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Biomedical subjects

D O Smith

Publications and source records attributed to D O Smith.

At least 19 recordsLinked to original sources
PubMed1992

Calcium currents in rat motor nerve terminals.

Ca2+ currents in response to an action potential were recorded extracellularly under non-voltage clamped conditions from rat motor nerve terminals. The Ca2+ current was blocked by Cd2+, Co2+, and Ni2+. A residual component that could not be blocked by inorganic cations was inhibited completely by tetrodotoxin (TTX). The Ca2+ current was also moderately sensitive to the N- and L-type Ca2+ channel-blocker omega-conotoxin but was insensitive to the L-type channel-specific dihydropyridines. When a fraction of the terminal K+ currents was blocked by 10 mM tetraethylammonium (TEA), the Ca2+ current duration decreased only slightly as stimulation frequency increased from 0.5 to 20 Hz. When K+ currents were blocked by TEA plus 3,4-diaminopyridine (250 microM) though, the Ca2+ current duration decreased from greater than 70 ms to 8-10 ms as stimulation frequency increased from 0.5 to 20 Hz. Recovery of the duration following 20-Hz stimulation occurred faster during subsequent stimulation at 0.5 Hz than at 2 Hz. ATP and ACh inhibit Ca2+ currents at stimulation frequencies ranging from 0.5 to 20 Hz; however, when the purinergic and cholinergic autoreceptors are blocked by theophylline (100 microM) and pirenzepine (3 microM), respectively, the frequency-induced decrease in current duration persisted. Thus, motor nerve terminal Ca2+ current duration is determined by stimulus repetition frequency; this appears to involve intracellular Ca2+ accumulation, although effects secondary to variability in the time course of changes in terminal membrane potentials cannot be ruled out.

Acetylcholine↗
PubMed1992

Routes of acetylcholine leakage from cytosolic and vesicular compartments of rat motor nerve terminals.

Acetylcholine efflux at the rat neuromuscular junction was assayed following blockage of ACh transport into synaptic vesicles by 2-(4-phenylpiperidino) cyclohexanol (AH5183). [2H4]Choline was used as a labeled precursor. AH5183 completely blocked ACh efflux from the cytosolic compartment but had comparatively less effect on release from the unlabeled vesicular pool. Tissue [2H4]ACh levels increased after AH5183 addition due to cytosolic ACh retention. Thus, ACh in the non-vesicular pool (calculated to be 34% of the total ACh) may efflux solely via the AH5183-sensitive ACh transporter inserted into the terminal membrane. ACh released from the vesicular fraction was about 100-fold more than could be accounted for by miniature end-plate potentials; possible causes of this overestimate are discussed.

Acetylcholine↗
PubMed1991

Adenosine derived from hydrolysis of presynaptically released ATP inhibits neuromuscular transmission in the rat.

It has been established that ATP is released from motor nerve terminals and that exogenous ATP depresses end-plate potential (e.p.p.) amplitudes. This study assessed whether presynaptically released ATP reduced e.p.p.s. E.p.p.s in the rat extensor digitorum longus muscle were depressed by exogenous ATP and adenosine. If ATP hydrolysis to adenoisine was blocked, however, ATP had no effect. Addition of theophylline increased e.p.p. amplitude due to removal of the depressant effect caused by ATP contained in the quantal release. This inhibition was absent when the rate of release was reduced by high Mg2+. It is concluded that e.p.p. inhibition is mediated by adenosine derived from presynaptically released ATP.

Adenosine↗
PubMed1991

Effect of water leaching the adhesion of composite resin to bleached and unbleached bovine enamel.

Standardized cylinders of light-cured composite resin were bonded to the ground labial enamel surface of bovine incisor teeth that had been immersed in double-distilled water for 7 days after having been (a) immersed in hydrogen peroxide for 5, 30, or 60 min, then etched for 60 s with 37% phosphoric acid; (b) immersed in saline for 5, 30, or 60 min, then etched for 60 s with 37% phosphoric acid; (c) etched with 37% phosphoric acid for 60 s, then immersed in hydrogen peroxide for 5, 30, or 60 min; or (d) etched with 37% phosphoric acid for 60 s, then immersed in saline for 5, 30, or 60 min. The enamel surface was washed with water for 1 min and dried with compressed air for 30 s prior to applying the resin. The tooth and applied resin were stored in water at 37 degrees C for 1 day prior to shear and tensile testing. A total of 192 specimens was used, 8 for each enamel preparation mode, for each time period, and for each test. Test values were tabulated and statistically analyzed. Analysis of variance revealed significantly higher bond strength values (p less than 0.005) for hydrogen peroxide-treated as compared with saline-treated specimens. A significant interaction was also noted between test solution and etching order. Scanning electron microscopic examination of failed shear- and tensile-tested specimens revealed no significant solution-related differences in the fracture pattern or the resin quality.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1991

Artery anatomy and tortuosity in the distal finger.

