Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Photometry”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,225 records · Page 68Linked to original sources
PubMedDate not supplied

Deoxyribonucleic acid (DNA) content of morphologically different sperm types from normal and subfertile human males.

20 male patients (G2), affected by idiopathic oligozoospermia, and 10 normal fertile males (G1) were investigated. The DNA content of 50 Feulgen stained sperm heads per subject was determined, using single cell photometry. In a second step area, circumference, length, and width of the same heads were measured, using a semi-automatic image analysis system. Considering only morphologically normal heads, the mean DNA content is only slightly smaller in G2 than in G1. On the contrary, the DNA variation is strongly higher in G2 than in G1. Unfortunately, morphologically defect heads show an increased DNA variation, too. Thus, determining the DNA variation of a semen, containing many morphologically defect heads, a combined determination of the DNA content and head morphology is necessary. This can only be achieved by single cell cytophotometry, which is therefore superior to flow cytophotometry as regards this problem. Many heads with a strongly abnormal DNA content do not show any morphological abnormalities. These subcellular changes can only be detected by the determination of the DNA content.

DNA↗
PubMed2005

Diagnosing protan heterozygosity using the Medmont C-100 colour vision test.

BACKGROUND: A surprisingly high 15 per cent of women in Caucasian societies are carriers of the genes for abnormal colour vision but there is no clinical method to identify them. It has long been known that heterozygotes for the protan colour vision deficiencies can demonstrate a reduced luminous sensitivity to red light. This is known as Schmidt's sign, which is thought to arise from mosaicism (Lyonisation). The Medmont C-100 colour vision test measures relative spectral sensitivity using flicker photometry to differentiate protans and deutans. It should be able to diagnose Schmidt's sign. METHOD: We tested six known protan heterozygotes (four whose sons have a protan colour vision deficiency and two whose fathers are protan) with the Medmont C-100 test. RESULTS: All six heterozygotes made average settings of -1.75 or more negative at the Medmont C-100 test, settings which are at or beyond the boundary of the distribution of settings made by observers with normal colour vision. There have been two previous cases reported in the literature of protan heterozygotes, who made protan settings on the Medmont C-100 or its predecessor test, the OSCAR. We also tested six daughters of the known heterozygotes, 50 per cent of whom are likely to be heterozygotes. Four of the six (66 per cent) made protan settings on the Medmont C-100. The other two made normal 0.0 settings. CONCLUSION: We conclude that the Medmont C-100 can be used clinically to diagnose carriers of protan colour vision deficiency.

Color Perception Tests↗
PubMed1998

ADP and inositol trisphosphate evoke oscillations of a monovalent cation conductance in rat megakaryocytes.

1. A combination of conventional whole-cell patch clamp recordings and fura-2 fluorescence photometry was used to study the membrane currents during oscillations of intracellular Ca2+ concentration ([Ca2+]i) in single rat megakaryocytes. 2. At a holding potential of -60 mV, in NaCl external saline and KCl internal saline with low levels of Ca2+ buffering, 10 microM ADP evoked [Ca2+]i oscillations and simultaneous Ca2+-gated K+ currents at a frequency of 3-10 spikes min-1. A smaller inward current was also activated, with a time course that identified this component as the inositol 1,4, 5-trisphosphate (IP3)-activated monovalent cation current previously demonstrated in rat megakaryocytes. 3. Cs+ replacement of internal K+ combined with 100 nM external charybdotoxin (CTX) abolished the outward currents and revealed that an inward current was also transiently activated during each [Ca2+]i spike. This underlying conductance was permeable to Na+ and Cs+, but possessed little or no permeability to Cl- or divalent cations. 4. Intracellular dialysis with IP3 (5-50 microM) activated the monovalent cationic conductance prior to release of Ca2+ from intracellular stores. The [Ca2+]i increase was associated with a second phase of cationic current, implying that both IP3 and Ca2+ can activate this conductance. Buffering of [Ca2+]i with BAPTA abolished the second phase of current, leaving monophasic spikes of inward current, often occurring at regular intervals. 5. These data demonstrate that a monovalent cation current, which results in Na+ influx under normal ionic conditions, oscillates in response to ADP receptor stimulation due to activation by both IP3 and [Ca2+]i. This provides a route for long-term Na+ entry in the megakaryocyte following stimulation of receptors coupled to phospholipase C activation and may play a role in cell shape change.

Adenosine Diphosphate↗
PubMed2005

CFF thresholds: relation to macular pigment optical density.

