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Biomedical subjects

J G Blackburn

Publications and source records attributed to J G Blackburn.

At least 19 recordsLinked to original sources
PubMed1989

Cadmium nephrotoxicity in human proximal tubule cell cultures.

Human proximal tubule kidney cells grown in a serum-free tissue culture medium were exposed to concentrations of CdCl2 in a range of 0.5 to 10 micrograms/ml. Cells were observed from 1 to 20 d upon initiation of cadmium in the culture fluid. Both confluent and subconfluent populations of cells were treated and evaluated for cytotoxicity. Both populations exhibited a concentration-dependent toxicity to ionic cadmium. For cells treated with 2.0 to 10 micrograms/ml Cd, the decreases in cell numbers were largely irreversible. However, cells treated with Cd in a range of 0.5 to 1.0 micrograms/ml exhibited a partial recovery of cell number and control morphology. In this range, recovery was more efficient in the subconfluent cultures. Fine structural alterations in Cd-treated tubule cells included condensation of nuclear chromatin, loss of microvilli structure, disorganization of lateral membrane interdigitation, as well as decreased uptake of aminoglycoside antibiotics as evidenced by decreased numbers of myeloid bodies in these cells. The results of this study imply that use of a human proximal tubule culture system has potential in discerning structural and functional effects of cadmium as well as other nephrotoxic metals and compounds on the human kidney.

Cadmium↗
PubMed1989

An electrophysiological freeze fracture assessment of cadmium nephrotoxicity in vitro.

Human proximal tubule cell cultures exposed to doses of cadmium chloride (CdCl2) between 0.05 microgram/ml and 0.5 microgram/ml exhibited alterations in cell membrane structure and transport function. At these Cd concentrations, cell numbers were not significantly altered from control values in either nonreplicating confluent, or actively replicating subconfluent cultures. Transmission electron microscopy revealed few alterations in cultures treated with 0.05 microgram/ml Cd. Tight junctions were intact; organelles and myeloid body formation appeared normal. Freeze fracture analysis confirmed the integrity of the tight junctions as well as increased numbers of vesicles or pits along the lateral cell membrane, indicating increased endocytotic activity. Cells exposed to 0.1 microgram/ml Cd were characterized by decreased numbers of microvilli and inhibited myeloid body formation. Cd doses of 0.5 micrograms/ml elicited nuclear chromatin condensation, fragmented sealing strands in 5 to 10% of the tight junction profiles, sparse microvilli, and inhibited myeloid body formation. Electrophysiologic assessments of transport function by Ussing chamber analysis revealed decreases in transepithelial potentials for all three concentrations, with significant differences at Cd concentrations of 0.5 to 0.1 micrograms/ml. Cells treated with 0.5 micrograms/ml Cd also exhibited slight decreases in electrical resistance, consistent with the minimal fragmentation of sealing strands observed in freeze fracture replicas. Resistance in cultures treated with 0.1 or 0.05 micrograms/ml Cd remained within control values and indicated that drops in potential difference and short circuit current in these cells reflected true alterations in ion transport.

Biological Transport↗
PubMed1989

Elevated glucose alters paracellular transport of cultured human proximal tubule cells.

Cultures of human proximal tubule cells were exposed to elevated concentrations of glucose and dome formation was assessed over a 22 day period of growth. Cultures grown on 5.5 mM glucose formed five domes per microscopic field while those exposed to elevated glucose concentrations (11.0 mM to 27.5 mM) formed only two to three domes per field. The areas of the domes formed by the cells grown on elevated glucose concentrations were reduced as compared to those formed on 5.5 mM glucose. An analysis of the electrical properties of cells grown on elevated glucose concentrations by Ussing chamber technique disclosed a marked reduction in potential difference, short circuit current, and resistance compared to cells grown on 5.5 mM glucose. Routine ultrastructural analysis disclosed that cells grown on elevated glucose concentrations appeared to have fewer tight junction complexes. Further examination utilizing freeze fracture methodology demonstrated that cells grown on elevated glucose concentrations averaged two to three sealing strands per junction as compared to an average of five sealing strands for cells grown on 5.5 mM glucose. The cells grown on elevated glucose concentrations were also noted to possess a greater number of gap junctions. These results demonstrate that elevated glucose concentrations can alter the paracellular route, and possibly the transcellular route, of transport regulation in cultured human proximal tubule cells.

Action Potentials↗
PubMed1988

Electrophysiology and ultrastructure of cultured human proximal tubule cells.

