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Biomedical subjects

D L Wilson

Publications and source records attributed to D L Wilson.

At least 109 records · Page 6Linked to original sources
PubMed1985

Single channel and whole cell sodium currents in heart cells.

We studied TTX-sensitive Na channels in dissociated single ventricular cells from neonatal rats using the patch clamp method for single channel and whole cell recording. In both cases, slowly inactivating or window currents were observed that decayed in a biexponential fashion. Customary models of Na current kinetics such as the Hodgkin-Huxley model attribute activation to a process that is much faster than inactivation. The model of Aldrich, Corey and Stevens(1), says that inactivation is fast and final and activation is dispersed. We found activation too associated, deactivation too quick, and reopenings too frequent to accept this model for cardiac Na channels. We also found that the predominant set of single Na channels had one open state and two inactivated states. Rarely, a second set of Na channels having about 2/3 the conductance and mean open time of the predominant set was found.

Action Potentials↗
PubMed1984

Are different proteins synthesized in distinct domains in a neuron?

Are different messenger RNA species translated in distinct, limited domains within a cell? For the particular case of the giant R2 neuron from Aplysia californica an answer to this question is possible for the more abundantly synthesized proteins. After brief labeling with 35S-methionine, the R2 neuron soma was frozen and divided into two or three parts. The newly synthesized proteins were analyzed following two-dimensional polyacrylamide gel electrophoresis. No evidence for limited domains of synthesis for 26 abundantly synthesized polypeptides in the R2 neuron was found.

Animals↗
PubMed1984

Activation and inactivation of single calcium channels in snail neurons.

Activation and inactivation properties of Ca currents were investigated by studying the behavior of single Ca channels in snail neurons. The methods described in the previous paper were used. In addition, a zero-phase digital filter has been incorporated to improve the analysis of latencies to first opening, or waiting times. It was found that a decrease in the probability of single channel opening occurred with time. This was especially marked at 29 degrees C and paralleled the inactivation observed in macroscopic currents. The fact that a single channel was observed means that there is a significant amount of reopening from the "inactivated" state. Small depolarizations at 18 degrees C showed little inactivation. From these measurements, histograms of single channel open, closed, and waiting times were analyzed to estimate the rate constants of a three-state model of activation. Two serious discrepancies with the model were found. First, waiting time distributions at -20 mV were slower than those predicted by parameters obtained from an analysis of the single channel closed times. Second, it was shown that the time and the magnitude of the peak of the waiting time histogram were inconsistent with a three-state model. It is concluded that a minimum of four states are involved in activation. Some four-state models may be eliminated from further consideration. However, a comprehensive model of Ca channel kinetics must await further measurements.

Animals↗
PubMed1983

Recovery of Ca currents from inactivation: the roles of Ca influx, membrane potential, and cellular metabolism.

Ca currents were examined with regard to their recovery from inactivation. The experiments were done on isolated nerve cell bodies of Helix aspersa using a combined suction pipet , microelectrode method for voltage clamp, and internal perfusion. Ca currents were separated by suppressing K and Na currents. The time course of recovery was determined by applying a test pulse at intervals ranging from 1 msec to 20 sec after prepulses varying from 20 to 3000 msec in duration. Each pair of pulses was preceded by a control pulse to ensure that the Ca currents had recovered before the next test pair was applied. Ba and Ca currents were compared and the effects of intracellular perfusion with EGTA, ATP, and vanadate were examined. Ba currents recovered in two stages and this time course was well fit by a sum of two exponentials with amplitudes and time constants given by A1 and tau 1 for the fast component and A2 and tau 2 for the slow component. In Ba the time constants were unchanged when prepulse durations were prolonged from 70 to 700 msec, although the initial amplitudes A1 and A2, particularly A2, were increased. Comparable influxes of Ca during the prepulse caused much more inactivation, but interestingly the recovery occurred at the same rate. The time course of Ca current recovery was also fit by a sum of two exponentials, the time constants of which were both smaller than the time constants of Ba current recovery. However, the time constants of Ca current recovery were increased markedly when prepulse durations were prolonged. Increasing the extracellular Ca concentration had a similar effect. Increasing the Ba influx had no effect on the recovery time constants, and the Ba results are consistent with reversible inactivation gating of potential-dependent membrane Ca channels. The Ca results show that Ca influx enhances inactivation. Intracellular perfusion with EGTA resulted in less inactivation in the cast of Ca but it had no effect on Ba currents. Intracellular ATP increased the rate of recovery of Ca currents, and intracellular vanadate inhibited recovery. It is concluded that recovery of Ca channels depends upon both Ca influx and membrane potential and is modulated by agents which affect Ca metabolism.

Adenosine Triphosphate↗
PubMed1983

Interaction between calcium ions and surface charge as it relates to calcium currents.