PURPOSE: Only two small studies have evaluated the relation between individual differences in macular pigment (MP) levels and visual health prior to retinal disease. In this study, we assess the relation between MP and a general measure of visual health, the critical flicker fusion (CFF) threshold. METHODS: A total of 134 subjects were assessed. CFF values were determined psychophysically using a 570 nm, circular 1-degree test field centrally fixated. MP optical density was measured using flicker photometry and a 1-degree circular 458 nm test field centrally fixated. Personal characteristics were determined by questionnaire. RESULTS: Similar to past studies, we found a significant decline in CFF values with age (r = -0.56). There was a significant positive relationship (r = 0.30, p < 0.001) between MP density and CFF values that was independent of age. CONCLUSIONS: These results are consistent with a protective effect of MP on visual health across the lifespan.

Adolescent↗
PubMed2006

Visual performance in night-time driving conditions.

This paper introduces an experimental multitechnique method which was developed to establish a basis for a task performance-based mesopic photometry. This approach considers night-time driving by dividing visual performance into three visual tasks, of which achromatic threshold and reaction time are presented. The performance of both visual tasks decreased with decreasing luminance level from 1 to 0.01 cd m(-2), showing the strong effect of light level on visual performance in driving. The behaviour of the achromatic contrast threshold and reaction time for low-contrast targets was similar in terms of spectral effects, the strongest effects occurring at the lower mesopic levels. Both measures showed the Purkinje shift with decreasing luminance levels. The experimental data were used to calculate mesopic performance measures with the new mesopic model. The results imply that compared with V(lambda), spectral sensitivity in night-time driving can be better described with a mesopic model based on visual performance measures.

Adult↗
PubMed1995

Caffeine-evoked, calcium-sensitive membrane currents in rabbit aortic endothelial cells.

1. Single cell photometry and whole-cell patch clamp recording were used to study caffeine-induced intracellular Ca2+ signals and membrane currents, respectively, in endothelial cells freshly dissociated from rabbit aorta. 2. Caffeine (5 mM) evoked a transient increase in [Ca2+]i in fura-2-loaded endothelial cells. Pretreatment of cells with 10 microM ryanodine did not alter resting [Ca2+]i but irreversibly inhibited the caffeine-induced rise in [Ca2+]i. The caffeine-induced increase in [Ca2+]i was not attenuated by the removal of extracellular Ca2+ and did not stimulate the rate of Mn2+ quench of fura-2 fluorescence. 3. Bath application of caffeine evoked a dose- and voltage-dependent outward current. The rate of onset and amplitude of the caffeine-evoked outward current increased with higher caffeine concentrations and membrane depolarization. The relationship between caffeine-evoked current amplitude and membrane potential was non linear, suggesting that the channels underlying the current are voltage-sensitive. 4. In the absence of extracellular Ca2+, the amplitude of the caffeine-evoked outward current was reduced by approximately 50% but the duration of the current was prolonged compared to that observed in the presence of external Ca2+. Ca(2+)-free external solutions produced an unexpected increase in both the frequency and amplitude of spontaneous transient outward currents (STOCs). 5. Inclusion of heparin (10 micrograms ml-1) in the patch pipette abolished the acetylcholine (ACh)-induced outward current but failed to inhibit either STOCs or the caffeine-evoked outward current in native endothelial cells. In the absence of extracellular Ca2+, heparin did not affect either STOCs or the caffeine-induced outward current. 6. Externally applied tetraethylammonium ions (TEA, 3-10mM) reversibly inhibited unitary Ca2+-activated K+ currents and STOCs in endothelial cells but failed to inhibit completely the outward current evoked by 20 mM caffeine.7. Bath application of 0.1 mM zinc ion (Zn2+), a chloride channel blocker, did not affect unitary currents or STOCs but reduced the amplitude of the caffeine-evoked current by >75% compared to control. Replacement of extracellular NaCl with Na gluconate also reduced the amplitude of the caffeine-induced outward current. Bath application of 0.1 mM Zn2+ and 10 mM TEA completely blocked the caffeine-evoked outward current in endothelial cells.8. Caffeine-induced Ca2+ release from intracellular stores evokes a transient rise in [Ca2+1, which is correlated with a large, transient outward current. The ionic dependence and inhibition of the caffeine sensitive current by TEA and Zn2+ suggests that Ca2+-activated K+ and Cl- conductances contribute to the caffeine response in rabbit aortic endothelial cells.

