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T C Williams

Publications and source records attributed to T C Williams.

At least 37 records · Page 2Linked to original sources
PubMed1990

Effects of nisoldipine on the no-reflow phenomenon in globally ischemic rat hearts.

Isolated working rat hearts, receiving no drug treatment, recovered low values of contractile function after 33 min of zero-flow global ischemia and 30-min reperfusion, had lower ATP and creatine phosphate (CrP) values in the subendocardium than in the subepicardium after reperfusion (subendocardial/subepicardial ratio ATP = 0.44, CrP = 0.45), and had a subendocardial reperfusion defect including 15.9% of ventricular cross-sectional area. Contracture pressure increased during the later part of ischemia to 25.4 mm Hg. Addition of nisoldipine (1 nM) 10 min before ischemia did not depress preischemic contractile function and did not delay or reduce contracture or the breakdown of high-energy phosphate compounds during ischemia. On reperfusion, nisoldipine-treated hearts showed a dramatic improvement in recovery of contractile function, increased subendocardial energy levels yielding a more uniform transmural energy distribution (subendocardial/subepicardial ratio ATP = 0.79, CrP = 0.94), and enhanced reflow to the subendocardium (area of no reflow = 1.0%). In contrast, addition of vehicle or a low concentration of verapamil (1 nM) before ischemia or nisoldipine during reperfusion did not improve recovery of contractile function. The beneficial effects do not appear to be induced by direct myocardial actions of nisoldipine but may reflect improved vascular function which is associated with the vascular selectivity of this calcium antagonist.

Analysis of Variance↗
PubMed1989

Characterization of sodium-dependent and sodium-independent nucleoside transport systems in rabbit brush-border and basolateral plasma-membrane vesicles from the renal outer cortex.

The transport of uridine into rabbit renal outer-cortical brush-border and basolateral membrane vesicles was compared at 22 degrees C. Uridine was taken up into an osmotically active space in the absence of metabolism for both types of membrane vesicles. Uridine influx by brush-border membrane vesicles was stimulated by Na+, and in the presence of inwardly directed gradients of Na+ a transient overshoot phenomenon was observed, indicating active transport. Kinetic analysis of the saturable Na+-dependent component of uridine flux indicated that it was consistent with Michaelis-Menten kinetics (Km 12 +/- 3 microM, Vmax. 3.9 +/- 0.9 pmol/s per mg of protein). The sodium:uridine coupling stoichiometry was found to be consistent with 1:1 and involved the net transfer of positive charge. In contrast, uridine influx by basolateral membrane vesicles was not dependent on the cation present and was inhibited by nitrobenzylthioinosine (NBMPR). NBMPR-sensitive uridine transport was saturable (Km 137 +/- 20 microM, Vmax. 5.2 +/- 0.6 pmol/s per mg of protein). Inhibition of uridine flux by NBMPR was associated with high-affinity binding of NBMPR to the basolateral membrane (Kd 0.74 +/- 0.46 nM). Binding of NBMPR to these sites was competitively blocked by adenosine and uridine. These results indicate that uridine crosses the brush-border surface of rabbit proximal renal tubule cells by Na+-dependent pathways, but permeates the basolateral surface by NBMPR-sensitive facilitated-diffusion carriers.

Animals↗
PubMed1989

Characterization and site-specific mutagenesis of the calcium-binding protein oncomodulin produced by recombinant bacteria.

A bacterial expression system for the parvalbumin-like calcium-binding protein oncomodulin has been constructed. This system can yield 50-fold more oncomodulin than the richest known mammalian source, the rat Morris hepatoma 5123. The bacterially produced protein folded correctly as monitored by UV, fluorescence, and 1H nuclear magnetic resonance spectroscopy and is immunologically identical to rat hepatoma oncomodulin. A calcium-specific conformational change is observed in the bacterial oncomodulin similar to that of the hepatoma protein. A modification of the putative calcium-specific CD loop by site-directed mutagenesis, which changed Asp-59 to Glu-59, eliminates calcium-specific effects. In contrast to the native molecule, the mutant Glu-59 now exhibits a magnesium-induced conformational change when monitored by UV difference or fluorescence excitation spectroscopy. The availability of large amounts of bacterially produced oncomodulin combined with the ability to modify at will the metal-binding ligands should now allow dissection of the unusual pairing in oncomodulin of one calcium-specific calmodulin-like site with one calcium/magnesium parvalbumin-like site.