The arterial architecture in the finger distal to the proximal interphalangeal joint was studied in sixty-seven cadaver fingers with the aid of an operating microscope. The course, frequency, location, and diameter of the dorsal nail fold artery and its anastomosis was recorded. Similar measurements were performed for the palmar anastomosis. The frequency of arterial tortuosity in the digital artery was compiled and a classification of its morphology devised. The characteristic of arterial tortuosity provides a degree of protection to these essential structures. Failure to recognize this facet of arterial anatomy may be one more factor contributing to our inability to successfully revascularize the distal finger in certain patients.

Arteries↗
PubMed1991

The distal venous anatomy of the finger.

An exhaustive anatomic dissection of all of the veins of the finger distal to the proximal interphalangeal joint was done. More than 3200 segments of veins were individually dissected out, measured, and recorded. From this survey new schematic diagrams have been drawn emphasizing the pertinent venous anatomy at the proximal, distal interphalangeal joints and eponychial levels. Suggestions are made for regions that are apt to have the largest vessels available for anastomosis.

Cadaver↗
PubMed1991

Digital artery tortuosity and elasticity: a biomechanical study.

The gross structure of the digital artery distal to the proximal interphalangeal joint is significantly different from its proximal portion. Previous research in this laboratory has revealed that over half of all fingers exhibit marked tortuosity of this artery in juxtaposition to the distal interphalangeal joint. Any structure with a large amount of bending will have the properties of a spring. An understanding of these properties may help in creating tension-free anastomoses during finger tip replantation. The elastic strength and energy storage capacities of the distal digital artery were measured in 26 cadaver arteries.

Arteries↗
PubMed1991

Autoreceptor-mediated purinergic and cholinergic inhibition of motor nerve terminal calcium currents in the rat.

1. After blocking K+ currents with 10 mM-tetraethylammonium (TEA) or TEA plus 250 microM-3,4-diaminopyridine (3,4-DAP). motor nerve terminal Ca2+ currents were recorded using focal extracellular electrodes. Two transmitters released from the terminal. ATP and acetylcholine (ACh), were then applied, and the effects on the nerve terminal Ca2+ current were measured. 2. ATP (50 microM) reduced the Ca2+ current by 34%, but this action is prevented when hydrolysis to adenosine is blocked by alpha,beta-methyladenosine 5'-diphosphate (200 microM). Thus, inhibition by ATP presumably occurs subsequent to ATP hydrolysis to adenosine. 3. Adenosine (50 microM) inhibited the terminal Ca2+ current by 29%. This was mimicked by the adenosine analogue L-phenylisopropyl adenosine (L-PIA) and blocked by theophylline (100 microM), which antagonizes adenosine receptors at micromolar concentrations. 4. ACh (100 microM) or the anticholinesterase methane sulphonyl fluoride (MSF; 1 mM) also depressed the terminal Ca2+ current. This response was mimicked by muscarine (100 microM) and antagonized by atropine (100 microM) or pirenzipine (4 microM), which is generally specific for M1 receptors. 5. Addition of Ba2+, which blocks adenosine-mediated K+ currents, had no effect on the inhibitory effects of either adenosine or ACh; similarly, neither adenosine nor ACh in the bath affected K+ current records obtained after blocking all inward currents with 10 mM-Co2+ and focal application of tetrodotoxin. 6. Incubation of the muscle for 4 h in pertussis toxin (10(-5) g ml-1) eliminated both adenosine- and ACh-induced inhibition of the terminal Ca2+ current. This result indicates the possible involvement of a G protein in the transduction of the feedback pathway. 7. Neither cyclic AMP analogues, the adenylate cyclase activator forskolin (10 microM), the phorbol ester phorbol 12-myristate 13-acetate (PMA; 3 microM) nor the diacylglycerol analogue 1,2-oleoylacetylglycerol (OAG; 3 microM) had any effect on adenosine- or ACh-induced depression of the terminal Ca2+ current. Therefore, pathways involving these particular second messengers are most probably not involved. 8. The effects of adenosine and ACh are non-additive. 9. These results indicate that ATP and ACh, which are released during exocytosis, may inhibit their own release through attenuation of the terminal Ca2+ current via autoreceptors coupled to a G protein.

