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S T Li

Publications and source records attributed to S T Li.

51 records · Page 3Linked to original sources
PubMed1982

Characterization of calcium binding to brush-border membranes from rat duodenum.

The Ca2+-binding properties of isolated brush-border membranes at physiological ionic strength and pH were examined by rapid Millipore filtration. A comprehensive analysis of the binding data suggested the presence of two types of Ca2+-binding sites. The high-affinity sites, Ka = (6.3 +/- 3.3) X 10(5) M-1 (mean +/- S.E.M.), bound 0.8 +/- 0.1 nmol of Ca2+/mg of protein and the low-affinity sites, Ka = (2.8 +/- 0.3) X 10(2) M-1, bound 33 +/- 3.5 nmol of Ca2+/mg of protein. The high-affinity site exhibited a selectivity for Ca2+, since high concentrations of competing bivalent cations were required to inhibit Ca2+ binding. The relative effectiveness of the competing cations (1 and 10 mM) for the high-affinity site was Mn2+ approximately equal to Sr2+ greater than Ba2+ greater than Mg2+. Data from the pH studies, treatment of the membranes with carbodi-imide and extraction of phospholipids with aqueous acetone and NH3 provided evidence that the low-affinity sites were primarily phospholipids and the high-affinity sites were either phosphoprotein or protein with associated phospholipid. Two possible roles for the high-affinity binding sites are suggested. Either high-affinity Ca2+ binding is involved with specific enzyme activities or Ca2+ transport across the luminal membrane occurs via a Ca2+ channel which contains a high-affinity Ca2+-specific binding site that may regulate the intracellular Ca2+ concentration and gating of the channel.

Animals↗
PubMed1977

On the state of anionic groups of demineralized matrices of bone and dentine.

Calcium-binding and biochemical studies have been applied to characterize the state of the carboxylate and protein-bound phosphate groups in the EDTA-demineralized matrices of rat bone and dentine. The organic phosphate and carboxylate content of demineralized bone is virtually identical to that of purified steer skin collagen whereas demineralized dentine has a significantly higher phosphate and carboxylate content, presumably due to the presence of an acidic non-collagenous phosphoprotein. Two classes of calcium-binding sites can be detected in demineralized bone, demineralized dentine, and purified, reconstituted collagen. The number of strong calcium-binding sites correlates with the number of protein-bound phosphate groups. Depending on the preparative procedure, seven to nine such sites (per collagen molecule) are present in dentine, and one to two in the purified reconstituted collagen and in bone. The binding constant for the dentinal sites (1.1 X 10(4) M-1), however, is 20 times greater than that for bone or reconstituted collagen fibrils from skin. We tentatively conclude that the strong calcium-binding site in bone and reconstituted collagen is of the form protein-PO-4Ca++ whereas in dentine it is of the form protein (formula: see text); the weak binding sites in bone and dentine are of the form protein-COO-Ca++; and that approximately 160 of the 217 carboxylate groups of the collagen molecules of dentine or bone are present as electrostatic linkages of the form protein-COO-+H3N-protein.

Animals↗
PubMedDate not supplied

In vivo evaluation of a new type I collagen hemostatic plug for high-risk, large-core biopsies.

PURPOSE: To evaluate in a swine model the hemostatic properties of a new, expansile type I collagen plug for use in high-risk renal biopsies. MATERIALS AND METHODS: Highly purified bovine type I collagen was formed into porous cylindrical plugs and compressed radially to fit into a 5-F delivery system. On hydration these collagen plugs demonstrated radial expansion with approximately 1,600% volumetric expansion ratio. Direct exposure of both kidneys was performed in a 25-kg swine, and a bolus of 3,000 U of heparin was administered to create a coagulopathic state. A 14-gauge Temno coaxial biopsy gun was utilized in performing nine pairs of renal biopsies. The first biopsy of each biopsy pair represented the control biopsy (without collagen plug placement), whereas the second biopsy of each pair represented the plugged biopsy. The presence and duration of hemorrhage from each biopsy site was monitored visually. RESULTS: The biopsy sites without collagen plug showed immediate hemorrhage in nine of nine cases (100%), and in two of nine cases (22%) pulsatile bleeding was noted. With the use of the collagen plug, seven of nine (78%) sites showed immediate hemorrhage, but in no case was pulsatile bleeding noted. Mean bleeding duration was 156 seconds for the control biopsies versus 73 seconds for the biopsy sites plugged with collagen (P = .03, Mann-Whitney rank sum test). Bleeding duration was less than 1 minute in only one of nine (11%) control biopsies compared to six of nine (67%) collagen plug biopsies. CONCLUSIONS: A recently developed, expansile collagen hemostatic plug significantly decreases the duration of hemorrhage at renal biopsy sites in an anticoagulated swine model.

Animals↗
PubMedDate not supplied

Quantitative analysis of technetium 99m 2-methoxyisobutyl isonitrile single-photon emission computed tomography and isosorbide dinitrate infusion in assessment of myocardial viability before and after revascularization.

BACKGROUND: Assessment of viable myocardium in territories of hypoperfused myocardium is important for predicting functional recovery after revascularization. This study was designed to evaluate quantitative analysis of 99mTc-labeled 2-methoxyisobutyl isonitrile (MIBI) myocardial perfusion imaging combined with isosorbide dinitrate (ISDN) infusion to detect myocardial viability in patients with chronic coronary artery disease before and after revascularization. METHODS AND RESULTS: Twenty-seven consecutive patients with previous myocardial infarction and left ventricular dysfunction (left ventricular ejection fraction 35.2% +/- 13.5%) referred for coronary artery bypass (CABG) were studied with 99mTc-labeled MIBI single-photon emission computed tomography at rest and during ISDN infusion before CABG followed by resting imaging after CABG. Quantitative analysis was performed with circumferential profiles. Left ventricular function (global and regional) was assessed by radionuclide ventriculography before and after CABG. Out of 212 abnormal perfusion segments with resting 99mTc-labeled MIBI SPECT, 99 segments (47%) showed improved uptake of 99mTc-labeled MIBI during ISDN infusion. The mean ratio of myocardial uptake was 0.58 +/- 0.25 (resting 0.53 +/- 0.23; p < 0.05). After CABG, of 212 segments with hypoperfusion, 108 segments (51%; p > 0.05 vs ISDN) showed improved uptake of 99mTc-labeled MIBI. The mean ratio of myocardial uptake was 0.60 +/- 0.26 (resting 0.53 +/- 0.23; p < 0.05). The concordance between the improvement of post-CABG wall motion and that of pre-CABG ISDN perfusion imaging was 83%, between the improvement of wall motion and perfusion imaging after CABG 94%, and between the improvement of pre-CABG ISDN and post-CABG perfusion imaging 83%, respectively. CONCLUSION: ISDN infusion can improve the uptake of 99mTc-labeled MIBI in hypoperfused myocardium and increase the efficiency of 99mTc-labeled MIBI in the detection of viable myocardium in patients with previous myocardial infarction and left ventricular dysfunction.

Coronary Artery Bypass↗