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F Y Liu

Publications and source records attributed to F Y Liu.

At least 55 records · Page 3Linked to original sources
PubMed1991

Insulin aggregation in aqueous media and its effect on alpha-chymotrypsin-mediated proteolytic degradation.

Self-association of zinc-insulin monomers into dimers and hexamers may lead to enhanced protection of the peptide from proteolytic degradation. The present study has been undertaken to investigate the relationship, if any, between the rate of enzymatic degradation of insulin by a protease, alpha-chymotrypsin, and the extent of insulin aggregation in aqueous solutions. Insulin solutions (0.6 mg/ml) containing varying proportions of dimer and hexamer were obtained by adding ethylene diamine tetraacetic acid (EDTA) within a concentration range of 0.005 to 0.040 mM. As the EDTA concentration was increased above 0.040 mM, a complete dissociation of hexamers to dimers occurred and the rate of enzymatic degradation reached its maximum. The overall first-order rate constants appeared to be linearly related to the square of EDTA concentrations. The apparent first-order rate constants for dimer and hexamer degradation obtained from a linear plot of rate constant versus EDTA squared concentration were found to be 0.02800 +/- 0.00065 and 0.00798 +/- 0.00075 min-1, respectively. Two major insulin degradation products were also detected and the kinetics of product appearance agreed well with the disappearance kinetics of insulin. The results indicated that the degradation of insulin dimers by alpha-chymotrypsin is about 3.5 times faster than the degradation of the hexamer. The second-order dependency of degradation rate on EDTA concentration might be due to the fact that insulin hexamers contain two zinc ions which are sequestered by two EDTA molecules. Chelation of zinc ions by EDTA lead to hexamer deaggregation to dimers as was evidenced from a circular dichroism study.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effects of DuP 753 on proximal nephron and renal transport.

We used the nonpeptide angiotensin II receptor antagonist DuP 753, which lacks the agonist and kinin/prostaglandin-inducing properties of saralasin and captopril, respectively, to examine the role of endogenous angiotensin II in regulating transport in the proximal convoluted tubule (PCT) and whole kidney. During in vivo microperfusion in the Munich-Wistar rat, a maximally effective dose of DuP 753 (10 mg/kg, intravenously) powerfully inhibited absorption of bicarbonate (370 +/- 3 to 200 +/- 9 pEq/mm.min, P less than .001), chloride (214 +/- 3 to 105 +/- 9 pEq/mm.min, P less than .001), and water 5.2 +/- 0.1 to 2.8 +/- 0.2 nL/mm.min, P less than .001) in the S1 subsegment of the PCT. DuP 753 was significantly more effective than captopril (3 mg/kg, intravenously) in inhibiting sodium chloride transport and is the most potent diuretic ever described in this segment. Consistent with the axial decline of angiotensin II receptor density in the PCT, DuP 753 was a less effective transport inhibitor in the S2 subsegment of the PCT, similar to captopril. Using free-flow micropuncture and clearance techniques, though inhibition in the earliest segment of the nephron is partially compensated by downstream reabsorption, DuP 753 induces a substantial diuresis, natriuresis, and chloruresis. In conclusion, DuP 753 markedly decreases S1 PCT fluid and electrolyte absorption, indicating that endogenous angiotensin II exerts significant tonic support of proximal transport in vivo.

Angiotensin II↗
PubMed1991

The promoter, transcriptional unit, and coding sequence of herpes simplex virus 1 family 35 proteins are contained within and in frame with the UL26 open reading frame.

