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Biomedical subjects

T Powell

Publications and source records attributed to T Powell.

At least 127 records · Page 7Linked to original sources
PubMed1982

Femoral venous trauma in a university referral center.

Therapeutic results from extremity vascular injuries have been improved by early definitive care by surgeons trained in peripheral vascular techniques. Serious venous injuries are uncommonly seen other than in large urban referral centers or military installations. Seventeen patients with major femoral venous injuries were evaluated over the past 25 years at the North Carolina Memorial Hospital. The records from these patients were analyzed regarding mechanisms of injury, time delay for definitive care, clinical presentation, significant associated injuries, operative management of the venous injury, early and long-term morbidity, and mortality. Major femoral venous injury was associated with simultaneous arterial injury in 59% of cases. Primary venous repair was performed in seven cases with a satisfactory functional result in all instances. Chronic venous insufficiency developed in five patients (29%), all of whom had arterial injuries and venous ligation. Postoperative complications were commonly related to associated injuries. No patient in this series developed thrombophlebitis or a pulmonary embolus. Isolated femoral vein injuries are usually associated with both early and late favorable results. Femoral vein ligation in the presence of arterial injuries usually leads to serious long-term venous disability. When technically feasible, operative repair of major femoral vein injuries is advocated.

Femoral Vein↗
PubMed1981

Intact individual heart cells isolated from human ventricular tissue.

The intricate architecture of heart muscle, comprising irregularly shaped cells which interdigitate in a complex three-dimensional array, has often compromised clear interpretation of experimental data obtained from the whole organ. One approach to minimise some of the difficulties is to use individual muscle cells in suspension, and data have already been reported using myocytes isolated from mammalian ventricles. It is difficult, however, to extrapolate results obtained from animal tissues to situations of medical relevance in man. Intact isolated muscle cells were obtained from human ventricular tissue by modifications of methods used for isolating smooth muscle, atrial, and ventricular tissue from animals. Electrical studies showed that these myocytes had functional characteristics similar to those observed in the whole heart. Such cells will prove a useful preparation for studies on both the mechanisms underlying myocardial performance in normal and diseased states and the response of heart tissue at the cellular level to conditions found during cardiac surgery.

Action Potentials↗
PubMed1981

Voltage clamp and internal perfusion of single rat heart muscle cells.

1. Single cells from adult rat ventricle were dispersed using an enzymic dissociation technique. Electrical properties were measured with either suction pipettes or conventional glass micropipettes and the results were compared. 2. Suction pipette and micropipette measurements of resting membrane potentials and action potentials were comparable. Values were similar to those reported previously for both dispersed cardiac myocytes and whole tissue preparations from adult rat ventricle. 3. Voltage clamp with a single suction pipette was used in initial experiments, but the results were not sufficiently accurate. Consequently, voltage clamp of single cells was carried out using two suction pipettes (tip diameters 10-15 micrometers), one for passing current and the other for recording membrane potential. Dialysis of cell contents was performed by each suction pipette. A roving micropipette (tip diameter less than 1 micrometer) was used occasionally to measure membrane potential at selected sites. 4. Using the two-suction-pipette method, voltage-clamp steps rose with time constants of less than 10 microsec and the capacitative current transient decayed with a single time constant of less than 100 microsec. These values are more optimal than those observed in other voltage-clamped cardiac muscle preparations. 5. Single cardiac myocytes had membrane input resistances of 44.5 +/- 4.6 M omega, membrane time constants of 16.2 +/- 0.63 msec and membrane capacitances of 399.7 +/- 42.2 pF. (values are means +/- DS, n = 10-). The length constant, lambda, of a single myocte at ists resting potential and perfused with KH2PO4 was about 500 micrometers. For cells perfused with Cs aspartate solution commonly used in voltage-clamp experiments, the input resistance was approximately quadrupled and lambda was 1100 micrometers. The average length of a myocyte partially aspirated by two suction pipettes was 50 micrometers. At maximum -gNa in 50% extracellular Na, lambda was calculated to be about four times the actual cell length between voltage-recording and current-passing pipettes. 6. The half-time for the disappearance or recovery of outward Na currents, following removal or restitution of intracellular Na with two pipettes, was of the order 1 min, indicating that intracellular ionic composition of the cell could be readily controlled and modified.

Action Potentials↗
PubMed1981

Sodium current in single rat heart muscle cells.

1. Rapid inward Na current (INa) was studied in isolated cells from rat ventricular myocardium by a double-suction-pipette voltage clamp technique. All experiments were carried out at 20-22 degrees C. 2. INa elicited by single depolarizing voltage steps from a holding potential, VH, of -80 mV had a threshold between -70 and -60 mV and was maximal at -30 to -20 mV. Peak currents in Krebs-Ringer solution containing 145 mM Na were of the order 0.9-1.8 mA cm-2, assuming an average cell surface area of 8000 square micrometers. 3. The reversal potential for INa was predicted by the Nernst equation for external Na in the range 1.45-145 mM with 16 mM-Na solution perfusing the interior of the cell. 4. Instantaneous I-V plots were linear for potentials of -100 to + 10 mV. Maximum Na conductance (-gNa) was calculated to be 25 mS cm-2 in 145 mM-Na solutions and gNa was constant for potentials positive to -10 mV. 5. INa activated with a time constant of 0.7 msec at -55 mV, decreasing to 100 microsec on depolarizations positive to + 10 mV. 6. Two time constants (tau h1, tau h2) were required to describe INa inactivation during a maintained depolarization, with tau h2 three to four times as long as tau h1. tau h1 was about 2 msec at -50 mV, decreasing to 0.9 msec at -10 mV. 7. The time course for recovery of INa from inactivation also exhibited two time constants (tau r1, tau r2), with the longer tau r2 having a maximum value of the order 100 msec in the potential range -60 to -80 mV. 8. INa in isolated rat cardiac cells has a low sensitivity to tetrodotoxin, requiring a concentration of 30 micrometers for complete blockade.