Animals↗
PubMed2000

Tissue kallikrein activity in pregnancy.

To determine tissue kallikrein (TK) activity in black African women with hypertensive disorders of pregnancy; 140 women were recruited and divided into the following groups: group A--35 preeclamptic women, group B--35 mild to moderate hypertensive pregnant women and group C--35 normotensive pregnant women, and group D--35 normotensive non-pregnant healthy women. The activity of tissue kallikrein was determined from a random untimed urine sample using a selective, synthetic chromogenic tripeptide substrate having the sequence H-D-Val-Leu-Arg-pNA (S-2266). Urinary sodium and potassium levels was determined by flame photometry. Tissue kallikrein activity was decreased in women with preeclampsia (1.54 +/- 0.95 vs 3.05 +/- 0.83 ngTK/microg protein; p < 0.0001) and mild to moderate hypertensive group (2.03 +/- 0.76 vs 3.05 +/- 0.83 ngTK/microg protein; p < 0.0001) compared with normotensive pregnant women. There was also a significant difference in tissue kallikrein activity between the pregnancy groups (1.54 +/- 0.95 vs 2.03 +/- 0.76 ngTK/microg protein; p < 0.001). No difference in tissue kallikrein activity was observed between normotensive pregnant and normotensive non-pregnant healthy women (3.05 +/- 0.83 vs 3.14 +/- 0.88 ngTK/microg protein; p = 0.51). There was no difference in the excretion of urinary sodium and potassium in pregnancy groups compared to normotensive pregnant group. Tissue kallikrein activity is decreased in hypertensive disorders of pregnancy.

Adult↗
PubMed2006

Transport of airborne particles within a room.

The objective of this study is to test a technique used to analyze contaminant transport in the wake of a bluff body under controlled experimental conditions for application to aerosol transport in a complex furnished room. Specifically, the hypothesis tested by our work is that the dispersion of contaminants in a room is related to the turbulence kinetic energy and length scale. This turbulence is, in turn, determined by the size and shape of furnishings within the room and by the ventilation characteristics. This approach was tested for indoor dispersion through computational fluid dynamics simulations and laboratory experiments. In each, 3 mum aerosols were released in a furnished room with varied contaminant release locations (at the inlet vent or under a desk). The realizable k approximately epsilon model was employed in the simulations, followed by a Lagrangian particle trajectory simulation used as input for an in-house FORTRAN code to compute aerosol concentration. For the experiments, concentrations were measured simultaneously at seven locations by laser photometry, and air velocity was measured using laser Doppler velocimetry. The results suggest that turbulent diffusion is a significant factor in contaminant residence time in a furnished room. This procedure was then expanded to develop a simplified correlation between contaminant residence time and the number of enclosing surfaces around a point containing the contaminant. Practical Implications The work presented here provides a methodology for relating local aerosol residence time to properties of room ventilation and furniture arrangement. This technique may be used to assess probable locations of high concentration by knowing only the particle release location, furniture configuration, inlet and outlet locations, and air speeds, which are all observable features. Applications of this method include development of 'rules of thumb' for first responders entering a room where an agent has been released and selection of sampler locations to monitor conditions in sensitive areas.

Air Movements↗
PubMed1982

Interaction between diphenolic laxatives and intestinal bacteria in vitro.

The ability of the laxative diphenols desacetylbisacodyl, oxyphenisatin, and phenolphthalein to inhibit growth and cause leakage of potassium ion from microbial cells in vitro was studied with 25 aerobic and 25 anaerobic bacterial strains. None of the aerobes, but some of the anaerobes showed growth inhibition. Potassium release assayed by flame photometry was observed in strains which showed growth inhibition, but also in other strains including anaerobes and aerobes. The highest antibacterial activity among the diphenols was observed with phenolphthalein and the least with desacetylbisacodyl; this relationship as noted for both growth inhibition and potassium release. Enzymatic hydrolysis of picosulphate to the free diphenol desacetylbisacodyl carried out by three strains of anaerobic bacteria was indicated by high pressure liquid chromatography.

Bacteria↗
PubMed1987

Studies on laxatives: biliary and urinary excretion in rats given danthron by intravenous infusion or gastric intubation.

