Trp114. Consistent with the blue shift in the emission spectra, both tryptophans are more resistant to oxidation by N-bromosuccinimide in the GTP gamma S-bound state. These data indicate that both of Rab5's tryptophans are brought into a more sequestered, hydrophobic environment upon conformational changes promoted by guanine nucleotide exchange. Since Trp74 lies adjacent to Rab5's cognate switch II domain, local conformational changes would be predicted based on the known structure of Ras. However, Trp114 lies within a region of Rab5 potentially related to the switch III domain unique to heterotrimeric G alpha t. Thus, changes in the fluorescence properties of Trp114 upon guanine nucleotide exchange suggest that Rab proteins may have structure-function relationships similar to those described for heterotrimeric GTP-binding proteins.

Amino Acid Sequence↗
PubMed1995

Functional and structural interactions of the Rab5 D136N mutant with xanthine nucleotides.

Rab5 is a Ras-related GTPase which regulates endosomal fusion. The D136N mutant of Rab5, which was predicted to switch specificity from guanine to xanthine nucleotides, was expressed in E. coli, extracted with urea, purified by column chromatography, and refolded by stepwise dialysis against buffer containing XDP. The purified protein bound xanthine nucleotides with considerably higher affinity than guanine nucleotides. In vitro prenylation of the mutant protein was highly dependent on xanthosine diphosphate. In contrast, both the wild type and mutant proteins were protected from proteolysis equally well by non-cognate and cognate triphosphate nucleosides at high concentration. The D136N Rab5 mutant appears to be a valuable reagent in conjunction with xanthine nucleotides for the study of protein-nucleotide interactions in systems in which multiple GTPases are active, although interactions with non-cognate nucleotides should be evaluated if they are present at high concentration.

Base Sequence↗
PubMed1995

[The role of G protein in Leu-enkephalin induced Ca2+ release from intracellular pool in myocytes].

The mechanism underlying Leu-enkephalin (LEK) induced increase of the intracellular concentration of free calcium ([Ca2+]i) in rat ventricular myocytes was investigated by using fura-2 AM as a calcium indicator. The results were as follows: LEK (60 mumol/L) elevated [Ca2+]i in ventricular myocytes no matter whether extracellular calcium was removed or not. However, the effect was no longer observed when the calcium in the intracellular pool was depleted by caffeine (5 mmol/L). The LEK effect could also be blocked by naloxone (100 mumol/L), pretreatment of the cells with PTX (200 ng/L) 8-10 h or procain (2 mmol/L). The results suggest that the LEK effect is mediated by coupling of G-protein with delta-receptor that induced Ca2+ release from the intracellular pool in myocytes.

Animals↗
PubMed1995

[Angiotensin II induces c-fos and c-myc proto-oncogene expression in the left ventricle].

In the present study, the effects of angiotension II on the expression of protooncogene c-fos and c-myc in the left ventricle were investigated on Langedorff heart preparations. It was observed that angiotensin induced both c-fos and c-myc expression in a dose-dependent manner and the c-fos expression showed an earlier appearance than c-myc. All these induced expressions were blocked by a Angiotensin II receptor antagonist saralasin. The Angiotensin II induced expression of c-fos was also blocked by TTX, but the c-myc gene expression was unaffected.

Angiotensin II↗
PubMed1995

[Reduction of incidence of ischemia-reperfusion induced ventricular fibrillation by captopril].

To investigate the role of catecholamine and prostacyclin in ischemia reperfusion-induced ventricular fibrillation, experiments were performed in rat hearts using methods of radioimmunoassay and fluorohistochemistry. Regional myocardial ischemia was induced by ligation of the left coronary artery followed by reperfusion. In the ischemia reperfusion group, ventricular fibrillation during reperfusion took place in 78% of the hearts. In the group pretreated with captopril, the incidence of ventricular fibrillation decreased significantly (65.5%). In comparison with the ischemia reperfusion group, myocardial catecholamine content and 6-keto-PGF1 alpha of the captopril group were significantly increased (P < 0.01) while thromboxane B2 (TxB2) and TxB2/6-keto-PGF1 alpha were decreased (P < 0.01). In Ang II group, infusion of angiotensin II reversed the protective effect of captopril and restored the incidence of ventricular fibrillation (85%), while myocardial catecholamine content was not different from the ischemia reperfusion group (P > 0.05). Above results suggest that reduction of the incidence of ischemia reperfusion-induced ventricular fibrillation by captopril may be due to its inhibition on angiotensin II production with consequent reduction of the release of myocardial catecholamine, suppression of TxB2 and promotion of PGI2 synthesis.