Amino Acid Sequence↗
PubMed1988

Differential effects of somatostatin (SRIH) and a SRIH analog, SMS 201-995, on the secretion of growth hormone and thyroid-stimulating hormone in man.

We compared the ability of SRIH and SRIH analog, SMS 201-995 (SMS), to inhibit stimulated GH and TSH secretion in men who received 120-min iv infusions of saline, SRIH (5, 50, and 500 micrograms/h), and SMS (3, 30, and 300 ng/kg.h) together with a bolus iv injection of GHRH (1 microgram/kg) and TRH (500 micrograms). Integrated GH secretion during the 60 min after GHRH plus TRH injection was decreased compared to that after saline by (mean +/- SE) 32 +/- 14% (P = 0.059), 78 +/- 5% (P less than 0.001), and 88 +/- 3% (P less than 0.001) during the 5, 50, and 500 micrograms/h SRIH infusions, and by 13 +/- 7% (P = NS), 50 +/- 15% (P less than 0.05), and 80 +/- 6% (P less than 0.001) during the 3, 30, and 300 ng/kg.h SMS infusions. In contrast, integrated TSH secretion was unaltered during the 5 micrograms/h SRIH and 3 ng/kg.h SMS infusions; it decreased by only 43 +/- 5% (P less than 0.001) and 66 +/- 4% (P less than 0.001) during the 50 and 500 micrograms/h SRIH infusions and by 33 +/- 8% (P less than 0.05) and 50 +/- 3% (P less than 0.001) during the 30 and 300 ng/kg.h SMS infusions. Analysis of the dose-response curves indicated approximately 10- and 5-fold greater potencies of SRIH and SMS, respectively, in inhibiting GH as compared to TSH secretion. These results quantify the effect of SRIH as an inhibitor of GH secretion and suggest that if SRIH has a physiological role in the inhibition of TSH secretion in man, it is limited to conditions associated with marked suppression of GH.

Adult↗
PubMed1988

Comparison of the sensitivity of growth hormone secretion to somatostatin in vivo and in vitro in acromegaly.

Somatostatin (SRIH) sensitivity in acromegaly was evaluated in vivo by comparing the inhibition of GHRH (1 microgram/kg, iv)-stimulated GH secretion in eight acromegalic and six normal subjects. A SRIH infusion (50 micrograms/h) that inhibited the mean plasma GH response to GHRH by 74 +/- 5% (+/- SE) in normal subjects had no significant effect in the acromegalic patients. However, when two acromegalic patients in whom SRIH had no suppressive effect were excluded from the analysis, the effect of SRIH in the other six (82 +/- 7%) was comparable to that in the normal subjects. Within the acromegalic group, the percent suppression of basal and GHRH-stimulated GH secretion was inversely correlated with both basal plasma GH (r = -0.751; P = 0.03 and r = -0.727; P = 0.04, respectively) and insulin-like growth factor I (r = -0.800; P = 0.02 and r = -0.727; P = 0.04, respectively) concentrations. The in vitro sensitivity to SRIH was studied in pituitary adenomas from five of the acromegalic patients in 3- to 4-day monolayer cultures of dispersed cells. The SRIH IC50 values were lowest in the tumors (8.6-44 pmol/L) from the three patients who had in vivo SRIH sensitivity (suppression of GHRH-stimulated GH secretion) comparable to that in the normal subjects. The IC50 values were higher in the tumors (150 and 21,000 pmol/L) from the two patients that were least responsive to SRIH in vivo. These results indicate that there is considerable variability of SRIH sensitivity in patients with acromegaly. Although the role of this defect in the pathogenesis of acromegaly is uncertain, it may be an important determinant in the degree of elevation of plasma GH levels.

Acromegaly↗
PubMed1987

Oncomodulin. 1H NMR and optical stopped-flow spectroscopic studies of its solution conformation and metal-binding properties.

