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Biomedical subjects

S S Miller

Publications and source records attributed to S S Miller.

At least 91 records · Page 5Linked to original sources
PubMed1987

Alfalfa Root Nodule Carbon Dioxide Fixation : III. Immunological Studies of Nodule Phosphoenolpyruvate Carboxylase.

Antiserum was prepared in rabbits against purified alfalfa (Medicago sativa L.) nodule phosphoenolpyruvate carboxylase (PEPC). Immunotitration assays revealed that the antiserum recognized the enzyme from alfalfa nodules, uninoculated alfalfa roots, and from soybean nodules. Tandem-crossed immunoelectrophoresis showed that the PEPC protein from alfalfa roots and nodules was immunologically indistinguishable. The 101 kilodalton polypeptide subunit of alfalfa nodule PEPC was identified on Western blots. The PEPC polypeptide was detected in low quantities in young alfalfa roots and nodules but was present at increased levels in mature nodules. Senescent nodules appeared to contain a reduced amount of the PEPC polypeptide. PEPC was also detected by western blot in some plant- and bacterially-conditioned ineffective alfalfa nodules but was not detected in bacteroids isolated from effective nodules. Alfalfa nodule PEPC is constitutively expressed in low levels in roots. In nodules, expression of PEPC polypeptide increases several-fold, resulting in increased PEPC activity. Antiserum prepared against the C(4) PEPC from maize leaves recognized the PEPC enzyme in all legume nodules and roots tested, while the antiserum prepared against alfalfa nodule PEPC also recognized the leaf PEPC of several C(4) plant species. Neither antiserum reacted strongly with any C(3) leaf proteins. The molecular weight of the PEPC polypeptide from C(4) leaves and legume nodules appears to be similar.

Journal Article↗
PubMed1987

Suppressible base substitution mutations induced by angelicin (isopsoralen) in the Escherichia coli lacI gene: implications for the mechanism of SOS mutagenesis.

Angelicin- plus near-UV-induced mutations were umuC dependent in Escherichia coli K-12. Angelicin, a monofunctional psoralen derivative, is believed to damage DNA almost exclusively at pyrimidine bases. To broaden our knowledge about the mutagenic specificity of SOS-dependent mutagens, we determined the mutational specificity of 233 suppressible lacI mutations induced by angelicin. More than 90% of the nonsense mutations arose via transversion substitutions. The three most frequently mutated sites were at A-T base pairs and accounted for more than one-third of all induced nonsense mutations. The two hottest sites were at the only occurrences of the 5'-TATA-3' tetranucleotide in lacI, a sequence expected to be a preferred binding site for a psoralen. Both A-T-to-T-A and A-T-to-C-G transversions were well induced by angelicin treatment, but the frequency of each transversion depended on the particular site. We also detected significant induction of transversion mutations at G-C sites. The induction of transversions by an SOS-dependent mutagen that generates lesions at pyrimidines supports the idea that DNA lesions influence the selection of bases that are incorporated via the process of SOS repair.

Base Sequence↗
PubMed1987

Adenylate cyclase stimulation alters transport in frog retinal pigment epithelium.

The effect of adenylate cyclase inhibitors and activators on enzyme kinetics and cyclic AMP (cAMP) levels was determined in the bullfrog retinal pigment epithelium (RPE). The RPE enzyme has two Km for ATP: 5.2 X 10(-4) and 4.0 X 10(-5) M, with Vmax of 2.5 and 0.25 nmol X mg protein-1 X min-1. Forskolin, the most potent activator, produced a fourfold increase in enzyme activity and, in the presence of isobutylmethylxanthine (IBMX), an inhibitor of phosphodiesterase, caused a 20-fold increase in cAMP levels. Alloxan, a potent inhibitor, blocked the forskolin-induced activation of this enzyme. In the isolated RPE choroid, forskolin (plus IBMX) produced changes in membrane voltage and resistance that were similar in magnitude but slower in time course than those produced by exogenous cAMP. Like exogenous cAMP, forskolin also decreased steady-state fluid and solute transport in isotonic proportions. Therefore, modulation of RPE adenylate cyclase activity plays an important role in the control of RPE transport.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Richter's hernia in the neonate.

Three neonates with small bowel obstruction seen recently at Royal Aberdeen Children's Hospital were found to have a Richter's hernia at laparotomy. In all cases Richter's hernia was at the internal inguinal ring. Two of them had suture of the hernial sac from within the abdomen at the time of laparotomy. These cases have been presented to emphasize the importance of considering Richter's hernia as a possible cause of small bowel obstruction in the neonate and also to indicate that the hernial sacs in such cases could be dealt with by suturing the sac from within the abdomen at the time of laparotomy.

Hernia, Ventral↗
PubMed1986

Congenital mesoblastic nephroma of infancy associated with hypercalcemia.

We report a case of hypercalcemia associated with congenital mesoblastic nephroma. Hypercalcemia was corrected preoperatively and a nephrectomy was performed. Postoperatively, the serum calcium returned to normal. The patient has been followed for more than 18 months, during which time he has remained free of disease with normal serum calcium.

Humans↗
PubMed1985

Enhanced sensitivity of Escherichia coli umuC to photodynamic inactivation by angelicin (isopsoralen).

