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At least 145 records · Page 8Linked to original sources
PubMed1996

Electrical conductivity of tear fluid in healthy persons and keratoconjunctivitis sicca patients measured by a flexible conductimetric sensor.

BACKGROUND: It is known that the osmolarity of tears increases in keratoconjunctivitis sicca (KCS) patients and therefore could be a sensitive and specific indicator for the diagnosis of KCS. However, owing to the difficulties in using the current methods of tear fluid measurement these procedures have not been employed in clinical practice. A newly devised flexible conductimetric sensor fabricated using microelectronic techniques is small and flexible enough to be placed on the ocular surface to measure the electrical conductivity can be considered as an indirect function of electrolyte activity, or osmolarity. Therefore, we applied this new sensor to measure the tear fluid conductivity in KCS patients and healthy volunteers. METHODS: A flexible conductimetric sensor, consisting of a hydrophilic polytetrafluoroethylene membrane placed between two gold-coated layers, was placed directly into the temporal conjunctival cul-de-sac. The tear fluid conductivity was monitored graphically on a computer display. The sodium chloride concentration of tear fluids was calculated from the calibration curve and converted to the equivalent electrolyte concentration. RESULTS: The electrolyte concentrations were 324.8 +/- 41.0 mEq/1 in KCS patients (29 samples obtained from 16 KCS patients) and 296.4 +/- 30.1 mEq/1 in healthy persons (33 samples obtained from 17 healthy persons). The difference was significant (P < 0.01). A positive correlation was found between the electrolyte concentrations in KCS and the rose bengal score (coefficient = 0.36). CONCLUSION: The tear fluid conductivity in healthy persons and KCS patients could be monitored without ocular damage, and the measured values were consistent with previous reports. This method will be a new diagnostic tool for detecting tear abnormalities.

Adult↗
PubMed1994

Dielectric properties of human blood and erythrocytes at radio frequencies (0.2-10 MHz); dependence on cell volume fraction and medium composition.

The dielectric properties of human erythrocytes (red blood cells) suspended in whole blood and in isotonic media at various volume fractions (haematocrits) have been studied in the frequency range 0.2-10 MHz, in which the so-called beta-dispersion due to the Maxwell-Wagner effect is known to occur. The capacitance and conductance at 25 degrees C were measured by an instrument interfaced to a computer. The rectangular sample cavity (1 ml volume) contained four pure gold electrode pins, and the sample could be circulated by a roller pump. The frequency-dependence of the permittivity and conductivity were fitted by non-linear least squares regression. Corrections were applied for non-linearity in the dielectric increment at high haematocrit, and for electrode polarisation when diluting the blood in saline. Data were interpreted in terms of a simple equivalent resistor-capacitor circuit. From the measured haematological values the specific membrane capacitance (Cm) and the conductivities internal and external to the cells (sigma i' and sigma o' respectively) were estimated. The conductivities behaved in a predictable manner with a mean of 0.458 S.m-1 (s.d. +/- 0.044) for sigma i', whereas the value of Cm (and indeed the actual capacitance of the suspension) was dependent on the amount of plasma present. Hence, in stationary normal (anticoagulated) whole blood samples, Cm was as high as 2.98 mu F.cm-2 (s.d. +/- 0.40), in contrast to about 0.9 mu F.cm-2 in blood diluted more than two-fold (to less than 20% hct) in isotonic media. The high value remained when the diluent was plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Cells↗
PubMed1984

Effects of antidiuretic hormone on cellular conductive pathways in mouse medullary thick ascending limbs of Henle: I. ADH increases transcellular conductance pathways.

