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Biomedical subjects

M Z Sun

Publications and source records attributed to M Z Sun.

At least 19 recordsLinked to original sources
PubMed2000

[Inhibition of transmembrane K(+) currents in mammalian ventricular myocytes by antiarrhythmic agent RP62719].

The effect of RP62719 on the inward rectifier K(+) current (I(K1)),transient outward K(+) current (I(to)) and delayed outward K(+) current (I(K)) in isolated cardiac myocytes was determined using the whole cell patch clamp technique in guinea pig and dog. RP62719 decreased I(K1) with an inhibitory concentration 50 (IC(50) ) of 5.0+/-1.0 micromol/L at -100 mV in guinea pig ventricular cells. In dog ventricular myocytes, RP62719 inhibited Ito by 84+/-4.4% with an IC(50) of 1.2+/-0.51 micromol/L at +40 mV. In guinea pig ventricular cells, RP62719 decreased I(K): I(Kstep) by 50.0+/-8.3%%and I(Ktail) by 56.0+/-4.9% at +40 mV, respectively. RP62719 inhibited I(Kstep) with an IC(50) of 4.2+/-0.8 micromol/L and I(Ktail) with an IC(50) of 3.3+/-0.75 micromol/L. Thus it is suggested that the ionic mechanism of antiarrhymic effect by RP62719 may be due to its inhibition of I(K1),I(to) and I(K).

Animals↗
PubMed1999

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of phospholipase A2 and fibrinolytic enzyme, two enzymes obtained from Chinese Agkistrodon blomhoffii Ussurensis venom.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to analyze two enzymes, phospholipase A2 and fibrinolytic enzyme isolated from Chinese Agkistrodon blomhoffii Ussurensis venom. Using sinapinic acid as the matrix, positive ion mass spectra of the enzymes were obtained. In addition to the dominant protein [M + H]+ ions, multimeric and multiply charged ions were also observed in the mass spectra. The higher the concentration of the enzymes, the more multiply charged polymer and multimeric ions were detected. Our results indicate that MALDI-TOFMS can provide a rapid and accurate method for molecular weight determination of snake venom enzymes. Mass accuracies of 0.1 and 0.3% were achieved by analysis of highly dialyzed phospholipase A2 and fibrinolytic enzyme, and these results are much better than those obtained using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. MALDI-TOFMS thus provides a reliable method to determine the purity and molecular weight of these enzymes, which are of potential use as therapeutants.

Agkistrodon↗
PubMed1997

[Effect of microinjection of GABA into the caudate nucleus on electrical discharges of nociceptive neurons in caudate nucleus of rat].

The characteristics of glass microelectrode recorded electrical activity of nociceptive neurons in the caudate nucleus elicited by microinjection of GABA and blockage by picrotoxin (PIC) were studied in 53 Wistar rats. The results showed that GABA (25, 50, 100 micrograms/2 microliters every 2 min) inhibited the activity of pain excitation neurons (PEN), as shown by decreased frequency and increased latency, but enhanced the activity of pian, inhibition neurons (PIN), as shown by shortened duration and increased discharge frequency. Both activities are highly dose-dependent and could be blocked by PIC (i.p. 250 micrograms, 1 ml/1 min).

Animals↗
PubMed1996

Inhibitory effect of tetrahydropalmatine on calcium current in isolated cardiomyocyte of guinea pig.

AIM: To study the effect of tetrahydropalmatine (THP) on calcium channels in ventricular single cells of guinea pig heart. METHODS: Patch-clamp technique (whole cell recording) was used to observe calcium current in ventricular myocytes. RESULTS: THP decreased ICa in ventricular myocytes with a dose and frequency-dependent manner. THP (0.1, 1, and 10 mumol.L-1) decreased ICa from 1.15 +/- 0.22, 0.91 +/- 0.18, and 1.60 +/- 0.42 nA (control) to 0.9 +/- 0.21 (P < 0.01), 0.56 +/- 0.21 (P < 0.01), and 0.83 +/- 0.21 nA (P < 0.05), respectively, number of cells is five in each group (n = 5), and the rates of the depression of ICa were 22%, 38%, and 48%, respectively. The effect was easily reduced by washing the cell with the Tyrode's solution. The current-voltage relation curve showed that the potential producing peak value of ICa was 0 mV at which THP had the most markedly inhibited action on ICa. When the stimulating frequency was changed, ICa varied in a frequency-dependent manner 5 min after THP was given, and the inhibition of THP was stronger at 2 Hz than that at 0.1 Hz. CONCLUSION: THP possessed a Ca2+ channel blocking effect.

Action Potentials↗
PubMed1993

Reversal of electroacupuncture tolerance by CCK-8 antiserum: an electrophysiological study on pain-related neurons in nucleus parafascicularis of the rat.

Two varieties of neurons were found in nucleus parafascicularis (pf) of the rat: one responds to noxious stimuli with an increase in firing (pain-excited neuron, PEN), the other with a decrease in firing (pain-inhibited neuron, PIN). Electroacupuncture (EA) has been shown to suppress PEN and excite PIN, which can be taken as an electrophysiological index for EA analgesia. This effect of EA subsided after prolonged (6 h) EA stimulation, suggesting the development of tolerance to EA. Intracerebroventricular (icv) injection of CCK-8 antiserum aiming at neutralizing endogenously released CCK-8 resulted in a complete restoration of the EA effect. Normal rabbit serum was not effective. CCK-8 antiserum per se did not affect the firing pattern of the PEN or PIN in nontolerant rat. The results obtained from single neuron recording in anesthetized animals thus confirmed those obtained in intact animals using the tail flick as the end point, implying that an excess of endogenously released CCK-8 may constitute one of the mechanisms for the development of EA tolerance.

