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D S Williams

Publications and source records attributed to D S Williams.

At least 19 recordsLinked to original sources
PubMed2000

Changes in cerebral blood flow and distribution associated with acute increases in plasma sodium and osmolality of chronic hyponatremic rats.

The cause of the osmotic demyelination syndrome that follows too rapid correction of chronic hyponatremia (CHN) is unknown. Recently, we reported in CHN rats an association between blood-brain barrier (BBB) disruption occurring as early as 3 h into correction and subsequent demyelination. Given the changes in brain water and blood volume which occur during correction of CHN, we hypothesized that the same correction protocol that causes demyelination might alter cerebral blood flow (CBF) during correction, thereby possibly contributing to BBB disruption and demyelination. Ten CHN rats were given hypertonic sodium intraperitoneally and its effect on CBF was continuously monitored for 3 h by magnetic resonance flow imaging. Over the subsequent 3 h, plasma sodium rose from 110.8 to 127.6 mEq/liter (P < 0.001) but neither mean arterial blood pressure nor arterial CO(2) tension changed significantly. By 30 min, CBF increased by 50% in cortical and subcortical areas (P < 0.001) and remained elevated for the next 60 min. After 2 h, cortical flow was no longer elevated significantly and by 3 h it had returned to control values. Subcortical flow, however, significantly exceeded control values throughout the 3 h so that after 2 h the ratio of cortical to subcortical blood flow had fallen from 1.17 to 0.91 (P < 0.05). Although the mechanism by which increased plasma sodium and osmolality alters CBF is uncertain, the results suggest that changes in CBF may be part of a cascade of cerebrovascular disturbances including endothelial or parenchymal damage, mechanical events, metabolic disturbances, or cytokine release which eventually lead to BBB disruption and subsequent demyelination.

Animals↗
PubMed2000

Positive association between blood brain barrier disruption and osmotically-induced demyelination.

Rapid correction of chronic hyponatremia can cause osmotic brain demyelination in animals and humans. Why demyelination develops is unknown, but blood brain-barrier disruption might expose oligodendrocytes to substances normally excluded from the brain. To test this hypothesis, chronic hyponatremia was induced and corrected using a new, reproducible rat model for producing osmotic brain demyelination. Blood brain barrier integrity was assessed by NMR imaging at either 3, 16 or 24 h during the first day of correction. Demyelination was determined histopathologically 5 - 6 days later. Of 96 rats studied, demyelination developed 5 - 6 days later in 37 rats, 89% of whom showed barrier disruption. In the 59 rats who did not develop demyelination, 45 (76%) had no barrier disruption. Thus, blood-brain barrier disruption during the first 24 h of correction was associated with a 70% risk of developing demyelination. By contrast, the risk of developing subsequent demyelination was only 8% when the barrier was intact. This strong association between barrier disruption and subsequent demyelination provides new insights into the role of blood brain barrier function in demyelinative disorders such as the osmotic demyelination syndrome and by extension to other demyelinative disorders such as multiple sclerosis.

Animals↗
PubMed1999

Myosin VIIa participates in opsin transport through the photoreceptor cilium.

Two types of Usher syndrome, a blindness-deafness disorder, result from mutations in the myosin VIIa gene. As for most other unconventional myosins, little is known about the function or functions of myosin VIIa. Here, we studied the photoreceptor cells of mice with mutant myosin VIIa by electron immunomicroscopy and microscopic autoradiography. We found evidence that myosin VIIa functions in the connecting cilium of each photoreceptor cell and participates in the transport of opsin through this structure. These findings provide the first direct evidence that opsin travels along the connecting cilium en route to the outer segment. They demonstrate that a myosin may function in a cilium and suggest that abnormal opsin transport might contribute to blindness in Usher syndrome.

Animals↗
PubMed1999

Perfusion analysis using dynamic arterial spin labeling (DASL).

A variety of magnetic resonance (MR) techniques have proved useful to quantify perfusion using endogenous water as a blood flow tracer. Assuming that water is a freely diffusable tracer, the model used for these techniques predicts that the quantitation of perfusion is based on three parameters, all of which can depend on blood flow. These are the longitudinal tissue relaxation time, the transit time from point of labeling to tissue, and the difference in tissue MR signal between an appropriate control and the labeled state. To measure these three parameters in parallel, a dynamic arterial spin labeling (DASL) technique is introduced based on the analysis of the tissue response to a periodic time varying degree of arterial spin labeling, called here the labeling function (LF). The LF frequency can be modulated to overdetermine parameters necessary to define the system. MR schemes are proposed to measure the tissue response to different LF frequencies efficiently. Sprague-Dawley rats were studied by DASL, using various frequencies for the LF and various arterial pCO2 levels. During data processing, the periodic behavior of the tissue response to the LF allowed for frequency filtering of periodic changes in signal intensity unrelated to perfusion and arterial spin labeling. Measures of transit time, tissue longitudinal relaxation time, and perfusion agreed well over a range of LF frequencies and with previous results. DASL shows potential for more accurately quantifying perfusion as well as measuring transit times associated with arterial spin labeling techniques.