Calcium ions affect the gating of Ca currents. Surface charge is involved but to what extent is unknown. We have examined this, using isolated nerve cell bodies of Helix aspersa and the combined microelectrode-suction pipette method for voltage-clamp and internal perfusion. We found that Ba and Sr currents produced by substitution of these ions for extracellular Ca ions are activated at less positive potentials than Ca currents. Mg ions do not permeate the Ca channel and changes in [Mg]o produce shifts in the activation-potential curves that are comparable to the effects of changes in [Ba]o or [Sr]o. Inactivation of Ba currents also occurs at less positive potentials. Perfusion intracellularly with EGTA reduced inactivation of Ca currents as a function of potential, but did not shift the inactivation-potential curve. Hence, Ca current-dependent inactivation which is blocked by intracellular EGTA probably does not involve a similar change of intracellular surface potential. The voltage shifts of activation and inactivation produced by extracellular divalent cations used singly or in mixtures can be described by the Gouy-Chapman theory for the diffuse double layer with binding (Gilbert & Ehrenstein, 1969; McLaughlin, Szabo & Eisenman, 1971). From the surface potential values and the Boltzman distribution, we have computed surface concentrations that predict the following experimental observations: 1) saturation of current-concentration relationships when surface potential is changing maximally; 2) the increase in peak current when Ca ions are replaced by Sr or Ba ions; and 3) the greater inhibitory effect of Mg on IBa than ICa. Theory indicates that surface charge cannot be screened completely even at 1 M [Mg]o and thus that Ca channel properties must be evaluated in the light of surface charge effects. For example, after correction for surface charge effects the relative permeabilities of Ca, Ba and Sr ions are equivalent. In the presence of Co ions, however, Ca ions are more permeable than Ba ions suggesting a channel binding site may be involved.

Animals↗
PubMed1983

The mechanical properties of human tibial trabecular bone as a function of metaphyseal location.

Experimental determination of the elastic modulus and ultimate strength of human tibial trabecular bone as a function of metaphyseal location is presented. A 1 cm cubic matrix with planes parallel to the subchondral plate was defined on five fresh frozen cadaver tibias. Approximately 400, 7 mm X 10 mm cylindrical bone plugs were cut from the locations defined by the matrix and tested in uniaxial compressive stress at a strain rate of 0.1%S-1. Results of the study indicate that the trabecular bone properties vary as much as two orders of magnitude from one location to another. As might be predicted from Wolff's law, and noted by previous investigators, concentrations of strength arise from the medial and lateral metaphyseal cortices toward the major medial and lateral contact regions. These results may be valuable for improved analytical modeling and optimal prosthetic design.

Aged↗
PubMed1983

Protein synthesis and rapid axonal transport during regrowth of dorsal root axons.

Damage to the sciatic nerve produces significant changes in the relative synthesis rates of some proteins in dorsal root ganglia and in the amounts of some fast axonally transported proteins in both the sciatic nerve and dorsal roots. We have now analyzed protein synthesis and axonal transport after cutting the other branch of dorsal root ganglia neurons, the dorsal roots. Two to three weeks after cutting the dorsal roots, [35S]methionine was used to label proteins in the dorsal root ganglia in vitro. Proteins synthesized in the dorsal root ganglia and transported along the sciatic nerve were analyzed on two-dimensional gels. All of the proteins previously observed to change after sciatic nerve damage were included in this study. No significant changes in proteins synthesized in dorsal root ganglia or rapidly transported along the sciatic nerve were detected. Axon regrowth from cut dorsal roots was observed by light and electron microscopy. Either the response to dorsal root damage is too small to be detected by our methods or changes in protein synthesis and fast axonal transport are not necessary for axon regrowth. When such changes do occur they may still aid in regrowth or be necessary for later stages in regeneration.

Animals↗
PubMed1983

A description of activation and conduction in calcium channels based on tail and turn-on current measurements in the snail.

Turn-on of Ca currents, or activation, was compared with turn-off, or deactivation. The experiments were done on nerve cell bodies of Helix aspersa separated by dissection, voltage-clamped and internally perfused using a combined suction pipette--micro-electrode method. Ca currents were isolated by suppression of Na and K currents. The turn-off or tail currents were large and fast; this required that the limitations of the voltage clamp be established. A second micro-electrode was inserted to determine temporal and spatial control of potential, and it was found that the cells were essentially equipotential within 60 microsec during the largest tail currents. Series resistance was less than 5 k omega as measured by a small-perturbation, pseudorandom noise-current signal and presented negligible error in the measurements. Activation was complicated by the presence of asymmetry currents which required evaluation. This was done after Co replacement for Ca. The asymmetry currents were sufficiently small for their contribution to the tail currents to be ignored. Addition of Cd to Ca solutions could not be used since relatively large inward tail currents persisted in the presence of Cd. Tail currents were fitted by sums of two or three exponentials; each was sensitive to Ca-channel blockers but only two were due to closure of Ca channels. The two faster components with time constants tau F and tau S, for fast and slow respectively, were produced by brief, 3.0 msec voltage pulses and were present in all cells. The third and slowest component with time constant tau VS, for very slow, activated much more slowly and was not always present. The amplitudes of tau F and tau S were reduced by cooling and were increased when Ca was replaced by Ba extracellularly or when the external Ca concentration was increased. Hence, these components were due to closure of Ca channels. The third component activated faster in Ba solution. When fully activated it had the same amplitude in either Ba or Ca solution despite the differences in amplitude of Ba and Ca currents during the voltage-clamp step. The amplitude of the third component was also not changed by increasing external Ca concentration; hence it was not due to closure of Ca channels. Cooling also had very little effect. The third component was abolished by Ca blockers, but it does not appear to be related to previously described Ca-activated currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Modification of a rapidly transported protein in regenerating nerve.