The present study was undertaken to determine if cultures of human proximal tubule cells would retain in vivo properties inherent to this segment in the intact nephron. Ussing chamber studies demonstrated that these cultured cells generated transepithelial potential differences of approximately -2.0 mV and resistances of 0.310 K omega.cm2, supporting the concept that the proximal tubule is a "leaky" epithelium. The electrical properties did not change when the cells were exposed to amiloride (10(-4) M), but did respond to acetazolamide (10(-4) M), consistent with responses known to occur in proximal tubules. Ultrastructural analysis of these cells demonstrated features indicative of proximal tubule cells. When grown on permeable supports, where apical and basolateral growth medium compartments were maintained separate from each other, the cells were noted to undergo increased differentiation with morphological evidence of cell polarity. Freeze fracture analysis demonstrated well-formed tight junction strands and segregation of unique numbers of intramembranous particles in apical, lateral, and basal membranes. The replicas also demonstrated the presence of aggregates though to represent gap junctions, structures which occur exclusively in the proximal segment of the human nephron. These observations provide evidence that this human cell culture model originates from the human proximal tubule and retains, in culture, many of the properties associated with proximal tubule cell function and structure in vivo.

Cells, Cultured↗
PubMed1984

Effect of hyperbaric oxygen on 2-deoxy-D-glucose and L-glutamate transport in rat cortical synaptosomes.

Initial velocities of uptake of L-glutamic acid and 2-deoxy-D-glucose (2-Dg) have been measured in cortical synaptosomes from rats which had been exposed to oxygen at high pressure (OHP) and compared to similar measurements in normobaric controls. Exposure to OHP had no significant effect on glutamate uptake at any combination of sodium and glutamate used. In contrast, OHP reduced 2-Dg uptake by an average of 17.5%. Although Kt was little affected, OHP exposure reduced apparent maximal transport capacity by 15%. Since hyperbaria with normal pO2 had no significant effect on uptake, the effect of OHP is an oxygen effect, rather than a pressure effect. The effects of OHP on uptake do not parallel the effects of age; glutamate transport capacity was reduced in aged animals, while 2-Dg transport was unaffected.

Aging↗
PubMed1983

Effect of hyperbaric oxygen on GABA transport in rat brain synaptosomes.

Initial velocities of uptake of GABA have been measured in rat brain synaptosomes from animals which had been exposed to oxygen at high pressure (OHP) and compared to similar measurements in normobaric controls. For hypothalamus, no changes in GABA uptake occurred subsequent to exposure to OHP. For cortical synaptosomes, however, exposure to OHP resulted in a decreased velocity of GABA uptake at all combinations of [Na] and [GABA] used. The OHP data were found to fit the same transport model as found previously for control data. Thus, OHP exposure did not alter the basic mechanism by which sodium and GABA interact with the carrier in the process of transport. However, the constants which quantitate the model were changed by OHP exposure. As a consequence, the several kinetic parameters which are calculated from the model change in the OHP animals. These kinetic parameters are compared to similar calculations for both normobaric control animals and normobaric aged animals. Although the effects of OHP do not precisely parallel the effects of aging, the alterations in kinetic parameters are in several ways similar in the aged and OHP animals.

Aging↗
PubMed1983

Cardiac pacing under hyperbaric conditions.

Temporary external pacemakers have been reported to fail under hyperbaric conditions. In this study we investigated cardiac pacing under hyperbaric conditions. Permanent hermetically sealed pacemakers were found to function well under hyperbaric conditions, while several models of temporary external pacemakers failed. The electrical characteristics of pacing leads did not change under hyperbaric conditions. External pacing under hyperbaric conditions may be accomplished safely by using a permanent pacemaker attached to the patient's temporary external leads.

Animals↗
PubMed1983

The effects of spinal cord injury on somatosensory evoked potentials produced by interactions between afferent pathways.

The purpose of the present study was to determine the utility of somatosensory evoked potentials (SEPs) produced by interaction between afferent pathways for spinal cord injury evaluation. Interaction was measured as alterations in SEP configuration compared to controls. Monkeys anesthetized with N2O were used. Stimulus intensities were sufficient to excite all nerve fibers. The conditioning stimulus (CS) was applied to the left peroneal nerve and test stimulus (TS) to the left radial nerve. CS-TS intervals were 100 msec in duration. SEPs were recorded from primary cortical receiving area for the forelimb. Different surgical lesions were made at spinal cord level T3-T4. Amplitudes of TS-produced-SEPs remained unchanged postlesion. CS-produced-SEPs were found to be dependent upon the integrity of anterolateral column pathways. Accentuated interaction was observed following dorsal column ablation. Interaction was slightly enhanced after left hemisection but diminished after right hemisection or central cord lesion. Interaction between spatially separate afferent inputs as measured by SEP alteration was determined to be a sensitive indicator of spinal cord injury.