Rats were infused with danthron (I) at doses of 0.48, 2.2 and 5.8 mumol/100 g body weight, or given 12 mumol/100 g with gastric tube. TLC of bile and urine demonstrated a number of metabolites, at both administration routes. These included I monosulphate (II) and -glucuronide (III), two other phase 2 metabolites which behaved as the corresponding diconjugates, and several phase 1 metabolites (IV) in conjugated form. IV as a group were estimated by photometry of hydrolysed samples, using I as a reference. Danthron conjugates as a group were determined in such samples by a specific method for I. Moreover, II and III were determined individually in unhydrolysed specimens. Following infusion, about 80% of the danthron conjugates in bile were excreted after 1 hour; the dose fractions found after 5 hours represented about 20%, 30%, and 40% at the low, intermediate and high dose level, respectively. The corresponding fractions in urine were 16%, 12% and 10%, giving rise to bile:urine excretion ratios of 1.3, 2.7 and 4.0, respectively. This change in excretion pattern was associated with changes in metabolite muster, which involved a decrease in the balance of IV:I conjugates, as well as an increase in III:II ratio. IV was more abundantly present in bile than in urine, and showed a more sustained excretion than the I conjugates. By intragastric administration, the cumulated excretion (bile + urine) of I conjugates were only 6%, 8% and 5% of dose, in three consecutive 6 hours' periods (0-6, 6-12 and 12-18 hours after dosing). The bile:urine excretion ratios seemed to decrease with time, as did the III:II ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Renal and cardiovascular effects of atrial natriuretic peptide in Wistar-Kyoto and spontaneously hypertensive rats during a chronic salt loading.

Spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats were maintained on tap water or 1.5% NaCl for 3 weeks. During the high sodium regime 24-h urinary sodium excretion increased 10-fold and the basal blood pressure increased in the SHR. After 3 weeks the rats received arterial (carotid artery), venous and bladder catheters (suprapubic). Saline was infused continuously and in conscious rats atrial natriuretic peptide (alpha-hANP) was administered as bolus injections (8 and 16 nmol kg-1) and the blood pressure and heart rate and the urinary excretions of sodium, potassium (flame photometry), noradrenaline and dopamine (HPLC) were followed at 5-min intervals. The administration of ANP caused a short-lasting blood pressure reduction, tachycardia, diuresis and increased urinary excretions of sodium, potassium, noradrenaline and dopamine. The blood pressure responses to ANP did not differ between the rat strains, irrespective of the diet. The natriuresis and diuresis to ANP was reduced in animals on a high sodium diet, especially in the SHR. This may be interpreted as a down-regulation of target organ responsiveness to ANP during a high sodium diet and the inappropriately large decrease in the responsiveness that was observed in the SHR may be related to increase in blood pressure during the high sodium diet.

Animals↗
PubMed1988

Characterization of the glucose-induced lowering of sodium in mouse pancreatic beta-cells.

The mechanisms for glucose regulation of the sodium content of the pancreatic beta-cells were examined using aggregates of cells prepared from ob/ob-mice of a local colony. Exposure to glucose rapidly resulted in a protracted lowering of the sodium content as estimated with integrating flame photometry. Sodium became decreased after addition of 1 mmol l-1 glucose, and this effect was maximal with 5 mmol l-1 of the sugar. The effects of low glucose concentrations on the sodium content could not be mimicked by the poorly metabolized 3-o-methyl-D-glucose, and it disappeared in the presence of the metabolic inhibitor antimycin A. The significance of the Na/K pump for maintaining low sodium was illustrated by a substantial increase of the element in the presence of ouabain. However, there was no indication that glucose-induced lowering of sodium reflected activation of this pump when measuring the ouabain-sensitive uptake of 86Rb+. Neither bumetanide nor the bromo derivatives of cyclic AMP or cyclic GMP modified the glucose action on the sodium content. In evaluating whether the effect of glucose was mimicked by other inhibitors of the K+ permeability it was observed that 100 mumol l-1 quinine, but not tolbutamide, decreased sodium. It is concluded that the beta-cell is exceptional among excitable cells in responding to its natural physiological stimulant (glucose) by reduction of sodium. Acting in this way glucose facilitates the removal of Ca2+ from the cytoplasm.

3-O-Methylglucose↗
PubMed1991

Comparison of distribution and photodynamic effects of di- and tetra-sulphonated aluminium phthalocyanines in normal rat colon.