6-Ketoprostaglandin F1 alpha↗
PubMed1993

[Effect of stimulation of renal afferent nerves on plasma cortisol concentrations].

The effect of stimulation of the renal afferent nerve (RAN) on plasma cortisol concentrations before and after lesions of paraventricular nuclei of hypothalamus (PVN) in chloralose-anesthetized cats was investigated. In animals with intact arterial baroreceptor stimulation of RAN did not significantly change the plasma cortisol concentration. However, the same stimulation elicited a significant increase in plasma cortisol concentration when the baroreceptor was denervated. Lesioning of bilateral PVN by kainic acid could abolish the cortisol response to stimulation of RAN. These data indicate that arterial baroreceptor reflex inhibited the cortisol response to stimulation of RAN and that PVN may be involved in the cortisol response to stimulation of RAN.

Afferent Pathways↗
PubMed1992

[Different changes in renal sympathetic nerve activity and adrenal sympathetic nerve activity produced by hemorrhage].

The present study was undertaken to investigate the changes in renal sympathetic nerve activity (RSNA) and adrenal sympathetic nerve activity (AdSNA) due to acute hemorrhage in anesthetized rabbits. The animals were bled to a mean arterial pressure (MAP) of 5.3 kPa within 10 minutes from the femoral artery. Acute hemorrhage elicited a biphasic responses of RSNA with an initial excitation and a late inhibition during hemorrhage. But hemorrhage only induced a lasting excitation in AdSNA which could be abolished by sino-aortic denervation (SAD). Bilateral vagotomy either before or after hemorrhage could reverse the late inhibition in RSNA, but did not abolish the excitation in AdSNA. Intravenous injection of naloxone or microinjection of naloxone into rostral ventrolateral medulla (RVLM) could reverse the late inhibition in RSNA, but had no significant effect on the initial excitation in RSNA and AdSNA during hemorrhage. Hemorrhage-induced heart (HR) change was similar that in RSNA, but could not be reversed by naloxone. These results indicate that the late inhibition in RSNA is mediated by inputs from vagus nerves and opiate peptide, particularly that in RVLM, and the excitation in AdSNA during hemorrhage is related to arterial baroreceptor reflex.

Adrenal Glands↗
PubMed1992

[Effects of stimulation of renal afferent nerve on renal excretion of water, sodium and potassium].

The present study was designed to investigate the effect of stimulation of the renal afferent nerve (RAN) on renal excretory function and its mechanism. In pentobarbital-anesthetized, sino-aortic denervated and vagotomized (SAD+VD) cats, stimulation of the RAN caused a significant rise in arterial pressure. In the denervated kidney urine volume (Vu) and sodium excretion (UNa V) were greatly increased, no changes in potassium excretion (UK V) and glomerular filtration rate (GFR) were observed. In the innervated kidney, UNa V was greatly increased, but Vu, UK V and GFR were not different from those observed during the control period. When arterial pressure was held constant at the control level, stimulation of the RNA reduced the Vu, UK V of both the innervated and denervated kidneys and GFR in the innervated but not in the denervated kidney. Transection of spinal cord at C7 level did not abolish the changes in Vu, UNa V, and UK V in the innervated kidney, but completely eliminated the changes in the excretory function in the denervated kidney. These data suggest that when arterial pressure is controlled, stimulation of the RAN causes a decrease in Vu, UNa V, UK V in SAD+VD cats and that these responses in the innervated kidney can be performed at the spinal level.

Afferent Pathways↗
PubMed1991

[Role of paraventricular nucleus of hypothalamus in pressor response to stimulation of renal afferent nerve in cats].

