Biomedical subjects

P Taber

Publications and source records attributed to P Taber.

At least 19 recordsLinked to original sources

PubMed1991

Response of chloride efflux from skeletal muscle of Rana pipiens to changes of temperature and membrane potential and diethylpyrocarbonate treatment.

Efflux of 36Cl- from frog sartorius muscles equilibrated in two depolarizing solutions was measured. Cl- efflux consists of a component present at low pH and a pH-dependent component which increases as external pH increases. For temperatures between 0 and 20 degrees C, the measured activation energy is 7.5 kcal/mol for Cl- efflux at pH 5 and 12.6 kcal/mol for the pH-dependent Cl- efflux. The pH-dependent Cl-efflux can be described by the relation mu = 1/(1 + 10n(pK alpha-pH], where mu is the Cl- efflux increment obtained on stepping from pH 5 to the test pH, normalized with respect to the increment obtained on stepping from pH 5 to 8.5 or 9.0. For muscles equilibrated in solutions containing 150 mM KCl plus 120 mM NaCl (internal potential about -15 mV), the apparent pK alpha is 6.5 at both 0 and 20 degrees C, and n = 2.5 for 0 degrees C and 1.5 for 20 degrees C. For muscles equilibrated in solutions containing 7.5 mM KCl plus 120 mM NaCl (internal potential about -65 mV), the apparent pK alpha at 0 degrees C is 6.9 and n is 1.5. The voltage dependence of the apparent pK alpha suggests that the critical pH-sensitive moiety producing the pH-dependent Cl- efflux is sensitive to the membrane electric field, while the insensitivity to temperature suggests that the apparent heat of ionization of this moiety is zero. The fact that n is greater than 1 suggests that cooperativity between pH-sensitive moieties is involved in determining the Cl- efflux increment on raising external pH. The histidine-modifying reagent diethylpyrocarbonate (DEPC) applied at pH 6 reduces the pH-dependent Cl- efflux according to the relation, efflux = exp(-k.[DEPC].t), where t is the exposure time (min) to DEPC at a prepared initial concentration of [DEPC] (mM). At 17 degrees C, k-1 = 188 mM . min. For temperatures between 10 and 23 degrees C, k has an apparent Q10 of 2.5. The Cl- efflux inhibitor SCN- at a concentration of 20 mM substantially retards the reduction of the pH-dependent Cl- efflux by DEPC. The findings that the apparent pK alpha is 6.5 in depolarized muscles, that DEPC eliminates the pH-dependent Cl- efflux, and that this action is retarded by SCN- supports the notion that protonation of histidine groups associated with Cl- channels is the controlling reaction for the pH-dependent Cl- efflux.

Animals↗

PubMed1991

Mapping intravascular extension of Wilms' tumor with magnetic resonance imaging.

Accurate preoperative diagnosis of renal vein, vena caval, or intracardiac extension of Wilms' tumor allows the surgeon to better plan operative vascular control and assess the potential benefits of preoperative chemotherapy. Magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound were used to study four consecutive patients presenting with Wilms' tumor. Three had vena caval involvement, with one of these having a massive right atrial tumor thrombus. A fourth patient had renal vein involvement only. We found MRI to be superior to both CT and ultrasound for mapping intravascular extension of Wilms' tumor and for delineating nonvascular disease. Because of its noninvasiveness, multiplane imaging capabilities, and image contrast and resolution, MRI is a valuable complimentary imaging modality for the diagnosis and follow-up of patients with Wilms' tumor.

Child, Preschool↗

PubMed1990

Zinc inhibition of chloride efflux from skeletal muscle of Rana pipiens and its modification by external pH and chloride activity.