We have previously reported photodynamic therapy of normal rat colon using aluminium sulphonated phthalocyanine (AISPc). In that study, the AISPc used was a mixture of phthalocyanines of different degrees of sulphonation. Phthalocyanines of defined degrees of sulphonation have recently become available and we compared the distribution of the di- and tetra-sulphonates (AIS2Pc and AIS4Pc) in rat colon and colon wall structures employing both chemical extraction and fluorescence photometry using a charge coupled device imaging system. Also, the photodynamic effects produced by these components in rat colon were compared at various times after photosensitization. After intravenous photosensitizer administration using equimolar doses, the concentration of AIS2Pc in colon fell off more rapidly with time than AIS4Pc. Differences were noted in the microscopic distribution of these compounds, with the di-sulphonate exhibiting peak fluorescence in colon wall structures by 1 h after photosensitization, while mucosal fluorescence with the tetra-sulphonate peaked at 5 h. Fluorescence was also lost from the colon wall much more slowly with the tetra-sulphonate, which tended to be retained in the submucosa. Maximum photosensitizing capability was seen at 1 h with AIS2Pc and no lesions could be produced with photodynamic therapy at 1 week, with up to 5.65 mumol/kg. With AIS4Pc (5.65 mumol/kg), while no lesions could be produced with light treatment at 1 h, photodynamic therapy at 1 week produced lesions only slightly smaller than those produced with treatment at 48 h (the time of maximum effect), and significant photosensitization was present at 2 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗
PubMed1995

Distribution of 5-aminolevulinic acid-induced porphyrins in noduloulcerative basal cell carcinoma.

Microscopic fluorescence photometry incorporating a light-sensitive thermo-electrically cooled charge-coupled device (CCD) camera was employed to investigate the fluorescence distribution of 5-aminolevulinic acid (ALA)-induced porphyrins in 22 patients with a total number of 52 noduloulcerative basal cell carcinomas (BCC) after topical ALA application with or without dimethylsulfoxide (DMSO)/ethylenediaminetetraacetic acid (EDTA) or after intravenous administration of ALA. Both localization patterns and amounts of ALA-induced porphyrins in the BCC were studied. The ALA-induced porphyrins were localized only in the superficial layers of the noduloulcerative BCC lesions after topical application of 20% ALA alone for 3 h. However, both the penetration of ALA into deep lesions and the production of the ALA-induced porphyrin fluorescence were increased after topical administration of 20% ALA and 20% DMSO/4% EDTA for 3 h. Prior treatment with 99% DMSO for 15 min further enhanced the ALA penetration into the BCC lesions after topical application of the ALA/DMSO/EDTA mixture and produced more ALA-induced porphyrins by a factor of about three compared with those treated with ALA alone. The penetration of ALA into the deep BCC lesions could also be increased by prolonging the time of topical application of 20% ALA/4% EDTA to 29-48 h (without DMSO). Intravenous injection of ALA led to a more homogeneous distribution of the ALA-derived porphyrins in the whole noduloulcerative BCC lesions.

Adult↗
PubMed2003

Effects of blood processing techniques on sodium and potassium values: a comparison between Aldabra tortoises (Geochelone gigantea) and Burmese mountain tortoises (Manouria emys).

BACKGROUND: Hematologic and plasma biochemical evaluations are routinely used in evaluating the chelonian patient, but appropriate processing techniques have been minimally defined. OBJECTIVES: This study was designed to compare the effects of temperature, time, anticoagulant, and species on sodium and potassium values in the Aldabra tortoise (Geochelone gigantea) and the Burmese mountain tortoise (Manouria emys). METHODS: Blood samples from 7 Aldabra tortoises and 8 Burmese mountain tortoises were collected into tubes without anticoagulant and tubes containing lithium heparin. Sodium and potassium concentrations were measured by flame photometry in serum and plasma harvested immediately after collection and from aliquots of whole blood stored at 4 degrees C and 25 degrees C for 5 to 120 minutes. RESULTS: In Aldabra tortoises, storage time and temperature had no significant effect on potassium concentrations in heparinized blood and in blood without anticoagulant. However, sodium concentrations in serum and plasma decreased significantly in samples without anticoagulant stored at 4 degrees C and 25 degrees C and in heparinized samples stored at 4 degrees C. In Burmese mountain tortoises, potassium concentrations in serum and plasma increased significantly with time in samples without anticoagulant and in heparinized samples stored at 4 degrees C and 25 degrees C, but the increases were less at 4 degrees C. Sodium concentrations in serum and plasma decreased significantly in blood without anticoagulant and heparinized blood stored at 4 degrees C and 25 degrees C. CONCLUSIONS: Storage of blood samples with and without anticoagulant at 4 degrees C significantly improved the stability of potassium and sodium concentrations in both species of tortoises. Early separation of red cells from serum or plasma after blood collection is especially important to ensure the reliability of potassium measurements.

