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At least 955 records · Page 53Linked to original sources
PubMed1992

The sympathetic response to euglycaemic hyperinsulinaemia. Evidence from microelectrode nerve recordings in healthy subjects.

Sympathetic nervous system activation by insulin has been suggested as a mechanism explaining the association between insulin resistance and hypertension. We further examined the effect of insulin by direct microneurographic muscle and skin nerve sympathetic activity recordings during euglycaemic insulin clamps in healthy subjects. The mean plasma insulin level was elevated from 5.3 +/- 0.7 to 92.2 +/- 2.2 mU/l in seven subjects during a 90-min one-step clamp. In six other subjects plasma insulin was further raised from 85.7 +/- 4.0 mU/l to 747 +/- 53 mU/l between 45-90 min (two-step clamp). Four of the latter subjects received a sham clamp with NaCl infusions only on a second recording session. At the low dose of insulin muscle nerve sympathetic activity increased from a resting level of 22.7 +/- 5.0 bursts per min to 27.7 +/- 5.0 bursts per min at 15 min (p less than 0.05). The increases in muscle nerve sympathetic activity were significant (p less than 0.001; ANOVA) throughout insulin infusion, with a slight further increase (from 29.2 +/- 1.6 to 32.3 +/- 1.9 bursts per min) at the supraphysiological insulin concentration. During sham clamps muscle nerve sympathetic activity did not increase. Both insulin clamps induced minor, but significant, increases in forearm venous plasma noradrenaline concentrations. Skin nerve sympathetic activity (n = 3) did not change during insulin infusions. Heart rate increased slightly but significantly (p less than 0.005), during the insulin clamps. Blood pressure was not notably affected. In conclusion, hyperinsulinaemia was associated with increased vasoconstrictor nerve activity to skeletal muscle and with no change of sympathetic outflow to skin.

Adult↗
PubMed1991

Microelectrode study of voltage-dependent Ba2+ and Cs+ block of apical K+ channels in the skin of Rana temporaria.

The blockage of the apical K+ channels in frog species Rana temporaria by Ba2+ and Cs+ is strongly voltage-dependent. The interaction of both blockers with the K+ channels was studied by recording relations between the K+ currents (IK) and the transepithelial and intracellular potential. Mucosal Ba2+ and Cs+ depress IK, hyperpolarize the cell and induce pronounced nonlinearities in the current/voltage (I/V) relations. The nonlinearities are caused by the voltage-dependent interaction of Ba2+ and Cs+ with the binding site. Consequently, the apical membrane resistance not only depends on the blocker concentration but also on the apical membrane potential. Also the fractional resistance, fRa, and the voltage divider ratio, fVa, will change with blocker concentration and voltage. Owing to this non-ohmic behaviour, measurements of fVa in the presence of Ba2+ deviate markedly from the expected fRa values. The inhibitory effect of Ba2+ and Cs+ was analysed at different transepithelial and apical membrane voltages. The relation between the Michaelis-Menten constants and the voltage could be fitted with equations based on Eyring rate theory with the assumption of a single binding site. With this model we calculated the relative electrical position of the binding site for the blocker (delta), referred to the extracellular side of the channel. We obtained for Ba2+, delta = 0.34 +/- 0.05 and for Cs+, delta = 0.81 +/- 0.01. Comparison of the results from apical and transepithelial I/V relations demonstrates that the analysis of the transepithelial data provides overestimated values of the Hill coefficient and results in an underestimation of delta.

Animals↗
PubMed1982

Applicability of available ion-selective liquid-membrane microelectrodes to intracellular ion-activity measurements.

The equations that govern the behavior of ion-selective electrodes are evaluated for the composition ranges of Li+, Na+, K+, Mg2+, Ca2+, Cl-, and HCO-3 encountered in living cells. Various cause-effect relations are detailed, especially those pertaining to calibration procedures. The relation of the accuracy of measurement to the expected signal range, particularly in connection with the uncertainty of interpolation, is emphasized. Relevant numerical parameters are given for all ISE's discussed, the selectivity characteristics being those of the most advanced membrane systems. Figures are provided for the calibration curves in the vicinity of the typical cytosol composition.

Animals↗
PubMed1988

Intracellular pH regulation in papillary muscle cells from streptozotocin diabetic rats: an ion-sensitive microelectrode study.