The purpose of this study is to investigate the role of paraventricular nucleus of the hypothalamus (PVN) and alpha 1 adrenergic receptor of PVN in the pressor responses to stimulation of renal afferent nerve in alpha 1-chloralose-anesthetized cats with carotid sinoaortic denervation and vagotomy. The pressor response to stimulation of renal afferent nerve consisted of a primary and a second components. The primary component response was completely blocked while the second component was not blocked by autonomic blocking agents (hexomethonium and atropine). Bilateral lesions of PVN greatly attenuated the pressor response before and after autonomic blockade. Intracerebroventricular and PVN injection alpha 1, adrenergic antagonist (prazosin) significantly decreased in the pressor response to stimulation of renal afferent nerve. These results indicate that paraventricular nucleus of the hypothalamus and alpha 1 adrenergic receptors in central nervous system, especially in PVN, play an important role in the pressor responses to stimulation of renal afferent nerve.

Afferent Pathways↗
PubMed1991

[Effect of hypertonic NaCl solution on arterial pressure compensation after hemorrhage in rats].

Rats were bled within 5 min in lowering mean arterial pressure (MAP) to 25 mmHg and were subsequently infused intravenously with hypertonic (7.5% NaCl) or normal saline in a volume equal to 10% of the amount of the lost blood. Intravenous infusion of hypertonic saline significantly facilitated posthemorrhagic recovery of MAP, which was markedly attenuated by 6-hydroxydopamine or Captopril. When these two drugs were used together, the attenuation effect was complete. While hypertonic saline significantly increased plasma Na+ concentration, normal saline only gave rise to a decrease. Intracerebroventricular injection of hypertonic NaCl solution also facilitated the recovery of MAP significantly. These results suggest that after hemorrhage increased plasma Na+ concentration following i.v. of a small amount of hypertonic saline may act on the central nervous system and activate sympathetic nervous system and renin angiotensin system to facilitate a rapid recovery of MAP.

Animals↗
PubMed1991

[Observation on the contraction process of ovarioles of Anopheles sinensis and Anopheles anthropophagus after oviposition].

In order to know the process of ovariole contraction after oviposition in Anopheles sinensis and An. Anthropophagus, and to determine the relationship between the ovariole contraction and the physiological age, the observation was conducted in 1988. The laboratory-reared female mosquitoes after 3-5 days of eclosion were fed with mouse blood and were kept in separate finger tubes for oviposition. After oviposition, the mosquitoes were dissected at different time. 30 ovarioles for each mosquito were examined and recorded by Detinova's method. A total number of 75 An. sinensis with 2,262 ovarioles and 87 An. anthropophagus with 2,591 ovarioles were examined after first oviposition. The duration for ovariole contraction in the phase of A,B,C,D,E was 1, 3-6, 9-14, 15-18 and 21h respectively. A total number of 40 An. sinensis with 1,337 ovarioles and 34 An. anthropophagus with 1,099 ovarioles were examined after third oviposition. The duration for ovariole contraction in the phase of A,B,C,D,E was 1, 3-9, 12-15, 18 and 21h respectively. E phase can be found in 21-24h after oviposition. There were 29.3% and 38.0% ovarioles in C and D phase for first oviposition while 48.4% and 46.0% ovarioles in C and D phase for third oviposition. It was found that the contraction occurred first in breadth and then in length.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

[Effects of morphine of different concentrations on myocardial action potential].

The effects of morphine at different concentrations on myocardial action potential were studied in isolated right ventricular papillary muscles of the guinea pig. It was observed that morphine at low concentrations (0.2-1.6 mumol/L) shortened the action potential duration (ADP) and effective refractory period (ERP) in a concentration dependent manner. These effects could be abolished by naloxone (1 mumol/L), phentolamine, tetraethylammonium (TEA) and cesium chloride (Cs+), but not by verapamil. On the other hand, morphine at high concentrations (15-120 mumol/L) prolonged ADP and ERP in a concentration dependent manner. The effects were unaffected by low dose of naloxone (1.2 mumol/L) but were abolished by high dose of naloxone (10 mumol/L), phentolamine, TEA, Cs+ and verapamil. These results suggest that morphine at low and high concentrations might stimulate different subtypes of opioid receptors. The effects of morphine in low concentrations are associated with the activation of potassium channel, whereas the effects of morphine at high concentrations are associated with the activation of potassium channel, calcium channel or calcium activated potassium channel. The action of opioid receptor was closely related to alpha adrenoreceptors.

Action Potentials↗