Animals↗
PubMed1997

Acetylcholine-evoked potassium transport in the isolated guinea-pig pancreas.

In this study, K+ concentration was measured in effluent samples from superfused guinea-pig pancreatic pieces in control conditions and during stimulation with ACh, employing the technique of flame photometry. ACh (10(-7)-10(-5) M) evoked a dose-dependent and sustained increase in K+ concentration in the effluent (K+ release). The removal of Ca2+ from the superfusing medium and the addition of 10(-4) M EGTA caused a significant (P < 0.05) reduction in the ACh-evoked K+ efflux. Replacement of extracellular Cl- in the superfusing physiological salt solution with NO3- abolished the ACh-induced K+ efflux. In contrast, when Cl- was replaced with Br-, ACh still evoked marked K+ release. Pretreatment of pancreatic segments with the loop diuretic furosemide (10(-4) M) resulted in an inhibition of K+ efflux elicited by ACh. Stimulation of pancreatic segments with the Na(+)-K(+)-ATPase inhibitor ouabain (10(-3) M) caused a large efflux of K+. In the continuous presence of ouabain, ACh application elicited no further change in the K+ release. The results indicate that ACh-evoked K+ release from guinea-pig pancreatic segments is sensitive to ouabain, Cl-, furosemide and extracellular Ca2+ and that only the basal efflux is augmented by ouabain. The findings provide further evidence that a diuretic-sensitive coupled Na(+)-K(+)-Cl- cotransport system operates in the guinea-pig pancreas, as it does in other similar transporting epithelia, to bring about K+ mobilization.

Acetylcholine↗
PubMed1967

The distribution of [14C]sucrose within the skeletal muscle of the rat in vitro.

1. The distribution of [(14)C]sucrose within the plantaris muscle of the rat has been examined by suspending muscles in oxygenated Ringer containing this marker and subsequent analysis of the muscle.2. Histological examination of sections of muscle treated in this way indicates considerable distortion of muscle fibre pattern; this has been held to cast doubt upon the validity of such a method as a means of extracellular space examination.3. The rate of K(+) loss from muscles under these conditions has been examined by flame photometry. Up to 50% of the original muscle K(+) has been shown to be lost by efflux within approximately 1 hr from the commencement of soaking.4. It is considered that these findings indicate severe deterioration in the physiological condition of the muscle, and it is suggested that tissue hypoxia is chiefly responsible for this.

Animals↗
PubMed1983

A study of the mechanisms by which potassium moves through brain tissue in the rat.

The flux of K+ produced by electric current across the pia-arachnoid surface of the neocortex of anaesthetized rats has been studied with K+-selective electrodes in a cup at the surface and with flame photometry. The potential differences developed across three regions of the rat brain (neocortex, cerebellum, hippocampus) have been measured as [K+] was altered in fluid at the surface. The experimental results have been related to those that would be expected (i) if K+ moved principally by diffusion in extracellular space and (ii) if current flow through cells makes a significant contribution to K+ transfer. K movement produced by current across the neocortical surface accounted for 0.06 of the transfer of electric charge with small currents in either direction (ca. 5 microA mm-2) and with larger currents out of the tissue. Large currents (ca. 20 microA mm-2) into the tissue produced less K+ movement, but still more than the fraction 0.012 expected for purely extracellular flux. Alternating current pulses (5 Hz) with zero net transfer of charge produced no flux of K+ across the surface, while alternation with unequal durations produced the same effects as the equivalent steady charge transfer. The K+ flux lagged behind the onset and cessation of current with a time constant ca. 45 sec, approximately as expected from calculations with a model of the tissue. A surface-negative potential shift averaging 2 mV was observed when [K+ ]at the brain surface was increased from 3 to 12 mM. The time for development of half of the full potential change was 20 sec, with the solution changes complete in less than 4 sec. These results are inconsistent with the hypothesis that K+ movement through brain tissue occurs principally through intercellular clefts, except where these movements involve very localized gradients. They are consistent with the conclusion that ca. 5 times as much K+ flux passes through cells (probably largely glial cells) as through extracellular space, with fluxes driven by either extracellular voltage or concentration gradients.

Animals↗