The herpes simplex virus 1 (HSV-1) genome specifies an abundant capsid protein which in denaturing gels forms multiple bands designated family 35 proteins (D.K. Braun, B. Roizman, and L. Pereira, J. Virol. 49:142-153, 1984). Nucleotide-sequencing studies have assigned the coding sequences of these proteins to the open reading frame UL26 (D.J. McGeoch, M.A. Dalrymple, A.J. Davidson, A. Dolan, M.C. Frame, D. McNab, L.J. Perry, J.E. Scott, and P. Taylor, J. Gen. Virol. 69:1531-1574, 1988). IN studies reported here, a series of plasmid constructs containing deletions or insertions of an alpha 4 promoter or of a sequence encoding a cytomegalovirus epitope reacting with a mouse monoclonal antibody revealed the following: the open reading frame previously designated UL26 encodes two proteins which share amino acid sequences, and each coding domain is contained in its own transcriptional unit that terminates at a common, unique poly(A) site. On the basis of the transcription initiation site (+1), it was predicted that the UL26 open reading frame encodes a protein of 635 amino acids, and a protein with an apparent molecular weight of approximately 75,000 has been identified. The second transcriptional unit, designated UL26.5, predicted to specify a protein of 329 amino acids, encodes the family 35 proteins; it is transcribed by an mRNA which initiates at approximately nucleotide +1000 of the UL26 transcription initiation site and is translated from the methionine initiation codon located at position +1099 of the UL26 transcriptional unit. The DNA fragment comprising the sequences downstream of the HpaI cleavage site (+832 of UL26) contains both the promoter and the coding sequence of family 35 proteins and is both competent and efficient in expressing the proteins in transfected cells superinfected with HSV-1 or HSV-2.

Animals↗
PubMed1991

The herpes simplex virus 1 gene encoding a protease also contains within its coding domain the gene encoding the more abundant substrate.

The herpes simplex virus 1 open reading frames UL26 and UL26.5 are 3' coterminal. The larger, UL26 open reading frame encodes a protein approximately 80,000 in apparent molecular weight and contains the promoter and coding sequence of the UL26.5 gene, which specifies a capsid protein designated infected cell protein 35. The larger product contains in its entirety the amino acid sequence of the smaller protein. We report that the UL26 gene encodes a protease which catalyzes its own cleavage and that of the more abundant product of UL26.5. By inserting the coding sequence of an epitope to a cytomegalovirus monoclonal antibody and homologs of the immunoglobulin G binding domain of staphylococcal protein A into the 3' termini of the coding domains of the two open reading frames, we identified both products of the cleavage and determined that the cleavage site is approximately 20 amino acids from the carboxyl termini of both proteins.

Animals↗
PubMed1991

Comparison of inhibitory potency by nonpeptide angiotensin II receptor antagonists PD123177 and DuP 753 on proximal nephron and renal transport.

The nonpeptide angiotensin II receptor antagonists, DuP 753 and PD123177, have been recently proposed to efficiently discriminate between two receptor subtypes. Because angiotensin II uses two signaling systems to control transport in the proximal tubule, the hypothesis was entertained that angiotensin-regulated proximal reabsorption might be transduced through two receptor subtypes and, therefore, have two components, sensitive to either DuP 753 or PD123177. Using in vivo microperfusion in the rat, a maximally effective dose of PD123177 (60 or 120 mg/kg, i.v.) had a powerful inhibitory effect on transport in the S1 proximal tubule, significantly (P less than .001) reducing bicarbonate absorption by 50% (360 +/- 4 to 179 +/- 8 peq/mm.min), chloride absorption by 38% (211 +/- 1 to 131 +/- 4 peq/mm.min) and sodium and water absorption by 32% (5.7 +/- 0.1 to 3.9 +/- 0.5 nl/mm.min). These results were only slightly different than previously reported effects on proximal solute and water absorption by DuP 753 (10 mg/kg). The two drugs demonstrated virtually no additivity in their transport inhibitory effects. Although downstream reabsorptive elements compensate for the powerful action of PD123177 in the earliest segment of the nephron, we also showed, using free-flow micropuncture and clearance techniques, that PD123177 induces a substantial diuresis, natriuresis and chloruresis, again similar in magnitude to DuP 753. These results suggest PD123177 has diuretic potency roughly equivalent to that of DuP 753, but do not lend support to the simple thesis that there are two separately acting receptor-signal transduction systems in the proximal tubule for angiotensin II.