This paper reports experiments designed to assess the relations between net salt absorption and transcellular routes for ion conductance in single mouse medullary thick ascending limbs of Henle microperfused in vitro. The experimental data indicate that ADH significantly increased the transepithelial electrical conductance, and that this conductance increase could be rationalized in terms of transcellular conductance changes. A minimal estimate (Gminc) of the transcellular conductance, estimated from Ba++ blockade of apical membrane K+ channels, indicated that Gminc was approximately 30-40% of the measured transepithelial conductance. In apical membranes, K+ was the major conductive species; and ADH increased the magnitude of a Ba++-sensitive K+ conductance under conditions where net Cl- absorption was nearly abolished. In basolateral membranes, ADH increased the magnitude of a Cl- conductance; this ADH-dependent increase in basal Cl- conductance depended on a simultaneous hormone-dependent increase in the rate of the net Cl- absorption. Cl- removal from luminal solutions had no detectable effect on Ge, and net Cl- absorption was reduced at luminal K+ concentrations less than 5mM; thus apical Cl- entry may have been a Na+, K+, 2Cl- cotransport process having a negligible conductance. The net rate of K+ secretion was approximately 10% of the net rate of Cl- absorption, while the chemical rate of net Cl- absorption was virtually equal to the equivalent short-circuit current. Thus net Cl- absorption was rheogenic; and approximately half of net Na+ absorption could be rationalized in terms of dissipative flux through the paracellular pathway. These findings, coupled with the observation that K+ was the principal conductive species in apical plasma membranes, support the view that the majority of K+ efflux from cell to lumen through the Ba++-sensitive apical K+ conductance pathway was recycled into cells by Na+, K+,2Cl- cotransport.

Animals↗
PubMed1984

Effects of antidiuretic hormone on cellular conductive pathways in mouse medullary thick ascending limbs of Henle: II. determinants of the ADH-mediated increases in transepithelial voltage and in net Cl-absorption.

Cellular impalements were used in combination with standard transepithelial electrical measurements to evaluate some of the determinants of the spontaneous lumen-positive voltage, Ve, which attends net Cl- absorption, JnetCl, and to assess how ADH might augment both JnetCl and Ve in the mouse medullary thick ascending limb of Henle microperfused in vitro. Substituting luminal 5 mM Ba++ for 5 mM K+ resulted in a tenfold increase in the apical-to-basal membrane resistance ratio, Ra/Rbl, and increasing luminal K+ from 5 to 50 mM in the presence of luminal 10(-4)M furosemide resulted in a 53-mV depolarization of apical membrane voltage, Va. Thus K+ accounted for at least 85% of apical membrane conductance. Either with or without ADH, 10(-4) M luminal furosemide reduced Ve and JnetCl to near zero values and hyperpolarized both Va and Vbl, the voltage across basolateral membranes; however, the depolarization of Vbl was greater in the presence than in the absence of hormone while the hormone had no significant effect on the depolarization of Va. Thus ADH-dependent increases in Ve were referable to greater depolarizations of Vbl in the presence of ADH than in the absence of ADH. 68% of the furosemide-induced hyperpolarization of Va was referable to a decrease in the K+ current across apical membranes, but, at a minimum, only 19% of the hyperpolarization of Vbl could be accounted for by a furosemide-induced reduction in basolateral membrane Cl- current. Thus an increase in intracellular Cl- activity may have contributed to the depolarization of Vbl during net Cl- absorption, and the intracellular Cl- activity was likely greater with ADH than without hormone. Since ADH increases apical K+ conductance and since the chemical driving force for electroneutral Na+, K+, 2Cl- cotransport from lumen to cell may have been less in the presence of ADH than in the absence of hormone, the cardinal effects of ADH may have been to increase the functional number of both Ba++-sensitive conductance K+ channels and electroneutral Na+, K+, 2Cl- cotransport units in apical plasma membranes.

Animals↗
PubMed1984

Single-length and double-length channels formed by nystatin in lipid bilayer membranes.

Nystatin forms two types of channels in sterol-containing planar bilayer membranes. One type is formed when it is added to only one side of the membrane; the other is formed when it is added to both sides of the membrane. The relative permeability of these channels to nonelectrolytes (urea and glycerol) is identical. The sensitivity of membranes to the one-sided action of nystatin is critically dependent on their thickness; in particular, membranes made from monoglycerides with more than 18 carbon atoms in their acyl chain are insensitive to nystatin's one-sided action. These data are consistent with a model in which the two types of channels formed by nystatin have essentially identical structures, except that the channel formed by its two-sided action is twice the length of that formed by its one-sided action, because it is a tail-to-tail dimer of the latter.

Amphotericin B↗
PubMed1991

Intracellular potassium activity and the role of potassium in transepithelial salt transport in the human reabsorptive sweat duct.

