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Biomedical subjects

B S Pan

Publications and source records attributed to B S Pan.

24 records · Page 2Linked to original sources
PubMed1989

Removal of tropomyosin overlap modifies cooperative binding of myosin S-1 to reconstituted thin filaments of rabbit striated muscle.

Cooperative binding of myosin S-1.ADP to regulated F-actin was previously reported and has been interpreted by a two-state model in which an important source of cooperativity is nearest neighbor interactions between the 7-actin.tropomyosin (TM).troponin units (functional units) (Hill, T.L., Eisenberg, E., and Greene, L. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 3186-3190). It has been postulated that the head-to-tail overlap between adjacent TM molecules is the structural basis of the nearest neighbor interactions. We tested the hypothesis by examining S-1.ADP binding to reconstituted regulated F-actin containing either intact TM or nonpolymerizable TM from which the COOH-terminal 11 residues were removed. In the absence of Ca2+, substitution of nonpolymerizable TM for TM reduced significantly the slope of the steeply rising phase of the sigmoidal S-1.ADP binding curve. Nevertheless, considerable residual cooperativity remained. Analysis of the data using the two-state model of Hill et al. suggests that removal of TM overlap abolishes nearest neighbor interactions, while the concerted change of the state of 7 actins in a functional unit can account for the residual cooperativity.

Actin Cytoskeleton↗
PubMed1989

[Effect of dexamethasone on Coxsackie B-2 virus-infected rat beating heart cells in culture].

The effects of dexamethasone (Dex) on cultured rat beating heart cells infected with 100 TCID-50 Coxsackie virus B-2 (CB2V) were observed. The beating % began to decrease in the infected group 2 or 3 d post-challenge. Meanwhile, the cytopathic effect (CPE) appeared rapidly from 1+ to 3+. In the infected and Dex-treated group 1 h after inoculation, the beating % and CPE in the whole flask were significantly higher and less, respectively, than that in the group infected (P less than 0.05) at the same intervals. At 5 d after challenge, the beating % in the whole flask was significantly higher than that in the infected group. The cardiac enzyme-aspartate aminotransferase (AST) in the infected group was higher than that in the infected and Dex-treated group (P less than 0.01) through 3-5 d post-challenge. Moreover, the AST levels in these 2 groups were also higher than that in the uninfected group, Dex control group at the same intervals (P less than 0.01). Ultrastructural findings were parallel to the results of CPE through 1-5 d post-challenge in these 4 groups. It is suggested that the protective effect of Dex on cultured beating heart cells infected with CB2V occurred in the early stages after infection. It is surmised that steroids can probably save the lives of patients with severe myocarditis if the conventional therapy for protecting the myocardium and improving immunity were administered together.

Animals↗
PubMed1987

Calcium-binding properties of troponin C in detergent-skinned heart muscle fibers.

In order to obtain information with regard to behavior of the Ca2+ receptor, troponin C (TnC), in intact myofilament lattice of cardiac muscle, we investigated Ca2+-binding properties of canine ventricular muscle fibers skinned with Triton X-100. Analysis of equilibrium Ca2+-binding data of the skinned fibers in ATP-free solutions suggested that there were two distinct classes of binding sites which were saturated over the physiological range of negative logarithm of free calcium concentration (pCa): class I (KCa = 7.4 X 10(7) M-1, KMg = 0.9 X 10(3) M-1) and class II (KCa = 1.2 X 10(6) M-1, KMg = 1.1 X 10(2) M-1). The class I and II were considered equivalent, respectively, to the Ca2+-Mg2+ and Ca2+-specific sites of TnC. The assignments were supported by TnC content of the skinned fibers determined by electrophoresis and 45Ca autoradiograph of electroblotted fiber proteins. Dissociation of rigor complexes by ATP caused a downward shift of the binding curve between pCa 7 and 5, an effect which could be largely accounted for by lowering of KCa of the class II sites. When Ca2+ binding and isometric force were measured simultaneously, it was found that the threshold pCa for activation corresponds to the range of pCa where class II sites started to bind Ca2+ significantly. We concluded that the low affinity site of cardiac TnC plays a key role in Ca2+ regulation of contraction under physiological conditions, just as it does in the regulation of actomyosin ATPase. Study of kinetics of 45Ca washout from skinned fibers and myofibrils revealed that cardiac TnC in myofibrils contains Ca2+-binding sites whose off-rate constant for Ca2+ is significantly lower than the Ca2+ off-rate constant hitherto documented for the divalent ion-binding sites of either cardiac/slow muscle TnC or fast skeletal TnC.

Animals↗
PubMed1986

An endogenous ligand from human CSE for the phencyclidine receptor.

A fraction which potently and specifically competed with 3H-PCP binding to rat membranes was isolated from human CSF. This substance ran just before the salts in Sephadex G-25 column and was eluted with low concentrations of acetonitrile in reverse phase HPLC, predicating that it may be a small hydrophilic compound with a MW. of less than 1,000 daltons.

Animals↗
PubMed1984

The effect of acidic pH on the ATPase activity and troponin Ca2+ binding of rabbit skeletal myofilaments.

We compared the effect of reductions in pH from 7.0 to 6.5 and to 6.2 on Mg-ATPase activity and Ca2+ binding of rabbit psoas myofilaments. The amounts of Ca2+ bound attributable to myofilament whole troponin complexes (Tn) were determined from studies on Tn free (desensitized) myofibrils and from measurements of the myofilament Ca2+ binding subunit of Tn content (0.55 +/- 0.10 nmol/mg of myofilament protein). The myofibrillar Mg-ATPase activity was half-maximal at the -log molar free Ca2+ concentration (pCa) 5.83 at pH 7.0, 5.54 at pH 6.5, and 5.43 at pH 6.2 Maximal ATPase activity was the same at the three pH values as was the ATPase activity of desensitized myofibrils. The amounts of Ca2+ bound to myofibrils or chemically skinned fibers as a function of pCa decreased as pH was lowered from 7.0 to 6.5 and to 6.2 in a manner predicted from the pH-induced shifts in Mg-ATPase activity as a function of pCa. The alterations in myofibrillar ATPase activity and Ca2+ binding associated with the acidic pH values occurred whether or not EGTA was used to buffer the free Ca2+ concentration. Moreover, lowering the pH from 7.0 to 6.2 reduced Ca2+ binding to myofilament Tn whether or not the fibers and myofibrils were in rigor. Our data indicate that the effects of acidic pH on myofilament ATPase activity and Ca2+-binding are related to a reduction in the affinity of Ca2+-binding sites on Tn.

Adenosine Triphosphatases↗