Angiotensin II↗
PubMed1990

Adenosine triphosphate liposomes: encapsulation and distribution studies.

Four methods for encapsulating adenosine triphosphate (ATP) in liposomes were evaluated. Optimum entrapment required emulsifying ATP with the lipids used to form the liposome membrane in a high-speed homogenizer followed by evaporating the organic solvent with vigorous stirring. Under these optimum conditions ATP entrapment was 38.9%; i.e., the dosage form contained 38.9 g of ATP per 100 g of lipid. The distribution of positively charged liposomes loaded with ATP was studied in dogs with experimentally induced myocardial infarction. Intravenous injection of positively charged ATP liposomes caused accumulation of ATP in myocardial infarct tissue. Myocardial infarct tissue has reduced blood flow; since positively charged liposomes accumulated in infarct tissue, liposomes may be a drug delivery system for this disease state.

Adenosine Triphosphate↗
PubMed1990

Beta-cyclodextrin/steroid complexation: effect of steroid structure on association equilibria.

Molecular associations of beta-cyclodextrin (beta-CyD) with four steroids (cortisone, hydrocortisone, progesterone, and testosterone) have been studied using phase-solubility and spectroscopic techniques. Phase solubility diagrams could be categorized as B type. The complexes are formed at the stoichiometric ratios of 1:2 (drug:beta-CyD). A mathematical model has been proposed to calculate the apparent stability constants. The results suggest that the inclusion of a steroid molecule into the first beta-CyD cavity is thermodynamically more favorable over the association of 1:1 complex with the second beta-CyD molecule except for cortisone, which exhibits anomalous behavior. A mechanism of complexation has been proposed based on the apparent stability constants and chemical structures of the steroids and beta-CyD. It suggests that complexation is first brought about by inclusion of the five-member cyclopentane ring of the steroid molecule into the first beta-CyD cavity. The 1:1 complex subsequently binds with the second beta-CyD to form the 1:2 complex. The association constants of steroid/beta-CyD complexes are of the following order: progesterone greater than cortisone greater than testosterone greater than hydrocortisone. The order of aqueous solubilities of the complexes is hydrocortisone greater than cortisone greater than testosterone greater than progesterone.

Cortisone↗
PubMed1990

Proximal nephron and renal effects of DuP 753, a nonpeptide angiotensin II receptor antagonist.

The purpose of these studies was to quantitatively assess the role of endogenous angiotensin II activity in controlling transport in the proximal convoluted tubule (PCT) and whole nephron. We used the nonpeptide angiotensin II receptor antagonist DuP 753, which lacks the agonist and kinin/prostaglandin-inducing properties of saralasin and captopril, respectively. During in vivo microperfusion in the Munich-Wistar rat, we found that DuP 753 had a powerful inhibitory effect on bicarbonate (370 +/- 3 to 200 +/- 9 pEq/mm.min, P less than 0.001), chloride (214 +/- 3 to 105 +/- 9 pEq/mm.min, P less than 0.001), and water (5.2 +/- 0.1 to 2.8 +/- 0.2 nl/mm.min, P less than 0.001) absorption in the S1 subsegment of the PCT. At maximally effective doses, DuP 753 (10 mg/kg i.v.) was significantly more effective than was captopril (3 mg/kg i.v.) in inhibiting sodium chloride transport in the S1 PCT. DuP 753 is the most potent diuretic ever described in this segment. Consistent with the axial decline of angiotensin II receptor density in the PCT, DuP 753 was a less effective transport inhibitor in the S2 subsegment of the PCT, similar to captopril. Though downstream reabsorptive elements partially compensate for the action in the earliest segment of the nephron, we also showed using free-flow micropuncture and clearance techniques that DuP 753 induces a substantial diuresis, natriuresis and chloruresis. In conclusion, the marked decrease in S1 PCT fluid and electrolyte absorption induced by DuP 753 indicates that endogenous angiotensin II exerts significant tonic support of proximal transport in vivo.