We have measured the intracellular potassium activity, [K+]i and the mechanisms of transcellular K+ transport in reabsorptive sweat duct (RSD) using intracellular ion-sensitive microelectrodes (ISMEs). The mean value of [K+]i in RSD is 79.8 +/- 4.1 mM (n = 39). Under conditions of microperfusion, the [K+]i is above equilibrium across both the basolateral membrane, BLM (5.5 times) and the apical membrane, APM (7.8 times). The Na+/K+ pump inhibitor ouabain reduced [K+]i is insensitive to the Na+/K+/2 Cl- cotransport inhibitor bumetanide in the bath. Cl- substitution in the lumen had no effect on [K+]i. In contrast, Cl- substitution in the bath (basolateral side) depolarized BLM from -26.0 +/- 2.6 mV to -4.7* +/- 2.4 mV (n = 3; *indicates significant difference) and decreased [K+]i from 76.0 +/- 15.2 mM to 57.7* +/- 12.7 mM (n = 3). Removal of K+ in the bath decreased [K+]i from 76.3 +/- 15.0 mM to 32.3 +/- 7.6 mM (n = 4) while depolarizing the BLM from -32.5 +/- 4.1 mV to -28.3* +/- 3.0 mV (n = 4). Raising the [K+] in the bath by 10-fold increased [K+]i from 81.7 +/- 9.0 mM to 95.0* +/- 13.5 mM and depolarized the BLM from -25.7 +/- 2.4 mV to -21.3* +/- 2.9 mV (n = 4). The K+ conductance inhibitor, Ba2+, in the bath also increased [K+]i from 85.8 +/- 6.7 mM to 107.0* +/- 11.5 mM (n = 4) and depolarized BLM from -25.8 +/- 2.2 mV to -17.0* +/- 3.1 mV (n = 4). Amiloride at 10(-6) M increased [K+]i from 77.5 +/- 18.8 mM to 98.8* +/- 21.6 mM (n = 4) and hyperpolarized both the BLM (from -27.5 +/- 1.4 mV to -46.0* +/- 3.5 mV, n = 4). However, amiloride at 10(-4) M decreased [K+]i from 64.5 +/- 0.9 mM to 36.0* +/- 9.9 mM and hyperpolarized both the BLM (from -24.7 +/- 1.4 mV to -43.5* +/- 4.2 mV) and APM (from -18.3 +/- 0.9 mV to -43.5* +/- 4.2 mV, n = 6). In contrast to the observations at the BLM, substitution of K+ or application of Ba2+ in the lumen had no effect on the [K+]i or the electrical properties of RSD, indicating the absence of a K+ conductance in the APM.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiloride↗
PubMed1991

Electrogenic bicarbonate secretion in the turtle bladder: apical membrane conductance characteristics.

We have recently shown that stimulation of electrogenic HCO3- secretion is accompanied by a simultaneous increase in short-circuit current (Isc, equivalent to HCO3- secretion rate under these conditions), apical membrane capacitance (Ca, proportional to membrane area), and apical membrane conductance (Ga, proportional to membrane ionic permeability). The current experiments were undertaken to explore the ionic basis for the increase in Ga and the possibility that the rate of electrogenic HCO3- secretion is regulated by changes in Ga. Membrane electrical parameters were measured using impedance-analysis techniques before and after stimulation of electrogenic HCO3- secretion with cAMP in three solutions which contained different chloride concentrations. In another series of experiments, the effects of an anion channel blocker, anthracene-9-carboxylic acid (9-AA), were measured after stimulation of electrogenic HCO3- secretion with cAMP. The major conclusions are: (i) a measurable apical Cl- conductance exists in control hemibladders; (ii) the transport-associated increase in Ga includes a Cl(-)-conductive component; (iii) Ga also appears to reflect a HCO3- conductance; (iv) the relative magnitudes of the apical membrane conductances to Cl- and HCO3- are similar; (v) 9-AA reduces Ga and Isc in cAMP-stimulated hemibladders; and (vi) alterations in Isc appear to be mediated by changes in Ga.

Animals↗
PubMed1984

Separation of ionic currents in the somatic membrane of frog sensory neurons.