Efflux of 36Cl- from frog sartorius muscles equilibrated in depolarizing solutions was measured. Cl- efflux consists of a component present at low pH and a pH-dependent component which increases as external pH increases. In depolarized muscles from Rana pipiens, the pH-dependent Cl- efflux has an apparent pKa near 6.4. The reduction of Cl- efflux by external Zn2+ was determined at different external pHs and chloride activities. The effect of external chloride activity on the pH-dependent Cl- efflux was also examined. At pH 6.5 and a membrane potential of -22 mV, increasing external Cl- activity from 0.108 to 0.28 M decreased inhibition of the pH-dependent Cl- efflux at all activities of Zn2+. The Zn2+ activity needed to reduce Cl- efflux by half increased from 0.39 x 10(-3) to 2.09 x 10(-3) M. By contrast, external Cl- activity had no measurable effect on the apparent pKa of the pH-dependent efflux. At constant Cl- activity less than 0.21 M, increasing external pH from 6.5 to 7.5 decreased inhibition by low Zn2+ activities with either a slight increase or no change in the Zn2+ activity producing half-inhibition. In other words, for relatively low Cl- activities, protection against inhibition of Cl- efflux by low Zn2+ activities was obtained by raising, not lowering, external pH; this is not what is expected if H+ and Zn2+ ions compete at the same site to produce inhibition of Cl- efflux. We conclude that Zn2+ and low pH inhibit Cl- efflux by separate and distinct mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Use of MRI in evaluation of anorectal anomalies.

Congenital anorectal anomalies present with a wide spectrum of anatomical deformity. The level of atresia, the extent of the development of the pelvic musculature, and the presence of associated anomalies all greatly influence treatment options. Further complexity may be introduced by previous attempts at correction. Magnetic resonance imaging (MRI) recently has been suggested as an effective tool in evaluation of such patients for surgical repair. Thirteen patients undergoing evaluation for either primary or secondary operations for imperforate anus were studied with MRI. Age range was newborn to 26 years. These patients had anorectal deformities in various stages of treatment--from newly diagnosed imperforate anus in the newborn to patients who had undergone previous surgical repair of their deformity with poor results. In newborns, MRI was very useful in assessing the level of atresia and determining whether perineal repair was advisable. In older patients with high atresias, MRI was useful in planning operative strategy and predicting the outcome by providing information about the pelvic musculature. This information was directly related to the size of the patient, ie, the larger, and therefore the older the patient, the more detail MRI provided about the pelvic musculature. Especially in secondary cases, this information proved to be helpful in determining the cause of the initial failure, ie, lack of adequate pelvic musculature or poor placement of the distal colon in relation to the striated muscle complex at the initial operation. MRI demonstrated previous unsuspected lesions such as tethered cord, sacral deformity or urinary tract abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1989

Congenital metastatic cervical teratoma: diagnostic and management considerations.

Cervical teratomas in the newborn are uncommon and difficult management problems, as their natural history and prognosis are not well defined. Existing or potential airway obstruction is usually the main concern in acute management of these patients. Total excision is essential to avoid local recurrence in benign lesions, and a small but present risk of malignancy can result in death from metastatic lesions which appear later. A unique case of neonatal malignant cervical teratoma with large congenital metastatic lesions present in liver, lung, and buttocks was successfully managed. Magnetic resonance imaging (MRI) was invaluable, both in delineating these lesions and in planning a four-stage curative resection of all macroscopic disease. Such a case has not been reported previously.

Female↗

PubMed1989

Use of magnetic resonance imaging in planning the separation of omphalopagus conjoined twins.

Magnetic resonance imaging (MRI) was used for the first time in the preoperative planning for separation of conjoined twins. In these omphalopagus infants, MRI showed normal biliary and cardiovascular structures and demonstrated, in detail, a relatively avascular plane through the liver bridge, which enabled safe separation with minimal blood loss at 3 1/2 months of age. A single MRI study supplied information superior to that obtained with multiple previously available imaging studies. MRI should be an essential part of the preoperative workup of all types of conjoined twins.

Abdomen↗

PubMed1988

Effective thrombolytic therapy of aortic thrombosis in the small premature infant.

Aortic thrombosis in the very-low-birthweight premature infant has remained both a diagnostic and a therapeutic dilemma. Nine small infants were evaluated for symptoms of extremity and/or visceral ischemia. All were found to have aortoiliac thrombosis most likely related to indwelling umbilical artery catheters. Diagnostic and therapeutic options were evaluated. An angiogram obtained through the catheter was found to be the most effective diagnostic technique. Local infusion of intra-arterial streptokinase (50 U/kg/h) directly into the clot for 36 hours resulted in resolution of ischemic symptoms. No complications were encountered with the use of this protocol.

Aorta, Abdominal↗

PubMed1979