As deduced from its 1H NMR spectrum, oncomodulin's solution conformation is very similar to the tertiary structure of other single domain 2-site calcium-binding proteins of the troponin C class. Despite its extensive amino acid sequence homology with parvalbumins, however, oncomodulin differs significantly from these proteins in its Ca(II)----Ln(III) exchange characteristics. Although the relative affinity of Lu(III) for the EF site of Ca2-oncomodulin was normal, beta Lu:EF/beta Ca:EF being 175 +/- 15, displacement of Ca(II) from the CD site was not favored, beta Lu:CD/beta Ca:CD being 1.2 +/- 0.1. Lineshape analyses of several 1H NMR resonances generated by the Lu(III) titration of Ca2-oncomodulin indicated that Ca(II)----Ln(III) exchange at the CD site was 15-20 s-1, approximately 100 times faster than exchange at the CD site of parvalbumins. Analyses of the distribution of metal-bound oncomodulin species showed that Ca(II)----Lu(III) exchange was cooperative, the coefficient of cooperativity being estimated as 5 +/- 1. The kinetics of the release of Yb(III) from oncomodulin as measured by optical stopped-flow techniques corroborated the observed cooperativity in metal binding; the off-rate constant of Yb(III) from the EF site of Yb2-oncomodulin was 0.0036 s-1, approximately 19 times slower than the release of Yb(III) from the EF site of Ca1Yb1-oncomodulin. We attribute part of the reduced preference of small Ln(III)s for the CD site of oncomodulin to a combination of this site's inherent incompressibility (Williams, T.C., Corson, D.C. & Sykes, B.D. (1984) J. Am. Chem. Soc. 106, 5698-5702) and the Glu----Asp substitution at sequence position 59, the residue which chelates metal at the -X coordination position. Like the CD site in oncomodulin, site III in troponin C has not only a lower affinity for calcium relative to the CD site of parvalbumins but also aspartic acid at its -X position; a water molecule bridges the gap between bound metal and the carboxyl group of the relatively short side chain of Asp-114 (Herzberg, O. & James, M. N. G. (1985) Biochemistry 24, 5298-5302). Hence, we suggest that Asp-59 in oncomodulin binds metal only indirectly through an intervening water molecule, a proposal which is consistent with the CD site's reduced affinity for ions the size of Ca(II) or smaller.

Animals↗
PubMed1987

Intravenous medroxalol stimulates prolactin secretion in normal and hypertensive subjects.

This study evaluated the effects of medroxalol on prolactin secretion. Twelve normal subjects received medroxalol, 1 mg/kg, intravenously and on a separate occasion, 5% dextrose in water. Integrated prolactin secretion during the 3 hours after medroxalol injection was significantly increased as compared with dextrose (P less than 0.001). Intravenous administration of medroxalol, 2 mg/kg, to 10 hypertensive subjects resulted in significant elevation of mean prolactin levels above basal levels at all time intervals measured from 30 to 240 minutes after injection. Oral medroxalol administration to 11 hypertensive subjects for up to 15 months did not alter mean prolactin levels. Medroxalol neither stimulated prolactin release nor decreased dopamine suppression of prolactin release from pituitary cell cultures. In conclusion, intravenous medroxalol stimulates prolactin secretion in both normal and hypertensive subjects. This effect is not likely mediated by a direct action of the drug on the pituitary but rather by an effect either within the central nervous system or of a drug metabolite.

Adult↗
PubMed1986

1H NMR spectroscopic studies of calcium-binding proteins. 1. Stepwise proteolysis of the C-terminal alpha-helix of a helix-loop-helix metal-binding domain.