Acetylcholine↗
PubMed1991

Sources of adenosine released during neuromuscular transmission in the rat.

1. The levels of adenine nucleotides and adenosine which accumulate in the neuromuscular junction during nerve stimulation of the rat extensor digitorum longus (EDL) muscle were assayed biochemically. The sources were also determined by the use of different inhibitors. 2. ATP and total adenine nucleotide release increased as stimulation frequency increased, consistent with previous evidence indicating ATP release from presynaptic sources. 3. Adenosine levels also increased during nerve stimulation. However, accumulation decreased by 46-58% when muscle activation was blocked by the addition of d-tubocurarine (dTC). Adenosine levels also decreased by 40-59% when adenine nucleotide hydrolysis to adenosine was blocked by the addition of 1 mM-alpha,beta-methyladenosine 5'-diphosphate. Thus, approximately half of the extracellular adenosine is released from activated muscle while the other half is derived from adenine nucleotide hydrolysis. 4. Similar quantities of adenine nucleotide and acetylcholine (ACh) accumulated during nerve stimulation. With adenine nucleotide and ACh hydrolysis blocked by alpha,beta-methyladenosine 5'-diphosphate and eserine, respectively, the calculated amounts of adenine nucleotide and ACh released were 1.2 x 10(-16) and 1.5 x 10(-16) mol (stimulus impulse)-1 endplate-1. 5. AH5183 (vesamicol), which blocks ACh release, reduced extracellular ACh and adenine nucleotide accumulation by 40 and 45%, respectively. It did not affect adenosine release from the activated muscle. 6. Theophylline (100 microM), which blocks adenosine receptors, caused ATP accumulation to increase by 38%; extracellular levels of adenosine derived from adenine nucleotide hydrolysis also increased by 17%. These results are consistent with the presence of adenosine-mediated inhibition of adenine nucleotide release. 7. It is concluded that adenine nucleotides (presumably in the form of ATP) and ACh are released jointly, and that ATP is hydrolysed fairly rapidly to adenosine. Adenosine resulting from ATP hydrolysis accounts for about half of the extracellular adenosine accumulating during nerve stimulation, while the other half is released directly by the underlying muscle.

Acetylcholine↗
PubMed1991

Adenosine 5'-triphosphate increases acetylcholine channel opening frequency in rat skeletal muscle.

1. The effects of extracellular adenosine 5'-triphosphate (ATP) on the acetylcholine (ACh) channel opening activity was studied in dissociated rat skeletal muscle cells using patch-clamp recording techniques in cell-attached configuration. 2. With 10 microM-ATP in the recording pipette, the spontaneous opening frequency on the the alpha-bungarotoxin-sensitive ACh channel increased significantly from 0.3 to 4.7 s-1, although the opening frequency was not as high as that activated by very low (0.4 microM) ACh concentrations (64 s-1). 3. Spontaneous ACh channel openings, and ATP-associated and ACh-activated channel openings had similar single-channel conductances, 55, 59 and 56 pS, respectively. 4. ATP-associated events and spontaneous ACh channel opening events had similar mean channel open durations (0.6 ms); however, these values were considerably shorter than the duration of ACh-activated events (2 ms). 5. Pre-treatment with alpha-bungarotoxin (100 nM) blocked spontaneous ACh channel openings, ATP-associated openings and ACh-activated openings. 6. When delivered through a separate drug pipette after the formation of a gigaseal, ATP increased ACh-activated single-channel open probability in a dose-dependent fashion. 7. The increase in channel open probability was due primarily to the increase in channel opening frequency. ATP did not significantly alter the mean channel open duration or the single-channel conductance. 8. The ATP analogue adenosine-5'-O-(3-thiotriphosphate) (ATP-gamma-S) also enhanced ACh-activated channel open probability with relatively less potency. ADP, AMP and adenosine (up to 1 mM) did not significantly increase ACh channel open probability. 9. It is concluded that ATP in the micromolar range facilitates both spontaneous and agonist-activated ACh channel opening. The facilitation is due to ATP itself and not to products of ATP hydrolysis. The facilitatory actions of ATP on ACh channels are manifested by the increase in the channel opening frequency, and they may be mediated by an intracellular second messenger.