Animals↗
PubMed1999

Early perfusion after controlled cortical impact in rats: quantification by arterial spin-labeled MRI and the influence of spin-lattice relaxation time heterogeneity.

Early posttraumatic cerebral hypoperfusion is implicated in the evolution of secondary damage after experimental and clinical traumatic brain injury (TBI). This is the first report of cerebral blood flow (CBF) measurement by continuous arterial spin-labeled magnetic resonance imaging (MRI) early after TBI in rats using the controlled cortical impact (CCI) model. CCI reduced CBF globally at approximately 3 hr (versus normal), with 85% and 49% reductions in a contused cortical region and contralateral cortex, respectively. In contrast, a prior MRI study from this laboratory showed at 24 hr post trauma a focal CBF reduction restricted to the injury site. In vivo spin-lattice relaxation time (T(1obs)), which is used in CBF quantification, was spatially heterogeneous early after CCI, a time when edema is developing in injured brain tissue. At 4.7 T, T(1obs) values are increased 29% in the contusion (versus normal), consequently reducing CBF quantification to a similar degree. MRI should facilitate coupling posttraumatic CBF with long-term functional outcome. Magn Reson Med 42:673-681, 1999.

Animals↗
PubMed1999

Detection of single mammalian cells by high-resolution magnetic resonance imaging.

This study reports the detection of single mammalian cells, specifically T cells (T lymphocytes) labeled with dextran-coated superparamagnetic iron oxide particles, using magnetic resonance microscopy. Size amplification due to sequestration of the superparamagnetic particles in vacuoles enhances contrast in localized areas in high-resolution magnetic resonance imaging. Magnetic resonance images of samples containing differing concentrations of T cells embedded in 3% gelatin show a number of dark regions due to the superparamagnetic iron oxide particles, consistent with the number predicted by transmission electron microscopy. Colabeling of T cell samples with a fluorescent dye leads to strong correlations between magnetic resonance and fluorescence microscopic images, showing the presence of the superparamagnetic iron oxide particles at the cell site. This result lays the foundation for our approach to tracking the movement of a specific cell type in live animals and humans.

Animals↗
PubMed1999

Cardiac function of transplanted rat hearts using a working heart model assessed by magnetic resonance imaging.

BACKGROUND: A direct correlation between graft rejection and cardiac contractile function in small-animal models has been difficult to establish because (i) the conventional non-working heart model is greatly different from the orthotopic heart in terms of left ventricular work and (ii) it is difficult to obtain hemodynamic data in situ. We have used magnetic resonance imaging (MRI) techniques to obtain noninvasive, in-situ quantitation of ventricular volume after heterotopic cardiac transplantation. METHODS: Infra-renal heterotopic cardiac transplantation was performed on rats using syngeneic and allogeneic untreated donors in both working and non-working left heart models. An occluding balloon catheter in the inferior vena cava was used to vary the pre-load to the graft. An arteriovenous fistula was created to raise inferior caval oxygen saturation. Magnetic resonance imaging measurements were carried out at day 3, 4, and 5 post-transplantation. Left ventricle end-diastolic and end-systolic volumes were calculated using a biplanar ellipsoid model. RESULTS: Stroke volume was significantly increased in the working heart model as compared to the non-working model. At day 4 post-transplant, the diastolic pressure-volume relationship in the allograft group was significantly shifted, indicative of decreased myocardial distensibility, whereas the indices of systolic function were preserved. CONCLUSIONS: We have developed a heterotopic transplant working rat heart model and have used it to assess in-situ cardiac function by MRI. Sensitive indices of diastolic contractile function can be obtained in this rodent transplant model that correlate well with histologic evidence of early rejection.

Animals↗
PubMed1999

The propanediol utilization (pdu) operon of Salmonella enterica serovar Typhimurium LT2 includes genes necessary for formation of polyhedral organelles involved in coenzyme B(12)-dependent 1, 2-propanediol degradation.