Intracellular pH regulation was studied in papillary muscle from STZ-induced diabetic rat hearts. In control bicarbonate solution there was no difference between the steady-state pHi values recorded from diabetic or normal papillary muscle. The addition of insulin had no effect on the pHi of either group. The amplitude of NH4+-induced alkalinization and the time course of recovery from alkalinization were similar in both normal and diabetic muscles. In both preparations, the recovery from alkalinization was similarly delayed by the disulfonic stilbene DIDS. This suggests the participation of a Cl-/HCO3- exchange in the recovery from alkalosis in rat myocardial cells that is not changed by diabetes. On the other hand, the amplitude of the acidification induced by the withdrawal of NH4+ was markedly increased in diabetic papillary muscles as compared to normal muscles. Moreover, there was a marked slowing down of the recovery from acidosis in the diabetics. The amplitude of NH+4 withdrawal-induced acidification was increased equally by amiloride in both normal and diabetic muscles. These findings suggest that diabetes is associated with a change in the activity of the amiloride-sensitive Na+/H+ exchange.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1980

Efficacy of the two-microelectrode voltage clamp technique in crayfish muscle.

Crayfish muscle fibres of different dimensions were voltage clamped and white noise current was injected into the fibres at various distances from the voltage clamp current electrode. The clamp current was measured and power spectral densities were calculated. This method revealed the efficacy of the voltage clamp in these fibres. In large fibres (l = 1.8-2.0 mm; diameter = 100-180 micrometer) a space clamp was achieved only for a band width delta f = 40 Hz. At a distance of 100 micrometer from the clamp electrodes delta f was 250-500 Hz. In fibres of medium size (l = 1.0-1.3 mm; diameter = 60-120 micrometer) delta f was about 80 Hz and about 800 Hz at a distance of 100 micrometer. In experiments with very small muscle fibres (l = 400-600 micrometer; diameter = 30-50 micrometer) delta f was more than 500 Hz. The improvement of the space clamp for the smaller muscle fibres resulted mainly from the reduced total membrane capacity, cm, of these fibres. The limitations of the space clamp could be derived from the impedance properties of the fibres. The band width of the space clamp correlated with the band width for which the square of the absolute impedance, /Zp/2, of the muscle fibre could be described by a simple RC-model. This correlation was demonstrated in a model circuit. Power density spectra of membrane current fluctuations were measured also. To optimize the resolution of these measurements the contribution of instrumental noise was minimized. The effects of instrumental noise are discussed.

Animals↗
PubMed1984

A microelectrode for continuous recording of volume fluxes in isolated perfused tubule segments.

Manufacture, properties and use of a micro enzyme electrode for continuous monitoring of volume fluxes in the isolated tubule preparation is described. The specific electrode is a galactose-oxidase enzyme electrode, which can be used to detect changes in raffinose concentrations. The electrode's response to raffinose is almost linear over concentrations from 0-12 mmol/l. The electrode equally responds to galactose as to raffinose but is insensitive to other sugars, to pH changes (from 6.0-8.0), CO2 (from 1-10%) and electrolytes tested. Reducing O2 from 100 to 10% and to 1%, leads to a reduction of the reading by 10% and 30%, respectively. The reading is almost doubled when the temperature is increased from 20-40 degrees C. Furthermore, reducing agents such as uric acid and ascorbic acid interfere with the reading. If these substances and raffinose are omitted from the perfusate for isolated perfused proximal mouse tubules, the reading is identical in perfusate and collected fluid, indicating that the tubular epithelium does not produce substances in sufficient amounts to interfere with the electrode reading. After addition of 6 mmol/l raffinose to the perfusate the raffinose concentration in the collected fluid of 0.76 +/- 0.05 mm segments of straight proximal mouse tubules (perfusion rate = 3.4 +/- 0.45 nl/min) is 10.2 +/- 0.3 mmol/l, indicating a volume reabsorption of 1.5 +/- 0.3 nl/min. Peritubular application of acetazolamide reduces the volume reabsorption by 42 +/- 4%.

Animals↗
PubMed1984

A microelectrode for continuous monitoring of redox activity in isolated perfused tubule segments.