Afferent Pathways↗
PubMed1983

Far-field potentials as a method of monitoring acute and chronic spinal cord injury.

Far-field potentials (FFPs) were studied in monkeys to determine the utility of such responses in evaluating acute and chronic spinal cord injury. Monkeys (Macaca fascicularis) were anesthetized with 70% N2O 30% O2, immobilized with pancuronium bromide, and maintained on a respirator. Spinal cord transections were made at level T3-T4 and included bilateral dorsal columns or anterolateral columns, right or left hemisection, or central cord lesions. Percutaneous stimulation of both posterior tibial nerves was performed at a frequency of 3 Hz using 3-4 mA for 0.3 msec duration. Potentials were recorded from chronically implanted epidural electrodes (right ear reference) through a 300-3,000 Hz band pass filter. Each far-field potential represents the average of 256 individual responses recorded for a duration of 25 msec before and after cord lesion for up to 8 weeks. Seven reproducible components in the far-field potential could be identified. Following dorsal column transection all components were reduced in amplitude. After anterolateral column transection only latencies were altered. Right or left hemisections caused both attenuation of component amplitudes and latency alteration. Central cord lesions resulted in no detectable amplitude or latency disturbances. Control records likewise showed no changes. No major alterations, following day 1 posttransection, were observed, attesting to the relative stability of far-field potentials over long periods of time. Far-field potentials therefore may be useful in monitoring spinal cord injury.

Animals↗
PubMed1982

Classification of somatic evoked potentials through maximum entropy spectral analysis.

Maximum entropy (ME) spectra are currently considered to be superior to spectra calculated by means of Fast Fourier Transforms (FFT) because the former offer higher resolution. However, in terms of classification of somatic evoked potentials (SEPs), FFT spectra are found to be better than ME spectra. An even better set of parameters for discriminating SEPs is the set of reflection coefficients derived in the process of calculating the ME spectra. They permit separation of SEPs obtained from monkeys with dorsal column lesion from SEPs obtained from normal monkeys, as well as distinguishing between SEPs obtained from large nerve fiber stimulation and SEPs from stimulation of all nerve fibers.

Animals↗
PubMed1980

Effects of spinal cord lesions on somatic evoked potentials altered by interactions between afferent inputs.

In cats anesthetized with alpha-chloralose, somatic evoked potentials (SEP) were recorded in response to electrical stimulation of surgically isolated peripheral nerves. Selected surgical lesions were made at T9-L1 spinal cord and were histologically verified. Two stimulus magnitudes were used to activate peripheral nerves, one only exciting the large fibers and another exciting the small fibers as well. Control SEPs were recorded in response to stimulation of both large and small fibers of the radial nerve. The later components (latencies greater than 40 msec) of this SEP were suppressed when evoked 100 msec after application of a conditioning stimulus (CS) to the large fibers of either peroneal nerve. Bilateral transection of the dorsal columns and spinocervical tracts eliminates these effects. Increasing the CS intensity to include small diameter fibers again resulted in reduction of the later components of the SEP. This interaction was largely eliminated if the transection was extended to include mid-lateral cord tracts. These results suggest that the SEP can be influenced by small fiber afferent activity conducted in mid-ventrolateral spinal cord in the absence of the dorsal columns and spinocervical tracts. Alterations in the forelimb-evoked SEP by a conditioning hindlimb stimulus is a sensitive indicator of spinal cord integrity. This method may be used to assess whether low spinal injury spares ventrolateral columns.

Afferent Pathways↗
PubMed1980

The effects of low spinal injury on the latencies of cortical evoked responses from forelimb stimulation.

A previous report showed that following spinal cord transaction well below the C7 level in cats, later components of the cortical somatic evoked potential (SEP) (40 msec or longer) produced in response to median or radial nerve stimulation were abnormal (Katz et al., 1977). Evidence presented here shows that early components of the radial nerve SEP are also altered following spinal cord transection. Latencies of both early and late components were increased as higher functional transections of the spinal cord were made. This monotonic increase in latency of the primary components supports the hypothesis that the results may be due to increasing loss of excitatory input. Correlation of latency change with level of injury may serve as a useful diagnostic tool.

Animals↗