The propanediol utilization (pdu) operon of Salmonella enterica serovar Typhimurium LT2 contains genes needed for the coenzyme B(12)-dependent catabolism of 1,2-propanediol. Here the completed DNA sequence of the pdu operon is presented. Analyses of previously unpublished pdu DNA sequence substantiated previous studies indicating that the pdu operon was acquired by horizontal gene transfer and allowed the identification of 16 hypothetical genes. This brings the total number of genes in the pdu operon to 21 and the total number of genes at the pdu locus to 23. Of these, six encode proteins of unknown function and are not closely related to sequences of known function found in GenBank. Two encode proteins involved in transport and regulation. Six probably encode enzymes needed for the pathway of 1,2-propanediol degradation. Two encode proteins related to those used for the reactivation of adenosylcobalamin (AdoCbl)-dependent diol dehydratase. Five encode proteins related to those involved in the formation of polyhedral organelles known as carboxysomes, and two encode proteins that appear distantly related to those involved in carboxysome formation. In addition, it is shown that S. enterica forms polyhedral bodies that are involved in the degradation of 1,2-propanediol. Polyhedra are formed during either aerobic or anaerobic growth on propanediol, but not during growth on other carbon sources. Genetic tests demonstrate that genes of the pdu operon are required for polyhedral body formation, and immunoelectron microscopy shows that AdoCbl-dependent diol dehydratase is associated with these polyhedra. This is the first evidence for a B(12)-dependent enzyme associated with a polyhedral body. It is proposed that the polyhedra consist of AdoCbl-dependent diol dehydratase (and perhaps other proteins) encased within a protein shell that is related to the shell of carboxysomes. The specific function of these unusual polyhedral bodies was not determined, but some possibilities are discussed.

Cloning, Molecular↗
PubMed1998

Regulation of the phosphorylation state of rhodopsin by dopamine.

G protein-coupled receptors (GPCRs) are regulated by kinases and phosphatases that control their phosphorylation state. Here, the possibility that the state of GPCR phosphorylation could be affected by paracrine input was explored. We show that dopamine increased the rate of dephosphorylation of rhodopsin, the light receptor, in intact frog retinas. Further, we found that rod outer segments from dopamine-treated retinas contained increased rhodopsin phosphatase activity, indicating that this effect of dopamine on rhodopsin was mediated by stimulation of rhodopsin phosphatase. Dopamine is a ubiquitous neuromodulator and, in the retina, is released from the inner cell layers. Thus, our results identify a pathway for feedback regulation of rhodopsin from the inner retina and illustrate the involvement of dopamine in paracrine regulation of the sensitivity of a GPCR.

Animals↗
PubMed1998

Myosin VIIa as a common component of cilia and microvilli.

The distribution of myosin VIIa, which is defective or absent in Usher syndrome 1B, was studied in a variety of tissues by immunomicroscopy. The primary aim was to determine whether this putative actin-based mechanoenzyme is a common component of cilia. Previously, it has been proposed that defective ciliary function might be the basis of some forms of Usher syndrome. Myosin VIIa was detected in cilia from cochlear hair cells, olfactory neurons, kidney distal tubules, and lung bronchi. It was also found to cofractionate with the axonemal fraction of retinal photoreceptor cells. Immunolabeling appeared most concentrated in the periphery of the transition zone of the cilia. This general presence of a myosin in cilia is surprising, given that cilia are dominated by microtubules, and not actin filaments. In addition to cilia, myosin VIIa was also found in actin-rich microvilli of different types of cell. We conclude that myosin VIIa is a common component of cilia and microvilli.

Animals↗
PubMed1998

Cardiac MRI of the normal and hypertrophied mouse heart.

With the development of recent transgenic techniques, studies involving mice offer opportunities to increase understanding of cardiac disease. This provides motivation for the current study to perform noninvasive evaluation of the normal and hypertrophied mouse heart with MRI. By acquiring ECG and respiratory signals, the MR image acquisition was gated to both the cardiac and respiratory cycles. Combining a spin-warp imaging sequence with an RF surface coil resulted in short-axis images that allowed quantification of in vivo cardiac mass. Excellent agreement between MRI-determined (y) and postmortem heart weight (x) was obtained: y = 0.991x + 1.43 (r = 0.996). Isoproterenol, at 282 micromol/kg body weight (BW) and 573 micromol/kg BW, induced a dose-dependent increase in the ratio of heart weight to BW of 16.8 +/- 1.09% and 24.1 +/- 1.71%, respectively, which was accurately measured by MRI. These results demonstrate the ability of MRI to noninvasively monitor cardiac anatomy in the mouse.

Animals↗
PubMed1998

Perfusion quantitation in transplanted rat kidney by MRI with arterial spin labeling.