Angiotensin II↗
PubMed1990

A new approach to the modeling and control of postoperative pain.

The objective of this paper has been to explore contributions which the technology of control engineering can make to the relief of postoperative pain. A human-operated, closed-loop, analgesic drug injection system has been designed to alleviate chronic pain. In this system, a patient presses a button when pain relief is required. A computer interfaces the button to the patient's drug injection pump. A patient pain model has been developed to describe the dynamics of the human physiological and psychological responses to chronic pain. A pharmacokinetic model of analgesia is also included. The pain model has been validated by adjusting its parameters so that its behavior mimics actual button-pressing records of self-administered analgesia. A modified Smith delay compensator and IPFM controller are used to compensate for the inherent nonlinearity of the system and to obtain the high performance required. The results of this simulation study are promising. The nonlinear patient pain model represents a contribution to the description of the dynamics and quantification of pain. The control algorithms proposed have shown, through modeling studies, an improvement in the performance of self-administered analgesia systems. The simulated patients obtained good pain relief without excessive button-pressing, and without undesirable high concentrations of opioids being observed. The SDC/IPFM controller architecture has been found to be robust in the presence of pain noise and pharmacokinetic plant parameter changes.

Analgesia, Patient-Controlled↗
PubMed1990

Role of protein kinase C in proximal bicarbonate absorption and angiotensin signaling.

Using in vivo microperfusion in the proximal convoluted tubule (PCT) of the Munich-Wistar rat, we investigated the impact of varying protein kinase C (PKC) activity on the rate of bicarbonate reabsorption and on its regulation by angiotensin II. Activation of PKC with luminal perfusion of phorbol 12-myristate 13-acetate (PMA, 5 x 10(-7) M) caused bicarbonate absorption in the S1 PCT to increase by 25%, from 346 +/- 7 to 432 +/- 4 peq.mm-1.min-1 (P less than 0.001), without affecting intracellular cAMP level. Another PKC stimulator, dioctanoylglycerol, had the same effect. Inhibition of PKC activity with luminal perfusion of 5 x 10(-6) M sphingosine had the opposite effect, decreasing bicarbonate absorption by 45% to 190 +/- 2 peq.mm-1.min-1 (P less than 0.001). Pretreatment with PMA or with sphingosine each attenuated by approximately one-third the bicarbonate absorptive response usually observed following angiotensin II administration. Similar results for the action of PKC, but of smaller magnitude, were found in the S2 PCT. In conclusion, activation of PKC increases bicarbonate and water absorption in the S1 and S2 PCT in vivo, and PKC may participate in as much as one-third of the transport stimulation induced by angiotensin II.

Absorption↗
PubMed1990

Role of angiotensin II in glomerulotubular balance.

Inhibition of angiotensin II activity reduces reabsorption of both bicarbonate and chloride predominantly in the S1 subsegment of the proximal convoluted tubule (PCT). Because the S2 PCT is intrinsically better able to compensate for the increased delivery of bicarbonate compared with chloride under normal conditions, we reasoned that angiotensin II inhibition might selectively raise the amount of sodium chloride emerging from the PCT. Free-flow micropuncture techniques were used in normal and alkalotic Munich-Wistar rats that were euvolemic or plasma volume depleted. In the normal volume-depleted animals, saralasin caused a small rise in single-nephron glomerular filtration rate (29.5 +/- 0.6 to 31.5 +/- 0.6 nl/min, P less than 0.025) and fall in bicarbonate and chloride reabsorption in the 1st mm (S1) PCT (387 +/- 22 to 348 +/- 23 peq.mm-1.min-1, P less than 0.05, and 341 +/- 27 to 217 +/- 57 peq.mm-1.min-1, P less than 0.05, respectively). Reabsorptive compensation by the S2 PCT maintained the end-PCT delivery of bicarbonate unchanged (76 +/- 4 to 78 +/- 3 peq.mm-1.min-1, NS), but end-PCT chloride delivery increased significantly (2,014 +/- 41 to 2,248 +/- 29 peq.mm-1.min-1, P less than 0.01). Early distal convoluted tubule (DCT) and urinary bicarbonate excretion were unchanged, but DCT chloride delivery increased associated with a chloruresis. When metabolic alkalosis was present, however, S2 compensation for increased bicarbonate delivery was attenuated so that end-PCT, DCT, and urinary bicarbonate as well as chloride delivery rates increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkalosis↗
PubMed1990