Animals↗
PubMed1993

[Hyperinsulinemia in obesity and diseases of internal medicine].

We analysed fasting serum insulin levels and its correlation with common internal medical diseases in 91 cases with obesity (BMI > 24) and that in 76 nonobese cases. The mean fasting serum insulin level in obese group was higher significantly than that in nonobese group (P < 0.001). The incidences of hypertension, coronary heart disease, cerebrovascular disease, non-insulin-dependent diabetes mellitus, hypercholesterolemia, hypertriglyceridemia, combined hyperlipidemia and serum low level of HDL-C in obese group were also higher significantly than that in nonobese group (P < 0.05 and < 0.01 respectively). The main cause of many medical diseases coexisted with obesity is hyperinsulinemia. We think that the first choice of therapy to this kind of diseases should be to reduce the body weight and to decrease the insulin resistance.

Adult↗
PubMed1992

Tenascin and fibronectin distribution in human normal and pathological synovium.

Tenascin is a glycoprotein found mainly in the extracellular matrix of developing and malignant tissues. The distribution of this molecule in normal and pathological synovia from patients with osteoarthritis (OA) and rheumatoid arthritis (RA) was investigated by indirect immunofluorescence utilizing specific monoclonal antibodies. The same technique was used to study total fibronectin (tFn) in synovial tissues as well as ED-A and ED-B containing fibronectin (Fn) isoforms (A-Fn, B-Fn), generated by alternative splicing of pre-mRNA. Tenascin was found in normal synovium just beneath the whole lining cell layer. However, a higher density and spreading pattern of distribution was observed in OA and RA sections. A-Fn and B-Fn isoforms were prominent and widespread throughout the normal synovial lining; in hypercellular synovial lining (in RA and OA samples), A-Fn and B-Fn were also observed spreading in the sublining, as well as tFn.

Antibodies, Monoclonal↗
PubMed1992

[The effect of lovastatin in the treatment of primary hypercholesterolemia].

The effect of Lovastatin, an HMG. CoA reductase inhibitor, on serum lipids and apolipoproteins was studied in 40 cases of primary hypercholesterolemia in a 4-month period of treatment. The level of serum lipids did not change significantly after a 35-day period of placebo treatment as compared with that of the baseline (P greater than 0.5). The patients then took Lovastatin with the evening meal in a daily dose from 20 to 80 mg for 3 months. The results were as follows: Lovastatin reduced significantly the mean serum level of total cholesterol (TC) by 31.5% (P less than 0.001), LDL-C by 39.8% (P less than 0.001), Apo-B by 27.3% (P less than 0.002), and the ratio TC/HDL-C by 35.9% (P less than 0.01). It also reduced the mean serum level of triglycerides (TG) by 22.1% (P greater than 0.05) and increased that of HDL-C by 6.3% (P greater than 0.2) and Apo-AI by 1.6% (P greater than 0.5), but without much significance. The drug was well tolerated by all the patients. Transient elevation of CPK was noticed in 2 patients and AKP in one patient. 7 patients complained of gastrointestinal discomfort. All these side effects did not necessitate stop of the medication. We are, therefore, of the opinion that Lovastatin is an effective agent for lowering the serum level of TC, LDL-C and Apo-B.

Adult↗
PubMed1990

Simultaneous electric activities of pain-excitation and pain-inhibition neurons in nucleus parafascicularis of thalamus in rats during acute morphine tolerance.

When acute morphine-tolerated rat was administered by ip morphine (10 mg/kg) which was effective before the acute tolerance to morphine, both the inhibitory effect of morphine on the electric discharges of pain-excitation neurons (PEN) in nucleus parafascicularis (PF) and the excitatory effect of morphine on the electric activities of pain-inhibition neurons (PIN) were simultaneously weakened, or even vanished. If a large dose of morphine (20 mg) was given ip, the modulating action of morphine on simultaneous electric discharges of PEN and PIN reappeared. It is obvious that the phenomenon of acute morphine tolerance and the antagonism to morphine tolerance can be explicitly expressed on the level of central neurons.

Animals↗
PubMed1989

[The influence of GABA injected into cerebral ventricle on electrical activities of pain-excitation neurons and pain-inhibition neurons in nucleus parafascicularis of the thalamus of rats].

The influence of intraventricular injection of GABA on electrical activities of PEN and PIN in nucleus parafascicularis of the thalamus of rats was studied. The results showed that GABA could significantly inhibit the electrical discharges of PEN and increase the electrical discharges of PIN. So it was believed that intraventricularly injected GABA could antagonize or partly antagonize the excitatory action of noxious stimuli and might thus produce analgesia.

Animals↗
PubMed1984

The simultaneous discharges of two neurons in N. Pf and RF and the influences on them by stimulating central gray matter.

This paper employs the method of simultaneous recording of the electric discharges of two neurons with two microelectrodes to study the interrelationship of simultaneous electric activities of pain excitation neurons (PEN) and pain inhibition neurons (PIN) in N. parafascicularis (Pf) of thalamus and reticular formation (RF) of midbrain in 42 rats. The results prove: (i) There are both PEN and PIN in RF in midbrain and they act coordinately; (ii) noxious messages may simultaneously act on PEN and PIN in N. Pf and RF, and the reciprocal coordination of electric activities of these two kinds of neurons is very obvious; (iii) stimulating central gray matter or injecting morphine may weaken the activities of PEN simultaneously, with the opposite effects on PIN.

Action Potentials↗