The purpose of this study was to determine the feasibility of using quantitative magnetic resonance imaging (MRI) with non-invasive arterial spin labeling to assess perfusion of transplanted kidneys in rats. MRI studies were performed on five groups of rats: normal Fisher 344 rats, Fisher 344 rats that had received a syngeneic kidney transplant either 3 or seven days prior to study, and Fisher 344 rats that had received an allogeneic kidney (ACI rat as the donor) either three or seven days prior to study. The contralateral native kidney remained in place for comparison. Cortical perfusion was quantitated from a slice through the center of each kidney in anesthetized rats at 4.7 Tesla with a fast gradient-echo MRI sequence following the arterial spin labeling. The spin-lattice relaxation time was measured within the cortex, and the cross sectional area of the kidney was also determined within the same MRI plane. Immediately after the perfusion imaging measurement, transplanted kidneys were removed and scored for rejection using the Banff histological criteria. Renal cortical perfusion in normal kidneys was 7.5 +/- 0.8 ml/g/min (N = 12 rats, 24 kidneys). At the third day post-transplantation, that is, before marked acute rejection, the renal cortical perfusion rate was similar in both syngeneic and allogeneic kidneys [3.3 +/- 1.7 (N = 6) and 3.0 +/- 2.4 ml/g/min (N = 6), respectively]. In contrast, at the seventh day post-transplantation, that is, during severe rejection, the renal cortical perfusion rate in allogeneic kidneys was very low (undetectable) compared to the value in syngeneic kidneys [that is, < or = 0.3 (N = 6) versus 5.2 +/- 2.0 ml/g/min (N = 6), respectively]. Moreover, the renal cortical perfusion rate determined by MRI was significantly (P < 0.05, r = -0.82) correlated with histological rejection. We conclude that the quantitative measurement of renal cortical perfusion by MRI with arterial spin-labeling could provide a non-invasive diagnostic method for monitoring the status of renal transplants without requiring the administration of a contrast agent.

Acute Disease↗
PubMed1998

Renal vascular responses to angiotensin II in conscious spontaneously hypertensive and normotensive rats.

It has been postulated that exaggerated renal sensitivity to angiotensin II may be involved in the development and maintenance of hypertension in the spontaneously hypertensive rat (SHR). The purpose of this study was to compare the renal vascular responses to short-term angiotensin II infusions (50 ng/kg/min, i.v.) in conscious SHRs and Wistar-Kyoto (WKY) rats. Renal cortical blood flow was measured in conscious rats by using quantitative renal perfusion imaging by magnetic resonance, and blood pressure was measured by an indwelling carotid catheter attached to a digital blood pressure analyzer. Renal vascular responses to angiotensin II were similar in control SHRs and WKY rats. Pretreatment with captopril to block endogenous production of angiotensin II significantly augmented the renal vascular response to exogenous angiotensin II in the SHRs but not in the WKY rats. The renal vascular responses to angiotensin II were significantly greater in captopril-pretreated SHRs than in WKY rats (cortical blood flow decreased by 1.66 +/- 0.13 ml/min/g cortex in WKY rats compared with 2.15 +/- 0.14 ml/min/g cortex in SHR; cortical vascular resistance increased by 10.5 +/- 1.4 mm Hg/ml/min/g cortex in WKY rats compared with 15.6 +/- 1.7 mm Hg/ml/min/g cortex in SHRs). Responses to angiotensin II were completely blocked in both strains by pretreatment with the angiotensin II AT1-receptor antagonist losartan. Results from this study in conscious rats confirm previous findings in anesthetized rats that (a) the short-term pressor and renal vascular responses to angiotensin II are mediated by the AT1 receptor in both SHRs and WKY rats, and (b) the renal vascular responses to angiotensin II are enhanced in SHRs compared with WKY rats when endogenous production of angiotensin II is inhibited by captopril pretreatment.

Angiotensin II↗
PubMed1998

Extraskeletal chondroma of the foot.

Extraskeletal chondroma is a rare, benign cartilaginous tumor seen most frequently in the soft tissues of the hands and feet. The authors present a case of extraskeletal chondroma in a 52-year-old male patient who had a small mass on the left foot involving the flexor surface of the second toe. Radiographs showed the presence of a soft-tissue mass with scattered calcified foci. Surgical excision revealed a benign, lobulated cartilaginous tumor with prominent areas of calcification. Histologically; the lesion consisted of cartilage cells with centralized zones of cellular pleomorphism and giant-cell proliferation at the tumor margin consistent with extraskeletal chondroma.

Chondroma↗
PubMed1997

Purification and light-dependent phosphorylation of a candidate fusion protein, the photoreceptor cell peripherin/rds.