A series of modified parvalbumins, differing only in length of alpha-helix F at the C-terminus, was prepared by carboxypeptidase-mediated digestions of the beta-lineage parvalbumin (pI = 4.25) from carp (N; 108 residues). Removal of Ala-108 to form the N-1 derivative (des-Ala108,Lys107-parvalbumin) only slightly alters the protein's ability to chelate Ca(II) or lanthanides(III). Analysis of the kinetics of their Yb(III) off-rates by optical stopped-flow techniques, determination of their Lu(III)-binding constants by high-resolution 1H NMR methods, and inspection of their solution structures by Yb(III)-shifted 1H NMR techniques indicate N-1 and N-2 are very similar to N (0.1-0.2 M KCl; pH 6-7; 23-55 degrees C). However, removal of the next one or two residues, Val-106 or Val-106/Leu-105, to generate the N-3 and N-4 derivatives severely alters the metal ion binding characteristics of the protein. Although two Yb(III) off-rates are observed for N-3, both are faster than that for the unmodified protein: kCD by a factor of 2 and kEF by a factor of 2200. Removal of Ala-104 and Ala-104/Thr-103 to give a mixture of N-5 and N-6 derivatives eliminates the slow-release site altogether, the single observable koff being 20-30 times faster than release of Yb(III) from the CD site of native parvalbumin. Removal of the C-terminal alpha-helix by digestion through Phe-102 to give N-7 destabilizes the entire protein structure as judged both by the random-coil appearance of its 1H NMR spectrum and by its aberrant kinetics. Although one abnormally fast koff is still observed at micromolar concentrations, Ln(III) chelation tends to precipitate N-7 at higher parvalbumin concentrations (1-3 mM). In contrast to the critical instability of the N-3 through N-7 derivatives, the remarkable stability of the N-1 and N-2 forms of carp parvalbumin may be attributed to the maintainance of two key structural features: an ion pair bond between the negatively charged C-terminal carboxyl function and the protonated epsilon-NH3+ of Lys-27 and hydrophobic interactions of the inner side of helix F with residues in the protein's core.

Animals↗
PubMed1986

1H NMR spectroscopic studies of calcium-binding proteins. 2. Histidine microenvironments in alpha- and beta-parvalbumins as determined by protonation and laser photochemically induced dynamic nuclear polarization effects.

The microenvironments of the histidines in three isoforms of Ca(II)-bound parvalbumin (carp, pI = 4.25; pike, pI = 5.00; rat, pI = 5.50) have been examined with 1H NMR techniques to probe their protonation characteristics and photochemically induced dynamic nuclear polarizability (photo-CIDNP). The histidine at position 26 (or 25), present in all three of these proteins, shows absolutely no photo-CIDNP enhancement of its C2H or C5H resonances. Nor does this nonpolarizable histidine possess a normal pKa: values range only from 4.20 for carp to 4.32 for pike to 4.44 for rat. The C2H and C5H resonances of the histidine in this carp isoform split into doublets as the pH is lowered. The magnitude of this splitting depends on the magnetic field strength, temperature, and pH; however, the line intensities within each doublet are temperature-independent. Although the crystal structure of carp parvalbumin indicates that His-26 is exposed to solvent [Kretsinger, R. H., & Nockolds, C. E. (1973) J. Biol. Chem. 248, 3313-3326], we conclude that in solution this residue, in its unprotonated state, is part of the hydrophobic core of the protein. In contrast, His-48 in rat parvalbumin and His-106 in pike III parvalbumin show dramatic photo-CIDNP enhancements of their C2H, C5H, and beta-CH2 1H NMR resonances. Combined with its nearly normal pKa, 6.14, and exchange-broadened C2H resonance, the photo-CIDNP enhancement results for His-48 indicate that its microenvironment differs little from random-coil exposure, consistent with its presumed position on the solvent surface of helix C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

1H NMR spectroscopic studies of calcium-binding proteins. 3. Solution conformations of rat apo-alpha-parvalbumin and metal-bound rat alpha-parvalbumin.

