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Biomedical subjects

A Noma

Publications and source records attributed to A Noma.

At least 163 records · Page 9Linked to original sources
PubMed1988

Changes of serum apolipoprotein levels after oral administration of fat in human subjects.

Changes of serum apolipoprotein levels were studied every hour for 6 h after the administration of 55 g butter to 8 healthy male subjects. The mean serum apo A-IV level was significantly increased at 4 h (P less than 0.05) after fat ingestion compared to the mean initial level, although no significant changes of levels in other apolipoproteins (apo A-I, A-II, B, C-II, C-III, and E) were observed. The mean apo A-IV level in the triglyceride-rich lipoprotein (TRL) fraction (d less than 1.006) increased progressively over 6 h. In all 8 subjects, the time of peak concentration of apo A-IV in TRL fraction was delayed by 1-2 h compared to that in whole serum. On the other hand, the mean apo B-48 level in the fraction reached a peak at 4 h. These results raise the possibilities that some apo A-IV, newly synthesized or already existing in intestinal cells, may be directly secreted into the venous circulation and that apo A-IV and apo B-48 may distribute differently in different sizes of chylomicron. Alternatively, the amount of each apolipoprotein synthesized may depend upon the content of ingested fat. It is suggested that apo A-IV production by intestinal cells does not appear to be regulated by the rate of fat transport, and that apo A-IV does not play an important role in chylomicron formation compared to apo B-48.

Administration, Oral↗
PubMed1988

Further studies on the resolution of human mercapt- and nonmercaptalbumin and on human serum albumin in the elderly by high-performance liquid chromatography.

High-performance liquid chromatographic (HPLC) analysis of human serum albumin (HSA) on Asahipak GS-520 showed at least two peaks, the principal component corresponding to human mercaptalbumin (HMA) and the secondary one to nonmercaptalbumin (HNA). HPLC analysis of HSA on Asahipak ES-520 N showed three peaks, the principal component corresponding to HMA, the secondary one to HNA having mixed disulfide with cysteine or glutathione and the tertiary one to HNA oxidized higher than mixed disulfide. Two kinds of rapid HPLC for the resolution of HSA into HMA and HNA were developed by the present authors. Using these HPLC, the present authors found a significant decrease in the fraction of HMA in the elderly.

Aged↗
PubMed1988

Calcium-activated non-selective cation channel in ventricular cells isolated from adult guinea-pig hearts.

1. A class of Ca2+-activated non-selective cation channel was identified in ventricular cells, which were dissociated from adult guinea-pig hearts using collagenase. 2. Under cell-attached conditions the patch electrode filled with a Na+-rich solution recorded no obvious single-channel current at the resting membrane potential. Subsequent superfusion of the ventricular cell with a Na+-free Tyrode solution induced an inward-going single-channel current as well as contracture of the cell. Kinetics of this channel were not affected by varying the membrane potential. 3. Single-channel currents showing a conductance similar to those observed in the cell-attached patches were recorded in isolated inside-out membrane patches when the inner side of the membrane was exposed to a free Ca2+ concentration ([Ca2+]i) higher than 0.3 microM. The slope conductance of the channel was 14.8 +/- 2.9 pS (mean +/- S.D., n = 17) at 20-25 degrees C. 4. The reversal potential examined in the inside-out patch was about 0 mV irrespective of the Na+-rich, K+-rich, Li+-rich or Cs+-rich solutions on either side of the membrane, thereby indicating that the channel was almost equally permeable to these cations. 5. The open probability of the channel was increased by raising [Ca2+]i with the maximum value of 0.93 +/- 0.17 (n = 4) at about 10 microM [Ca2+]i. The dose-response relation was fitted to the saturation kinetics with a Hill coefficient of 3.0 and a half-maximum concentration of 1.2 microM [Ca2+]i. 6. The gating kinetics were complex; both the open and closed time histograms showed at least two exponential components with time constants of 3.8 +/- 1.3 ms and 140 +/- 110 ms for open time and 1.8 +/- 1.1 ms and 14.9 +/- 5.3 ms for closed time (n = 4) at 10 microM [Ca2+]i. Reduction of [Ca2+]i resulted in both a decrease of the time constant of the slow component in the open time histogram and an increase of the two time constants of the closed time histogram. 7. Contribution of the channel to the whole-cell current was discussed based on an estimation of the channel density, presumably about 0.04 approximately 0.4/microns 2. Maximum activation of the channel would produce 7.2 approximately 72 nS of membrane conductance, which would explain the reported magnitude of the Ca2+-mediated background conductance of the single myocyte. The channel may also contribute, at least in part, to the transient inward current which develops in Ca2+-overloaded cardiac cells.

Action Potentials↗
PubMed1988

A new oil-gate concentration jump technique applied to inside-out patch-clamp recording.