Electrical properties of isolated frog primary afferent neurons were examined by suction pipette technique, which combines internal perfusion with current or voltage clamp using a switching circuit with a single electrode. When K+ in the external and internal solutions was totally replaced with Cs+, extremely prolonged Ca spikes, lasting for 5 to 10 sec, and Na spikes, having a short plateau phase of 10 to 15 msec, were observed in Na+-free and Ca2+-free solutions, respectively. Under voltage clamp, Ca2+ current (ICa) appeared at around -30 mV and maximum peak current was elicited at about 0 mV. With increasing test pulses to the positive side, ICa became smaller and flattened but did not reverse. Increases of [Ca]o induced a hyperbolic increase of ICa and also shifted its I-V curve along the voltage axis to the more positive direction. Internal perfusion of F- blocked ICa time-dependently. The Ca channel was permeable to foreign divalent cations in the sequence of ICa greater than IBa greater than ISr much greater than IMn greater than IZn. Organic Ca-blockers equally depressed the divalent cation currents dose- and time-dependently without shifting the I-V relationships, while inorganic blockers suppressed these currents dose-dependently and the inhibition appeared much stronger in the order of IBa = ISr greater than ICa greater than IMn = IZn.

Action Potentials↗
PubMedDate not supplied

The influence of arterial pressure changes on blood volume replacement after acute hemorrhage in the alert rat.

The fluid content of circulating blood was followed continuously by conductometric measurement of large vein hematocrit in the alert rat. Arterial pressure was registered simultaneously. 2.5-23% of the determined blood volume was withdrawn rapidly and the changes of fluid content (delta v) calculated. Determinations of plasma protein showed that calculated delta v(delta vapp) may exceed true delta v due to transvascular fluid inflow by maximally 38%. A very fast phase of fluid inflow into the circulation (delta vfapp, within 1 min) was observed at the beginning, followed by a slow phase (delta vsapp), the magnitude of both being proportional to the concomitant arterial pressure drop (delta p). At delta p = 0, delta vfapp was 20% of the volume of blood withdrawn, total replacement (delta vfapp + delta vsapp = volume withdrawn) being complete in 60 min. At delta p = -20 mm Hg the figures were 40% and 20 min, respectively. Experiments on splenectomized animals showed essentially the same relations, excepting that delta vsapp may have been underestimated in normal rats. An arterial pressure rise after hemorrhage may attenuate complete replacement. The results are discussed in terms of capillary fluid conductivity. Thus CFC may be in the order of 0.029 ml/min x mm Hg x 100 g.

Acute Disease↗
PubMed1975

Evidence for Ca-2+ control of the transducer mechanism in crayfish stretch receptor.

Recording from the dendrite membrane indicated a resting potential of minus-51.6 mV, which was reduced by inhibition of the Na+/K+ pump. Voltage clamp at rest revealed a small inward current between minus-50 and minus-80 mV and a larger outward current at clamp potentials of minus-40 to +30 mV. Using ramp-changes of muscle tension as stimuli a time-variant tension-induced inward current (TIC) became apparent, the amplitude of which decreased towards larger depolarizing voltages until at +18 mV the current reversed the direction. The time course of the conductance changes corresponds to similar phases in the generator potential. The outward current only responded to fast reductions in tension, decreasing transiently. A contribution of the active Na+/K+ pump to the hyperpolarizing potential response is suggested by the effects of K-removal or Na-substitution by Li+. In Na-free choline chloride media the generator potential and the TIC was depressed by 70-85%. Additional removal of Ca-2+ abolished the TIC. In contrast, lowering the Ca-2+ level in presence of Na+ decreased the membrane resistance and markedly enhanced the TIC (maximally eightfold at 10-minus 5M Ca-2+) while 75-150 mM Ca-2+ or intracellular application of a Ca-ionophore had the reverse effect.

Animals↗
PubMed1975

Evaluation of a conductometric method to determine the volume fraction of the suspensions of biomembrane-bounded particles.

Supported by the fact of correspondence between the results of several independent techniques compared, we recommend here a conductometric method as a simple, nondestructive and reliable tool for determining the volume fraction of the suspensions of membrane-limited particles of biological relevance. It requires only conductivity measurements on a suspension and its medium.

Animals↗
PubMed1983

Conductometric determination of methenamine.

A method of conductometric titration for determination of methenamine is presented. An aqueous solution of silicotungstic acid is used as titrant. The acid and methenamine form an insoluble compound in which the molar ratio of the acid to methenamine is 1:4. Conductometric curves were obtained, the shapes of which are suitable for accurate and reproducible determination of the end point of titration. The results show reasonable accuracy. Good reproducibility was achieved even when small quantities of methenamine had to be determined.

Chemical Phenomena↗