Acetylcholine↗
PubMed1991

Glutamate-activated channels in adult rat ventral spinal cord cells.

1. Currents in response to rapid application of glutamate and its agonists were studied in cells dissociated from the ventral spinal cord of adult rats. 2. Glutamate activated an inward current that desensitized in less than 15 ms. 3. Responses to quisqualate and to DL-alpha-amino-3-hydroxy-5-methyl-isoxeazolepropionic acid (AMPA) also desensitized with time constants ranging from 7 to 18 ms in whole cell configuration and from 3.4 to 4.3 ms in outside-out configuration. Desensitization rate was independent of membrane potential. Single-channel conductance was 12 pS. 4. Currents in response to N-methyl-D-aspartate activation also desensitized; the time constants ranged from 15 to 50 ms. Single-channel conductance was 23 pS. 5. Kainate responses did not desensitize appreciably. Single-channel conductance was 17 pS. 6. These data obtained from adult cells are similar to values reported for cultured embryonic and neonatal neurons, indicating minimal postnatal changes in these aspects of glutamate receptors.

2-Amino-5-phosphonovalerate↗
PubMed1991

Desensitization and resensitization rates of glutamate-activated channels may regulate motoneuron excitability.

1. Single-channel properties of desensitizing glutamate-activated channels were analyzed in outside-out patch-clamp recordings from a motoneuron-enriched cell fraction from embryonic chick. A piezo-driven device was used to achieve fast solution exchange at the electrode tip, resulting in maximum activation within 2 ms. 2. Quisqualate/AMPA receptors, with a 13-pS conductance, desensitized rapidly; the desensitization rate depended on agonist concentration but not on membrane potential. When quisqualate was applied slowly, the quisqualate-activated channels desensitized without prior channel opening, indicating desensitization from the closed state. After a 10-ms refractory period, resensitization of all channels required up to 300 ms; resensitization rate did not depend on the duration of the preceding quisqualate application. 3. At agonist concentrations less than or equal to 1 mM, kainate receptors, with a 20-pS conductance, did not desensitize. At kainate concentrations greater than or equal to 1 mM, though, kainate receptors desensitized to a low steady-state conductance within approximately 200 ms. Resensitization of all channels required as long as 3 s, which could render kainate receptors inexcitable during high-frequency activation. 4. Desensitization rates of whole-cell currents were similar to those observed in outside-out mode. Glutamate- and quisqualate-activated responses were similar, suggesting that the rapidly desensitizing quisqualate-sensitive receptor type may dominate the kinetics of whole-cell excitatory postsynaptic currents (EPSCs) in this preparation. 5. It may be concluded that the efficacy of glutamate-mediated synaptic transmission is modulated by differences in the rates of desensitization and resensitization.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1990

Age-related increase in soluble and cell surface-associated neurite-outgrowth factors from rat muscle.

While the number of nerve terminals per endplate decreases with age in the rat extensor digitorum longus (EDL) muscle, the number of endplates exhibiting ultraterminal sprouting, characteristic of denervation, increases. To determine if these changes associated with aging are accompanied by alterations in the production of muscle-derived neurite-outgrowth factors, we examined the effects of soluble and cell surface-associated components from innervated and denervated 10- and 25-month rat EDL muscles on a motoneuron-enriched fraction of embryonic chick spinal cord cells in vitro. Cells were cultured for 72 h with muscle extract or on muscle cross-sections. While soluble components of the extract affected initiation of neurite outgrowth, muscle cell surface-associated molecules influenced neurite elongation. Both muscle extract and muscle cross-sections from 10-month denervated animals were more effective in promoting neurite outgrowth than 10-month innervated muscle. There was no difference between 25-month innervated and 25-month denervated muscle. However, 25-month innervated and denervated muscles were significantly more effective in promoting neurite outgrowth than 10-month innervated muscle, but not different from 10-month denervated muscle. These results suggest that an age-related increase in muscle-derived soluble and cell surface-associated neurite-outgrowth factors may contribute to denervation-like morphological changes associated with aging at the neuromuscular junction.

Aging↗
PubMed1990

Changes in acetylcholine receptor distribution and binding properties at the neuromuscular junction during aging.