A new method was developed to instantaneously replace the solution on the inner side of an inside-out membrane patch in order to measure time courses with which active substances acted on single ionic channels. Inside-out membrane patches were isolated from single ventricular cells of the guinea pig heart. The recording bath consisted of two chambers separated by a partition having a narrow slit. Mixing of two test solutions through this slit was prevented by filling it with paraffin oil. The pipette tip with a tightly sealed inside-out membrane patch was moved through the oil from one solution to the other so that the pipette tip was instantaneously exposed to a new solution. When the pipette tip was jumped between different K+ concentrations, the leak current through the membrane patch increased or decreased with a half time of 6.3 +/- 3.0 ms (n = 15). The amplitude of single K+ channel currents changed to a new steady level within approximately 20 ms. These time courses were well explained by diffusion of K+ in the dead space between the pipette tip opening and the membrane patch. An application of this method to the ATP-regulated K+ channel revealed a latent period of 1-2 s before the channel started its activity after the instantaneous removal of ATP, whereas no obvious latency was observed in the rapid suppression of the channel, which was completed in 100-300 ms after reapplying ATP.

Adenosine Triphosphate↗
PubMed1987

Separation and quantitation of plasma free fatty acids as phenacyl esters by HPLC.

We have developed a rapid method for the separation of plasma free fatty acids as their phenacyl esters by high-performance liquid chromatography (HPLC) using a reversed-phase (C18) column. The derivatives of series of both saturated and unsaturated fatty acids (C12:0-C22:6) are simultaneously separated within 45 min and detected with ultraviolet at 241 nm. The limit of detection of fatty acids was approximately 0.5 nmol in 20 microL injected volume of extracts, and the coefficient of variation of the present method did not exceed 3.0%. Comparison of the results of the present HPLC method with those of gas chromatography, gave very good correlations for all fatty acids in human plasma.

Chromatography, High Pressure Liquid↗
PubMed1987

A new oil-gap method for internal perfusion and voltage clamp of single cardiac cells.

(1.) We designed a new technique to achieve fast voltage clamp, combined with internal perfusion. The single guinea-pig cardiac cell, dissociated by collagenase treatment, was stretched across an oil-gap (30-40 micron wide) from a pool of Tyrode solution to a pool of internal solution. Part of the cell membrane was disrupted in the internal solution by crushing on the cell, a tapered tip of a glass capillary. Through the open end, the intracellular medium was equilibrated with test solutions and electrical current was injected for the voltage clamp of the membrane in the Tyrode pool. (2.) The capacitive transient on stepping the membrane potential decayed with a time constant of 10-60 microseconds, depending on the capacitive area (20-80 pF). The time course was a single exponential in 46% of the atrial cells and in 66% of the ventricular cells. In these tissues the series resistance, approximated by a ratio of the time constant and Cm, was 686 +/- 180 k omega (n = 37) in the ventricular cells or 812 +/- 143 k omega (n = 18) in the atrial cells. The stable seal resistance (Rseal) established in the oil-gap was around 33 M omega in the ventricular cells and 100 M omega in the atrial cells. (3.) A rapid increase in the inward current followed by a slow decay was observed on repolarization over the range negative to the potassium equilibrium potential. From the inward rectification of both peak and late currents and suppressive effects of Cs+ on the current, the current changes were attributed to activation and inactivation of the inward rectifier K channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Dependence of junctional conductance on proton, calcium and magnesium ions in cardiac paired cells of guinea-pig.

1. The dependence of gap junctional conductance on the intracellular concentrations of H+, Ca2+ and Mg2+ was studied in paired myocytes dissociated enzymatically from guinea-pig ventricle. To apply an internal solution buffered to specific H+, Ca2+ or Mg2+ concentration directly to one aspect of the gap junction, the non-junctional membrane of one of the pair was mechanically ruptured. The junctional conductance was measured by clamping the membrane potential of the other cell using a two-pipette voltage-clamp method. 2. The conductance of the non-junctional membrane was kept low in comparison with that of the junctional membrane (less than 1/50) by replacing both external and internal K+ with Cs+. 3. The current-voltage (I-V) relation of the junctional conductance was linear over the potential range examined (from -100 to +100 mV). No voltage or time dependence was detected. 4. The conductance of the gap junction between the paired cells ranged from 90 to 3900 nS with a peak distribution at 1000 nS. 5. The effect of H+ was examined over the pH range 7.4-5.4, while keeping the free-Ca2+ concentration at zero, or pCa 6.3 or 7.0 using 2-10 mM-EGTA. The junctional conductance was almost constant from pH 7.4 to 6.5 and decreased in a dose-dependent manner with further acidification. There was no difference in the pH-conductance relationships at various Ca2+ concentrations. The Hill coefficient was approximately 2.4 and the half-maximum concentration (pK'H) was 6.1. 6. The closing effect of Ca2+ on the gap junction channel was examined over the concentration range from pCa 7 to 5, while keeping the pH at 7.4, 7.0 or 6.5. At each pH, increasing Ca2+ decreased the junctional conductance with similar Hill coefficients of about 3.4. The pCa-conductance relationship shifted toward a higher Ca2+ concentration range as the pH was lowered (pK'Ca = 6.6, 6.4 and 5.6, at pH 7.4, 7.0 and 6.5, respectively). 7. Increasing Mg2+ also caused a fall in the junctional conductance over the pMg range 3.0-2.0 with a pK'Mg of 2.5 (3.2 mM), and a Hill coefficient of 3.0. 8. These results suggest that there are two respective binding sites for divalent cations and H+, and that the gap junctional conductance is regulated reversibly by the ligand-receptor reactions. Comparing the threshold concentrations of Ca2+ and H+ for electrical uncoupling, it was concluded that Ca2+ plays a more important role in regulating the gap junctional conductance of cardiac cells under physiological conditions.