The proteins peripherin/rds and rom-1 form a protein complex in the rims of photoreceptor outer segment disk membranes. Peripherin/rds plays an essential role in the morphogenesis and maintenance of disk membrane structure, with peripherin/rds gene mutations resulting in photoreceptor cell degeneration. We report two different chromatographic procedures for the purification of native peripherin/rds from bovine photoreceptor cell outer segments and show that the protein is a phosphoprotein that promotes membrane fusion in vitro. During one procedure, peripherin/rds was copurified in association with rom-1 by hyroxylapatite and Mono Q FPLC. During the other, it was purified free from rom-1 by concanavalin-A affinity chromatography and chromatofocusing. Analysis of homogeneous peripherin/rds from the second procedure showed that exposure of photoreceptor outer segments to light resulted in the incorporation of nearly 2 mol of phosphate per mole of peripherin/rds and a concomitant shift in the isoelectric point of the protein. In addition, we found that recombination of purified peripherin/rds into lipid vesicles increased membrane fusion, with more rapid fusion detected with phosphorylated peripherin/rds. In conclusion, studies with purified peripherin/rds reveal that the protein undergoes light-dependent phosphorylation and that it may function in membrane fusion.

Amino Acid Sequence↗
PubMed1997

Identification of protein kinase C phosphorylation sites on bovine rhodopsin.

The protein kinase C phosphorylation sites on bovine rhodopsin were identified using proteolytic, phosphoamino acid, mass spectrometric, and peptide sequencing analyses. Tryptic removal of the 9 carboxyl-terminal residues of rhodopsin revealed that a major fraction of the phosphates incorporated by protein kinase C are in a region containing Ser334, Thr335, and Thr336. Phosphoamino acid analysis of the tryptic product established that Ser334 accounts for approximately 65% of the phosphorylation in this region. Analysis of the endoproteinase Asp-N-generated carboxyl terminus of rhodopsin by mass spectrometry and peptide sequencing revealed that Ser338 is also a primary phosphorylation site, with minor phosphorylation of Ser343. Quantitation of high pressure liquid chromatography-separated phosphopeptides, taken together with phosphoamino acid analysis of the tryptic product, revealed that Ser334 and Ser338 were phosphorylated equally and each accounted for approximately 35% of the total phosphorylation; Thr335/336 accounted for just under 20% of the phosphorylation, and Ser343 accounted for 10%. Thus, the primary protein kinase C sites are Ser334 and Ser338, with minor phosphorylation of Thr335/336 and Ser343. Ser334 and Ser338 have recently been identified as the primary sites of phosphorylation of rhodopsin in vivo (Ohguro, H., Van Hooser, J. P., Milam, A. H., and Palczewski, K. (1995) J. Biol. Chem. 270, 14259-14262). Of these sites, only Ser338 is a significant substrate for rhodopsin kinase in vitro. Identification of Ser334 as a primary protein kinase C target in vitro is consistent with protein kinase C modulating the phosphorylation of this site in vivo.

Amino Acid Sequence↗
PubMed1997

Contribution of protein kinase C to the phosphorylation of rhodopsin in intact retinas.

Similar to other G protein-coupled receptors, the visual receptor, rhodopsin, is phosphorylated by both a substrate-regulated kinase, rhodopsin kinase, and a second messenger-regulated kinase, protein kinase C. In the present study, the extent of involvement of protein kinase C in the light-dependent phosphorylation of rhodopsin in intact retinas was assessed using a specific activator (phorbol ester) and specific inhibitor (calphostin C) of protein kinase C. Kinetic analysis of rhodopsin phosphorylation following different illumination conditions revealed that hyperactivation of protein kinase C with phorbol ester resulted in a relative increase in rhodopsin phosphorylation that peaked 10-15 min after the onset of illumination. Following this period, the rate of rhodopsin dephosphorylation was increased in the phorbol ester-treated retinas, so that by about 30 min the amount of phosphorylation was similar to that in control retinas. Treatment of retinas with calphostin C, a potent regulatory domain-directed inhibitor of protein kinase C, resulted in an approximately 50% reduction in the light-dependent phosphorylation of rhodopsin. This inhibitor had no effect on the activity of rhodopsin kinase in vitro. Last, we show that frog rhodopsin is phosphorylated in vitro by protein kinase C from frog rod outer segments, indicating that this kinase could directly modulate rhodopsin in vivo. In conclusion, the present results reveal that the kinetics of rhodopsin phosphorylation/dephosphorylation differ markedly, depending on whether protein kinase C or rhodopsin kinase activity dominates, and that, under the conditions studied, protein kinase C contributes to approximately half of the phosphorylation of rhodopsin in intact frog retinas.

Animals↗