Junctional and extrajunctional acetylcholine receptors were characterized in diaphragm muscle obtained from mature adult and aged rats. Rhodamine-conjugated alpha-bungarotoxin was used to visualize receptor localization. At this level of resolution, there were no major changes in receptor distribution, and nerve terminals were consistently associated with receptors and vice versa. Specific binding characteristics were assayed by measuring 125I-alpha-bungarotoxin binding. Maximal binding to intact junctional and extrajunctional tissue samples was greater in the older rats. The association rate constant in minced tissue decreased in the older animals. Retardation of the initial rate of toxin binding by d-tubocurarine was described by a two-component nonlinear Hofstee plot; values of Ki were about the same for both age groups, but there was a significant shift towards the low-affinity values in the aged rats. Miniature end-plate currents (m.e.p.c.s.) were recorded under voltage-clamp conditions before and after AChE inhibition. When AChE activity was inhibited m.e.p.c. amplitudes and decay time-constants increased in both age groups. The magnitude of these increases was larger in the older animals. Inhibition of AChE did not affect mean channel open time, which was estimated from spectral analyses of ACH-induced membrane noise. Lipid composition was assayed in whole muscle and isolated sarcolemma. Muscle cholesterol concentration rose 15-20 percent, but phospholipid concentrations were maintained. However, neither cholesterol, phospholipid levels, nor membrane fluidity changed significantly with age in isolated sarcolemmal membrane fractions. These data indicate that the numbers of junctional and extrajunctional receptors increase with age. In the junctional region, this is quite likely due to an expanded field of receptors and not an increased density. This is associated with an increased fraction of receptors with lower binding affinity during aging. These changes apparently are not caused by major changes in membrane fluidity or lipid composition.

Aging↗
PubMed1990

Acetylcholine synthesis and release in the extensor digitorum longus muscle of mature and aged rats.

Uptake of labeled choline and its incorporation into acetylcholine (ACh) were assayed at the neuromuscular junction of the extensor digitorum longus (EDL) muscle of rats aged 11 (mature adult) and 27 (aged) months. Under resting conditions, there were no significant differences in muscle ACh or choline levels. Following a 1-h incubation in labeled choline, however, tissue from the younger rats contained significantly greater amounts of labeled choline and labeled ACh; the specific activities of ACh and choline were nearly 10-fold higher in the 11-month-old animals, indicating reduced uptake of labeled choline in the older animals. ACh and choline efflux rates under resting conditions did not change with age, indicating an uncoupling of exogenous choline uptake and ACh efflux in EDL during aging. During nerve stimulation (1 Hz), the amount of labeled choline incorporated into ACh was 150% greater in the aged animals. The specific activity of ACh released during stimulation was correspondingly greater in the 27-month-old animals, although total ACh released did not change appreciably with age. There were no age-related differences in choline acetyltransferase activity. Contrasting results were obtained from diaphragm in previous studies; the linkage between choline uptake and ACh efflux was maintained during rest and stimulation in the diaphragm. Hypothetically, these differences between EDL and diaphragm may be related to their diverse activation patterns: EDL is recruited much less frequently and less regularly than diaphragm, a continually active vital muscle.

Acetylcholine↗
PubMed1989

Cholesterol conservation in skeletal muscle associated with age- and denervation-related atrophy.

The lipid composition of muscles with age- and denervation-atrophy was assayed in whole muscle and isolated sarcolemma of rats aged 10 and 25 months. Although muscle mass decreased at least 17% during aging, muscle cholesterol concentration rose 15-20%. However, phospholipid concentrations were maintained; therefore, the cholesterol-to-phospholipid ratio increased during aging. Plasma cholesterol levels also rose 35%, but this could account for only about 10% of the age-related difference in muscle cholesterol. Likewise, following denervation (7 days) muscle mass decreased by at least 30%, but muscle cholesterol-to-phospholipid ratio increased; the magnitude of the denervation-induced response was unaffected by aging. To localize the source of cholesterol deposition during aging, these assays were repeated on isolated sarcolemma, sarcoplasmic reticulum, and mitochondria membrane fractions. Neither cholesterol nor phospholipid levels changed significantly with age in any of these major membrane systems. Furthermore, sarcolemmal fluidity, which depends on cholesterol content, did not vary significantly with age. At this level of resolution, it thus appears that skeletal muscle membrane phospholipid composition and fluidity do not change appreciably with age. Elevated cholesterol-to-phospholipid ratios detected in whole muscle may be due to cholesterol deposition in non-myofiber locations.

Aging↗