Effects of intracellular calcium on proximal bicarbonate absorption.

Using in vivo microperfusion in the proximal convoluted tubule (PCT) of the Munich-Wistar rat, we assessed the impact of raising intracellular calcium concentration on bicarbonate transport and its regulation by angiotensin II. Luminal perfusion with the calcium ionophore A23187 caused a dose-dependent increase in S1 PCT bicarbonate absorption, with a maximal change of 60 peq.mm-1.min-1. Subsequent addition of phorbol ester (PMA) after A23187 further increased transport but to a level no higher than previously shown with PMA alone, and A23187 was nonstimulatory when added after PMA. These results suggest that intracellular calcium affects the same pathway as protein kinase C in stimulating proximal acidification. Pretreatment with A23187 (+/- PMA) attenuated by approximately one-third the bicarbonate absorptive response in the S1 PCT usually observed after angiotensin II administration. A23187 had similar actions, but of smaller magnitude, in the S2 PCT. In conclusion, a rise in intracellular calcium increases bicarbonate absorption in the S1 and S2 PCT in vivo.

Absorption↗
PubMed1989

Angiotensin II stimulates early proximal bicarbonate absorption in the rat by decreasing cyclic adenosine monophosphate.

These studies explored the hypothesis that angiotensin II increases bicarbonate absorption in the proximal convoluted tubule (PCT) by decreasing intracellular cAMP. In vivo microperfusion was performed in rat PCT with measurements of bicarbonate absorption and of tubular fluid cAMP delivery, as a reflection of intracellular cAMP. Intravenous angiotensin II potently increased S1 PCT bicarbonate absorption (348 +/- 11 to 588 +/- 8 peq/min.min, P less than 0.001) and decreased tubular fluid cAMP (18 +/- 2 to 12 +/- 2 fmol/mm.min, P less than 0.05). Parathyroid hormone had the expected opposite effects, which were additive to those of angiotensin II. Over a wide range of hormonal activities, there was an excellent inverse relationship between hormonally modulated bicarbonate absorption and cAMP delivery. Pertussis toxin pretreatment significantly attenuated (by 35-45%) the angiotensin-induced increase in bicarbonate absorption and decrease in cAMP delivery, indicating Gi-protein intermediation. Luminal dibutyryl cAMP abolished the transport response to angiotensin II. In conclusion, these in vivo results suggest angiotensin II stimulates bicarbonate absorption in the S1 PCT by a G1-mediated depression in intracellular cAMP.

Adenylyl Cyclases↗
PubMed1988

Flow dependence of bicarbonate transport in the early (S1) proximal convoluted tubule.

We previously found, using an in vivo microperfusion pump rate of 30 nl/min, that proton secretion in the early (S1) proximal convoluted tubule (PCT) of the Munich-Wistar rat exhibited saturation kinetics. The maximal transport capacity was very high, approximately 500-600 peq.mm-1.min-1. The present studies assessed the change in early PCT acidification kinetics in response to an increase in microperfusion rate to 45 nl/min. First, bicarbonate permeability in the early PCT was measured and was found to be flow dependent. Proton secretion was then calculated using perfusate bicarbonate concentrations from 8 to 100 mM. Saturation of early proximal acidification (Vmax) still occurred at approximately 500-600 peq.mm-1.min-1, but the bicarbonate concentration effecting half-maximal acidification (apparent Km) decreased (from approximately 11 mM at 30 nl/min perfusion rate to less than 6 mM at 45 nl/min). By increasing luminal perfusion rate further to 60 nl/min at constant luminal bicarbonate concentration (25 mM), we confirmed that luminal flow rate did not affect the maximal level of acidification. Similar flow-dependent changes in acidification kinetics in the late PCT were also found, as has been previously shown. In conclusion, although an increase in luminal flow increased bicarbonate permeability and apparent affinity for substrate transport, there was no effect on maximal acidification rate in the early PCT.