The design and application of a micro-plantinum electrode for continuous monitoring of reducing activity in the isolated tubule preparation is described. The electrodes response to H2O2 up to 0.1 mmol/l, to uric acid up to 0.3 mmol/l, ascorbic acid up to 1.0 mmol/l and cysteine up to 2.0 mmol/l is almost linear. The electrode is insensitive to extracellular ions, to changes of pH (5.5-8.0), CO2 (1-10%) and O2 (1-100%). The reading of the electrodes is almost doubled when the temperature is increased from 20-40 degrees C. When reducing substances are omitted from the perfusate for isolated perfused proximal tubules of the mouse, the reading is identical in perfusate and collected fluid, indicating that the tubular epithelium does not produce redox substances in sufficient amount to interfere with the electrode reading at flow rates approximately 10 nl/min. When the tubule is perfused with solutions containing 0.3 mmol/l uric acid, the uric acid concentration in the collected fluid is 0.16 +/- 0.01 mmol/l after a contact time of 1.36 +/- 0.1 S, revealing net uric acid reabsorption. Adding probenecid to the luminal perfusion fluid leads to a 37.5 +/- 1.0% increase of uric acid concentration in collected fluid, disclosing the inhibitory effect of probenecid on uric acid reabsorption. If 0.3 mmol/l uric acid is added to the bath, 0.017 +/- 0.002 mmol/l uric acid is detected in the luminal fluid. The entry of uric acid into the lumen is abolished by 10(-4) mol/l pyrazinamide.

Animals↗
PubMed1984

A microelectrode for continuous monitoring of glucose concentration in isolated perfused tubule segments.

The design and the application of a micro-enzyme-electrode for continuous monitoring of glucose concentration in the isolated tubule preparation is described. The principle of the electrode is the amperometric detection of hydrogen peroxide, which is a product of the oxidation of D-glucose by glucose oxidase immobilized at the tip of a micro-electrode. The resulting current causes a voltage deflection across a resistor in series with the electrode that is correlated directly with the glucose concentration. The electrode response to glucose is almost linear over the concentration range from 0 to 12 mmol/l with a slightly diminished slope in the higher range. Other sugars (12 mmol/l raffinose, galactose, fructose, sucrose, mannitol), pH (from 6.5 to 8.0) and pCO2 (from 1 to 10 kPa) do not influence the reading. A reduction of pO2 in the test solution to 1 kPa blunts the reading. Raising the temperature from 20 degrees C to 40 degrees C leads to a pronounced increase of the voltage deflection at a given glucose concentration. Interference is observed with strongly reducing agents such as L-cysteine, ascorbic acid and uric acid. At defined conditions the electrode is well suited to measure continuously glucose concentration in the luminal fluid at the collection site of the isolated perfused tubule of the kidney. Experiments are presented which illustrate the performance of the glucose electrode in this isolated tubule set-up. Peritubular reduction of potassium concentration or the application of ouabain diminish glucose reabsorption.

Animals↗
PubMed1976

Work-induced potassium changes in skeletal muscle and effluent venous blood assessed by liquid ion-exchanger microelectrodes.

Using liquid ion-exchanger semimicroelectrodes with a side pore, we measured changes of extracellular potassium concentration (Ke+) in adult rabbit and cat gastrocnemius muscles and in venous effluent blood flowing from the cat gastrocnemius muscle during various bouts of activity induced by sciatic nerve stimulation. 1. Isometric tetanic contractions (at 50 Hz) of various durations caused transient accumulation of Ke+ which was non-linearly related to the duration of muscle activity. The peak values of Ke+ in response to muscle stimulation were analogous in rabbits and cats, attaining values, e.g. after a 20-sisometric tetanus, between 8-9 mEq/1K+ in both species. 2. Potassium concentration in venous effleunt blood (K+ven) was transiently increased after isometric tetani. Since blood flow was measured at the same time, it was possible to calculate the amount of K+ lost by the muscle after tetani of various durations. A 32 g gastrocnemius muscle of the cat, for example, loses 9.36 +/- 1.52 muEqK+ after a 20-s isometric tetanus, which corresponds roughly to 0.5% of the total muscle potassium content. The loss of K+ in this muscle was 29.3 pEq K+ /impulse/100 g fresh muscle tissue. 3. There was no evident difference between the amount of K+ released during isometric tetani, or tetanic contractions performed under isotonic conditions. Single twitches evoked by indirect stimulation at 1 HZ for several minutes also induced a small rise in K+ven. 4. If the loss of K+ from the muscle into the blood stream is transiently prevented by arterio-venous occlusion installed immediately before a 10-s isometric tetanus, most K+ is released subsequently when blood flow is renewed, if the occlusion lasts for 20-25 s. It is not until blood flow is occuded for 40-60 s that most K+ is apparently resorbed and only a minor portion is released and is to be found in the venous blood. 5. The transient accumulation of muscle extra-cellular potassium may locally affect nerve endings, skeletal and smooth muscle cells.

Animals↗