Lacking the extraordinary thermal stability of its metal-bound forms, apo-alpha-parvalbumin from rat muscle assumes two distinct conformations in aqueous solution. At 25 degrees C, its highly structured form predominates (Keq = 5.7; delta G degree = -4.3 kJ X mol-1); as deduced from both 1H NMR and circular dichroism (CD) spectroscopy, this conformation is exceedingly similar to those of its Mg(II)-, Ca(II)-, and Lu(III)-bound forms. The temperature dependences of several well-resolved aromatic and upfield-shifted methyl 1H NMR resonances and several CD bands indicate that the native, highly helical structure of rat apo-alpha-parvalbumin is unfolded by a concerted mechanism, showing no indication of partially structured intermediates. The melting temperature, TM, of rat apo-alpha-parvalbumin is 35 +/- 0.5 degrees C as calculated by both spectroscopic techniques. By 45 degrees C, rat apo-alpha-parvalbumin unfolds entirely, losing the tertiary structure that characterizes its folded form: not only are the ring-current-shifted aromatic and methyl 1H NMR resonances leveled, but the 262- and 269-nm CD bands are also severely reduced. As judged by the decrease in the negative ellipticity of the 222-nm CD band, this less-structured form of rat apo-alpha-parvalbumin shows an approximate 50% loss in apparent alpha-helical content compared to its folded state. Several changes in the 1H NMR spectrum of rat apo-alpha-parvalbumin were exceptionally informative probes of the specific conformational changes that accompany metal ion binding and metal ion exchange. In particular, the line intensities of the ortho proton resonance of Phe-47, the unassigned downfield-shifted alpha-CH resonances from the beta-sheet contacts between the metal-binding loops, the C2H resonance of His-48, and the epsilon-CH3 resonance of an unassigned Met residue were monitored as a function of added metal to determine the stability constants of several metal ion-parvalbumin complexes. We conclude that Mg(II) binds to the CD and EF sites independently, its affinity for the EF site being almost twice that for the CD site. Mg(II)----Ca(II) exchange showed that the CD-site Mg(II) is displaced first, in contrast to Lu(III)'s preferential displacement of the EF-site Ca(II) as determined from the Ca(II)----Lu(III) exchange experiments.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

Rapid enzymatic degradation of growth hormone-releasing hormone by plasma in vitro and in vivo to a biologically inactive product cleaved at the NH2 terminus.

The effect of plasma on degradation of human growth hormone-releasing hormone (GRH) was examined in vitro and in vivo using high performance liquid chromatography (HPLC), radioimmunoassay (RIA), and bioassay. When GRH(1-44)-NH2 was incubated with human plasma, the t1/2 of total GRH immunoreactivity was 63 min (RIA). However, HPLC revealed a more rapid disappearance (t1/2, 17 min) of GRH(1-44)-NH2 that was associated with the appearance of a less hydrophobic but relatively stable peptide that was fully immunoreactive. Sequence analysis indicated its structure to be GRH(3-44)-NH2. Identity was also confirmed by co-elution of purified and synthetic peptides on HPLC. Biologic activity of GRH(3-44)-NH2 was less than 10(-3) that of GRH(1-44)-NH2. After intravenous injection of GRH(1-44)-NH2 in normal subjects, a plasma immunoreactive peak with HPLC retention comparable to GRH(3-44)-NH2 was detected within 1 min and the t1/2 of GRH(1-44)-NH2 (HPLC) was 6.8 min. The results provide evidence for GRH inactivation by a plasma dipeptidylaminopeptidase that could limit its effect on the pituitary.

Adult↗
PubMed1985

Tetrahydrobiopterin analogues: solution conformations of 6-methyltetrahydropterin, 7-methyltetrahydropterin, and cis- and trans-6,7-dimethyltetrahydropterins as determined by proton nuclear magnetic resonance.

The conformation of tetrahydrobiopterin analogues in aqueous solution at 23 degrees C has been determined by analyzing the 200-MHz 1H NMR spectral parameters of the enzymatically active 6-methyltetrahydropterin, 7-methyltetrahydropterin, and cis- and trans-6,7-dimethyl-5,6,7,8-tetrahydropterins. Each of these cofactors, with the exception of the cis-6,7-dimethyl isomer, exhibited an unusually small trans 6H-7H spin-spin coupling (8.5-9.1 Hz). An empirical equation that accounts for the effects of substituent electronegativity and orientation on vicinal couplings [Haasnoot, C. A. G., deLeeuw, F. A. A. M., & Altona, C. (1980) Tetrahedron 36, 2783-2792] predicted this coupling to be 11.3-11.6 Hz. We attribute the discrepancy between the calculated and experimentally observed values of this coupling to hyperconjugation of the axially oriented C7-H bond with the pi orbital of the vinylogous amide protein of the pterin ring (N8-C8a = C4a-C4 = O) rather than conformational averaging. The trans 6H-7H interproton distance in the 6-methyl analogue is calculated to be 3.0 A from the measured decrease in the spin-lattice relaxation rate of the axially oriented C7 proton after specific deuteration at C6. This is consistent with the single-conformer interpretation. Chemical shift comparisons of the methyl resonances of these analogues, NOE measurements from selectively deuterated analogues, and the differential sensitivities of axially vs. equatorially disposed ring protons to protonation at N5 all indicate that (i) the methyl substituents at both the C6 and C7 positions markedly prefer equatorial-like orientations and (ii) the tetrahydropterin ring is, with the exception of a pronounced pucker at C6, nearly planar.(ABSTRACT TRUNCATED AT 250 WORDS)

Biopterins↗
PubMed1985

Bar codes and their potential applications in hospital pharmacy.