Animals↗
PubMed1988

Atrial natriuretic factor does not inhibit basal or angiotensin II-stimulated proximal transport.

Atrial natriuretic factor (ANF) can functionally overcome the effects of angiotensin II in several tissues. Since ANF and angiotensin II in physiological concentrations have opposite effects on renal sodium excretion, we evaluated whether functional antagonism of the two hormones occurs in the proximal convoluted tubule, as has been recently reported with use of the shrinking split-droplet technique. We used the more conventional technique of in vivo microperfusion to measure the response to systemic ANF (0.5 micrograms.kg-1.min-1) when the endogenous angiotensin II level and proximal transport were normal or when transport was first stimulated by systemic angiotensin II administration (20 ng.kg-1.min-1). In both cases, ANF did not significantly alter bicarbonate, chloride, or water transport in either the early or late proximal convoluted tubule. This inability by ANF to directly affect proximal transport is consonant with the known lack of high-affinity receptors and appropriate second messenger system for ANF in the proximal convoluted tubule.

Angiotensin II↗
PubMed1988

Urinary cGMP as biological marker of the renal activity of atrial natriuretic factor.

Current evidence suggests guanosine 3',5'-cyclic monophosphate (cGMP) serves as the second messenger for atrial natriuretic factor (ANF) in the kidney in vivo. We examined whether extracellular cGMP accumulation quantitatively reflected the concentration of cGMP within renal cells and whether urinary excretion of cGMP correlated with the physiological action of ANF. cGMP egression was examined in renal epithelial LLC-PK1 cells. ANF augmented intracellular cGMP concentration and extracellular cGMP appearance. Extracellular cGMP was an excellent function of the time-integrated intracellular cGMP concentration. In clearance studies in awake rats, urinary cGMP was primarily of renal cellular origin and correlated with the natriuresis induced by ANF in a time-dependent and concentration-dependent fashion. Urinary cGMP excretion may be useful as a biological marker for the renal activity of ANF in vivo.

Animals↗
PubMed1988

Angiotensin II stimulation of hydrogen ion secretion in the rat early proximal tubule. Modes of action, mechanism, and kinetics.

Physiologic concentrations of angiotensin II stimulate sodium transport by intestinal and renal early (S1) and late (S2) proximal tubule epithelial cells. We recently found that hydrogen ion secretion, which effects sodium bicarbonate absorption, was a transport function preferentially and potently increased by angiotensin II in S1 cells. S1 cells are normally responsible for half of the total renal hydrogen ion secretion. The mechanism by which angiotensin II regulates intestinal sodium transport is by potentiating sympathetic nerve activity and norepinephrine release. Direct control of hydrogen ion secretion by angiotensin II via receptors on epithelial cells has not been previously demonstrated. We now report that stimulation of in vivo hydrogen ion secretion in the rat early proximal tubule by angiotensin II was not mediated via change in nerve activity. Rather, enhanced hydrogen ion secretion by angiotensin II correlated with increased angiotensin II receptor density on epithelial cells in the early compared to late microdissected proximal tubule. Basolateral as well as luminal angiotensin II stimulated bicarbonate absorption. Angiotensin II reduced bicarbonate permeability and caused alteration in the apparent substrate affinity, but not maximal capacity, of the proximal hydrogen ion secretory system involving the Na+/H+ antiporter.

Angiotensin II↗