Animals↗
PubMed1980

Electrical properties of individual cells isolated from adult rat ventricular myocardium.

1. Individual cells were isolated from adult rats ventricular myocardium by a collagenase digestion procedure. 2. Steady membrane potentials recorded with conventional intracellular glass micro-electrodes from cells in a modified Krebs solution containing 3 . 8 mM-KCl and 0 . 5 mM-CaCl2 were less negative than -40 mV in most cells (-25 . 3 +/- 10 . 9 mV, mean +/- S.D., 211 cells). 3. After addition of the potassium selective ionophore valinomycin (60 nM) to the bathing solution all recorded membrane potentials were more negative than -60 mV (-74 . 8 +/- 7 . 0 mV, sixty-three cells). 4. The internal concentration of potassium in the cells was determined as 120 . 8 +/- 1 . 7 mM (+/- S.E., n = 24) by flame emission spectrometry after centrifugation through silicone oil, using tritiated water and D-[1-14C] mannitol to estimate total and extracellular water in the pellet. 5. In the majority of cells in the standard solution the membrane potential recorded within a few msec of penetration was more negative than -70 mV (-78 . 4 +/- 9 . 7 mV, seventy-three cells). In sixty-six cells penetration initiated an action potential which overshot zero by 31 . 3 +/- 7 . 1 mV. This overshoot was abolished by reducing the external sodium to 0 . 1 of the normal value, and reduced or abolished by addition of tetrodotoxin (30 microM). 6. Modifications of the standard bathing solution which increased the number of cells with steady recorded membrane potentials more negative than -60 mV were: isosmotic substitution of sucrose for NaCl; replacement of NaCl and KCl by sodium isethionate and potassium methyl sulphate; addition of 5 or 10 mM-CaCl2; addition of 10 mM-MnCl2. 7. For cells in solution containing 2 . 5 or 5 . 5 mM-CaCl2, input resistances estimated from the amplitude of hyperpolarizations evoked by 200 msec current pulses were approximately 40 M omega at a resting potential close to -80 mV and became much greater as cells were depolarized. Time constants measured at the resting potential were approximately 8 msec. 8. In certain conditions, repeated spontaneous action potentials were recorded from contracting cells, and in quiescent cells evoked action potentials could be initiated by applying brief depolarizing pulses through the micro-electrode. Action potentials were coincident with contractions. 9. It is concluded that the resting potential of these isolated cells is normally more negative than -70 mV, and that the cells retain the ionic mechanisms necessary for the generation of active currents.

Animals↗
PubMed1979

Size measurements on isolated rat heart cells using Coulter analysis and light scatter flow cytometry.

Isolated ventricular muscle cells from the adult rat heart have been examined by both Coulter analysis and light scatter flow cytometry. The dispersed cell preparations contain two main cell types: viable, rod-shaped cells and damaged, round cells. Coulter analytical techniques provided statistical data on cell volume for both cell types. The contribution of each population to the Coulter pulse height distributions were separated by a subtraction method using data obtained from digitonin-treated preparations that contain only round cells. A shape factor for cells aligned with the flow direction was computed from light microscope measurements and the effects of cell orientation within the Coulter aperture were approximately assessed. The estimated volumes for intact myocytes compare favourably with those reported in the literature. No significant size difference was observed between fresh and fixed cells. Narrow angle, forward light scatter measurements were made on individual cells flowing across a focused laser beam. Both scatter pulse height and pulse width (pulse duration) distributions were collected. Values for myocyte length calculated from pulse width information agree well with published data and confirm that the hydrodynamic forces in the flow system produced alignment of the cells with the flow direction. Scatter pulse width distributions reveal two distinct peaks assignable to either rod or round cells. Preliminary electronic gating experiments, using pulse height signals, suggest that signals derived from round cells could be eliminated entirely using a gating regime based on pulse width. This would enable flow cytometric measurements to be made on only the intact myocytes present in heterogeneous preparations.

Animals↗
PubMed1979

The effect of a calcium antagonist (D600) on isoprenaline-induced myocardial necrosis in the rat.

The effect of inhibiting isoprenaline-induced intracellular calcium accumulation on the degree of damage produced in the rat myocardium by this amine has been investigated by simultaneously dosing rats with the calcium antagonistic drug D600. The degree of myocardial necrosis produced in animals given isoprenaline alone and those given D600 was measured by the use of a standard point counting method to show absence of formazan from dead muscle fibres in sections treated to demonstrate succinic dehydrogenase. The use of the calcium antagonistic drug D600 considerably reduced the degree of myocardial damage produced by a standard dose of isoprenaline bitartrate. This was associated with a decrease in the isoprenaline-induced cellular calcium uptake. The results are discussed in relation to the possible protection conferred by lowering of the calcium influx at the cell membrane and the maintenance of the cells' high-energy phosphates at a level which permits "normal" cell function.

Animals↗
PubMed1977

Spontaneous urinary extravasation in non-acute ureteric obstruction: a report of four cases.

Four new cases of spontaneous extravasation of contrast medium during intravenous urography have been described. All were due to non-acute obstruction of the ureter. This is relatively uncommon as most of the cases previously described have been due to passage of a ureteric calculus. Two of the patients improved after relief of the obstruction. In one a nephrectomy was carried out, and one patient died of an unrelated cause before the obstruction could be relieved.

Adult↗