The technology and terminology of bar codes, the Health Industry Bar Code (HIBC) Standard, issues facing the pharmaceutical industry with respect to bar codes, and potential applications of bar codes in hospital pharmacy are reviewed. Bar codes consist of a series of parallel alternating dark lines and empty spaces. Commonly used bar codes include UPC (Universal Product Code), Interleaved 2 of 5, Codabar, Code 93, Code 128, and Code 39. There are several different types of scanners that may be used for scanning bar codes. Some of the variable features are portability, contact and noncontact, autodiscrimination, and the presence of numeric keypads. The HIBC Council (HIBCC) is a steering committee charged with developing bar-code standards for health care, assigning identification numbers to manufacturers, and providing information to interested individuals. The HIBCC Board includes representatives from health-care providers, equipment manufacturers, drug manufacturers, and wholesalers. Drug manufacturers are concerned about several issues with regard to bar codes; for example, who will pay for the cost of implementation, on what level of packaging will the bar codes be required, and are there legal implications if a poor scan results in patient harm? Bar codes have already been applied in some hospitals for coding blood containers, roentgenogram jackets, medical records, and capital equipment. The potential applications in hospital pharmacy include inventory control, verifying the accuracy of dispensing to both inpatients and outpatients, and record keeping for drug product expiration or disposal. Bar codes also offer pharmacists the ability to perform in-process dispensing controls that are not practical to perform manually. Bar-code technology offers health-care personnel the opportunity to improve work efficiency and increase the accuracy of data entry into automated systems.

Computers↗
PubMed1983

Calcium binding proteins: optical stopped-flow and proton nuclear magnetic resonance studies of the binding of the lanthanide series of metal ions to parvalbumin.

Optical stopped-flow techniques have been used to determine the dissociation rate constants (koff) for the lanthanide(III) ions from carp (pI 4.25) parvalbumin. For most of the 13 different lanthanides studied, the release kinetics were diphasic, composed of both a fast phase (whose rate varied across the series, La3+ leads to Lu3+, between the limits -1.2 less than or equal to log kFAST less than or equal to -0.7) and a slower phase (whose rate varied across the series, La3+ leads to Lu3+, between the limits -1.2 greater than or equal to log kSLOW greater than or equal to -2.9). In addition, the La3+- and Lu3+-induced changes in the 270-MHz proton nuclear magnetic resonance spectrum of parvalbumin were used to calculate the dissociation constants for these specific lanthanides from the two high-affinity Ca2+ binding sites. The KD for one site appears to remain constant across the lanthanide series, determined to be 4.8 X 10(-11) M for both La3+ and Lu3+. The other site, however, is evidently quite sensitive to the nature of the bound Ln3+ ion and shows a strong preference for La3+ (KD,La = 2.0 X 10(-11) M; KD,Lu = 3.6 X 10(-10) M). We conclude from these observations that reports of nearly indistinguishable CD/EF binding site affinities for parvalbumin complexes of the middle-weight lanthanides (i.e., Eu3+, Gd3+, and Tb3+) are quite reasonable in view of the crossover in relative CD/EF site affinities across the lanthanide series.

Animals↗
PubMed1983

The TOG Club.

The TOG Club (teachers of geriatrics in the London area) was formed in 1972 with the major objective of ensuring that the teaching of geriatric medicine featured in the regulations for the degrees of MB, BS, in the University of London, and by following this up with pressure to have departments of geriatric medicine participate in such teaching. A second objective was to be represented in examinations. Both of these objectives have been attended with a good deal of success, but there are still medical schools in London where teaching on the subject remains rudimentary.

Education, Medical, Undergraduate↗