Escherichia coli umuC cells were inactivated four times more rapidly than umuC+ cells by angelicin (a monofunctional psoralen) plus near-UV irradiation. With other DNA-damaging treatments, either no or much smaller differences in sensitivity were observed. These results show that functions associated with the UmuC+ phenotype contribute to the repair (or tolerance) of some categories of DNA damage more efficiently than others.

Escherichia coli↗
PubMed1984

Effects of cyclic AMP on fluid absorption and ion transport across frog retinal pigment epithelium. Measurements in the open-circuit state.

A modified version of a capacitance probe technique has been used to measure fluid transport across the isolated retinal pigment epithelium (RPE)-choroid of the bullfrog. The accuracy of this measurement is 0.5-1.0 nl/min. Experiments carried out in the absence of external osmotic or hydrostatic gradients show that the RPE-choroid transports fluid from the retinal to the choroid side of the tissue at a rate of approximately 10 nl/min (4-6 microliters/cm2 X h). Net fluid absorption (Jv) was abolished within 10 min by the mitochondrial uncoupler 2,4-dinitrophenol. It was also inhibited (70%) by the removal of bicarbonate from the bulk solutions bathing the tissue. Ouabain caused a slow decrease in Jv (no effect at 10 min, 70% at 3 h), which indicates that RPE fluid transport is not directly coupled to the activity of the Na-K pump located at the apical membrane of this epithelium. In contrast to ouabain, cyclic AMP (cAMP) produced a quick decrease in Jv (84% within 5 min). Radioisotope experiments in the open circuit show that cAMP stimulated secretory fluxes of Na and Cl, which accounted for the observed cAMP-induced decrease in Jv. The direction of net fluid absorption, the magnitudes of the net ionic fluxes in the open circuit, and the dependence of Jv on external bicarbonate concentration strongly suggest that fluid absorption is generated primarily by the active absorption of bicarbonate.

Absorption↗
PubMed1982

Potassium transport across the frog retinal pigment epithelium.

Previous experiments indicate that the apical membrane of the frog retinal pigment epithelium contains electrogenic Na:K pumps. In the present experiments net potassium and rubidium transport across the epithelium was measured as a function of extracellular potassium (rubidium) concentration, [K]0 ( [Rb]0). The net rate of retina-to-choroid 42K(86Rb) transport increased monotonically as [K]0 ( [Rb]0) increased from approximately 0.2 to 5 mM on both sides of the tissue or on the apical (neural retinal) side of the tissue. No further increase was observed when [K]0 ( [Rb]0) was elevated to 10 mM. Net sodium transport was also stimulated by elevating [K]0. The net K transport was completely inhibited by 10-4 M ouabain in the solution bathing the apical membrane. Ouabain inhibited the unidirectional K flux in the direction of net flux but had no effect on the back-flux in the choroid-to-retina direction. The magnitude of the ouabain-inhibitable 42K(86Rb) flux increased with [K]0 ( [Rb]0). These results show that the apical membrane Na:K pumps play an important role in the net active transport of potassium (rubidium) across the epithelium. The [K]0 changes that modulate potassium transport coincide with the light-induced [K]0 changes that occur in the extracellular space separating the photoreceptors and the apical membrane of the pigment epithelium.

Animals↗
PubMed1982

Fluid transport across retinal pigment epithelium is inhibited by cyclic AMP.

Fluid transport across the retinal pigment epithelium (bullfrog) has been measured. These experiments were carried out by using a capacitance probe technique and a water-impermeable chamber that allowed the measurements to be made with an accuracy of 0.5-1.0 nl/min. With identical Ringer's solution on both sides of the epithelium, and in the absence of a hydrostatic driving force, the direction of net fluid movement is from the retina to the choroid (absorption). The net transport rate, approximately 10 nl/min (4.8 microliters/cm2 . hr), is comparable to that observed in other amphibian epithelia. It is reduced to zero by the mitochondrial uncoupler 2,4-dinitrophenol but is relatively unaffected by ouabain, which inhibits the Na+/K+-pump located on the apical membrane of this epithelium. A significant decrease in net fluid absorption was produced by dibutyryl cAMP and 3-isobutyl-1-methylxanthine (a potent phosphodiesterase inhibitor). This cAMP-dependent fluid transport may be an important mechanism for controlling the fluid volume in the subretinal space.

1-Methyl-3-isobutylxanthine↗
PubMed1981

Intravenous radionuclide cystography for the detection of vesicorenal reflux.

Intravenous radionuclide cystography using a single intravenous injection of 99mtechnetium diethylenetriaminepentaacetic acid, provides information on individual kidney function, coarse anatomy and vesicorenal reflux. This study investigates the effectiveness of intravenous radionuclide cystography in detecting reflux. In 58 children intravenous radionuclide cystography detected 53 ureters with reflux compared to 32 detected by voiding cystography. This difference was investigated further with patients in whom other test suggested reflux. While there was no statistically significant difference for patients having pyelonephritis or hydronephrosis, intravenous radionuclide cystography detected significantly more ureters with reflux in patients with abnormal ureteral orifices or infected urine and, therefore, predisposed to reflux. Intravenous radionuclide cystography is a more comprehensive and sensitive test for vesicorenal reflux than voiding cystography.

Adolescent↗