From 1 to 28 days after frog sciatic nerve damage, dorsal root ganglia were incubated with [35S] methionine, and the labeled, rapidly transported proteins at various points along the nerve were analyzed on two-dimensional gels. The results show a dramatic increase in the labeling of a protein, which we have designated as A25, only after the arrival of the rapidly transported proteins at regenerating nerve tips. This effect is first seen 3 to 5 days after injury. On gels from regenerating nerves, A25 appears as a series of intense spots with an apparent molecular weight of 70,000. A25 is retrogradely transported from the regenerating nerve tip regions. Since labeled A25 increases only after the rapidly transported proteins reach regions of nerve containing regenerating axons, we conclude that it most likely arises from post-translational modification of a transported protein. Various experiments were conducted to rule out alternative sources of A25 labeling at the nerve periphery.

Animals↗
PubMed1982

Prevalence of antibody to serogroups 1-4 of Legionella pneumophila: a seroepidemiologic study using the indirect hemagglutination test.

An indirect hemagglutination test was used to determine the prevalence of antibody to serogroups 1-4 of Legionella pneumophila in sera from 1200 apparently healthy Michigan residents. Serogroup 1 was the most prevalent; 71 (11.8%) of 600 sera collected during the winter months (January-April, 1980) and 131 (21.8%) of 600 sera collected during the summer period (July-September, 1980) had serogroup 1 titers. This seasonal difference was independent of sex and was statistically significant in four of six age groups studied. A trend toward decreasing prevalence in the 50-59 years and 60 years or older age groups was noted in the winter sample and was statistically significant in the summer study. Prevalence of antibody to serogroups 2, 3, and 4 was significantly lower, and was associated with serogroup 1 reactivity.

Adolescent↗
PubMed1982

On the identification of alpha- and beta-tubulin subunits.

Confusion appears to have arisen in the literature regarding the designation of alpha- and beta-tubulin in polyacrylamide gels. The presence or absence of 8 M-urea in sodium dodecyl sulfate (SDS) polyacrylamide gels leads to different patterns for unalkylated tubulin subunits (and other proteins), making difficult the designation of the alpha and beta subunits by original definition using electrophoretic mobility in the molecular weight dimension. The specific biochemical property of posttranslational tyrosylation of the alpha subunit has been used to identify further this subunit. Under all conditions tested, the beta subunit has been found to be more acidic than the alpha subunit, with isoelectric point differences that agree with theoretical and published values. If the tubulin subunits are reduced and alkylated, the beta subunit migrates more rapidly in SDS polyacrylamide gels, with or without urea present. However, unalkylated tubulin subunits can comigrate or even reverse their relative mobility if 8 M-urea-SDS polyacrylamide gels are used for subunit separation. The results also confirm the earlier reports that the post-translational tyrosylation of protein appears exclusively restricted to alpha-tubulin and can be demonstrated in an in vivo situation. In addition, the results suggest that only the alpha 2 subunit of tubulin is tyrosylated.

Animals↗
PubMed1981

Are axonally transported proteins released from sciatic nerves?

A recent report by Hines and Garwood claimed a significant release of axonally transported proteins from frog sciatic nerve into a surrounding solution. In the present study no significant release of axonally transported protein from frog sciatic nerves was detected with more stringent control for non-axonal sources of released protein.

Animals↗
PubMed1981

Protein synthesis and axonal transport during nerve regeneration.

Protein synthesis and axonal transport have been studied in regenerating peripheral nerves. Sciatic nerves of bullfrogs were unilaterally crushed or cut. The animals were killed 1, 2, or 4 weeks later, and 8th and 9th dorsal root ganglia removed together with sciatic nerves and dorsal roots. The ganglia were selectively labeled in vitro with [35S]-methionine. Labeled proteins, in dorsal root ganglia and rapidly transported to ligatures placed on the sciatic nerves and dorsal roots, were analyzed by two-dimensional polyacrylamide gel electrophoresis. Qualitative analysis of protein patterns revealed no totally new proteins synthesized or rapidly transported in regenerating nerves. However, quantitative comparison of regenerating and contralateral control nerves revealed significant differences in abundance for some of the proteins synthesized in dorsal root ganglia, and for a few of the rapidly transported proteins. Quantitative analysis of rapidly transported proteins in both the peripheral processes (spinal nerves) and central processes (dorsal roots) revealed similar changes despite the fact that the roots were undamaged. The overall lack of drastic changes seen in protein synthesis and transport suggests that the neuron in its program of normal maintenance synthesizes and supplies most of the materials required for axon regrowth.

Animals↗