Action Potentials↗
PubMed1987

Identification of sodium-calcium exchange current in single ventricular cells of guinea-pig.

1. The Na-Ca exchange current was investigated in single ventricular cells from guinea-pig hearts by combining the techniques of whole-cell voltage clamp and intracellular perfusion. 2. The membrane conductance was minimized by blocking Ca and K channels as well as the Na-K pump. Under these conditions, when Ca2+ was loaded internally by a pipette solution containing 430 nM-Ca2+, changing the Li+-rich external solution to a Na+-rich one induced a significant inward current. Applying external Na+ in the absence of internal Ca2+ did not appreciably change the current. 3. In contrast, perfusing 1 mM-external Ca2+ in the presence of internal Na+ which was loaded by a 20 mM-Na+ pipette solution, induced a marked outward current. Ca2+ superfusion in the absence of internal Na+ caused only a small current change. 4. The current-voltage relation of external-Ca2+- and external-Na+-induced current showed almost exponential voltage dependence as given by the equation i = a exp (rEF/RT), where a is a scaling factor that determines the magnitude of the current and r is a partition parameter used in the rate theory and represents the position of the energy barrier in the electrical field, which indicates the steepness of the voltage dependence of the current. E, F, R and T have their usual meanings. The value of a was 1-2 microA/microF and r about 0.35 for the Ca2+-induced outward current. At very positive or negative potentials, the current magnitude became smaller than expected from an exponential relation. 5. The current was blocked by heavy metal cations, such as La3+, Cd2+, Mn2+ and Ni2+ and partially blocked by amiloride and D600. 6. The temperature coefficient (Q10) value of the Ca2+-induced outward current was 3.6 +/- 0.4 (n = 4) at 0 mV and 4.0 +/- 0.9 at 50 mV in the range between 21 and 36 degrees C. 7. The outward current magnitude showed a sigmoidal dependence upon the external Ca2+ concentration with a half-maximum concentration, K1/2 of 1.38 mM and a Hill coefficient of 0.9 +/- 0.2 (n = 5). 8. Sr2+ could replace Ca2+ with K1/2 of 7 mM. Mg2+ and Ba2+, however, did not replace Ca2+. 9. The inward current component also showed a sigmoidal external Na+ dependence with K1/2 of 87.5 +/- 10.7 mM and a Hill coefficient of 2.9 +/- 0.4 (n = 6). 10. The reversal potential of the current was obtained near the values expected for 3 Na+:1 Ca2+ exchange.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Voltage-dependent magnesium block of adenosine-triphosphate-sensitive potassium channel in guinea-pig ventricular cells.

1. The adenosine-5'-triphosphate (ATP)-sensitive K+ channel of guinea-pig ventricular cells was examined in the presence and absence of internal Mg2+ or Na+ using an open cell-attached configuration of the patch-clamp technique. 2. Millimolar concentrations of internal Mg2+ ([Mg2+]i) produced marked fluctuations in the outward current, and the amplitude of the open-channel current was reduced with increasing [Mg2+]i. Millimolar Na+ applied internally also decreased the mean amplitude of the outward current, but the increase in current noise was not obvious. These effects became larger when the membrane potential was shifted to be more positive from the K+ equilibrium potential (EK). At potentials negative to EK the inward current was affected by neither internal Mg2+ nor Na+. 3. The external application of Na+, Mg2+ or Ca2+, however, failed to affect the single-channel current. 4. After removal of both internal Mg2+ and Na+, the mean open-channel current-voltage relationship became virtually linear. Referring to these unblocked values, relative amplitudes were determined at different levels of [Mg2+]i or [Na+]i. The dose-response relations gave a Hill coefficient of approximately 1 for Mg2+ block and approximately 2 for Na+ block. The half-maximum concentrations (Kh) for both Mg2+ and Na+ block were shifted to lower values with increasing positive potentials. 5. The power-density spectrum of the open-channel current noise induced by internal Mg2+ showed a Lorentzian function with a corner frequency above 1 kHz, suggesting that the current noise is due to rapid fluctuations of open-channel current between blocked and unblocked states. The corner frequencies gave Mg2+ block and unblock rate constants which were of the order of 10(7) M-1 s-1 and 10(4) s-1, respectively. 6. With increasing external K+ concentration ([K+]o) from 0 to 140 mM the current fluctuations became less prominent, and Kh for Mg2+ block was shifted to higher values. Raising [K+]o enhanced the unblock rate derived from the noise analysis while the block rate was not significantly altered. 7. The above findings could be explained by assuming a binding site for one Mg2+ or two Na+ located 30-35% of the electrical drop across the membrane from the inner mouth of the channel, thereby resulting in the ionic block of K+ passage. An apparent inward rectification observed in the single-channel current-voltage relation is attributable to the blockade of the channel by intracellular Mg2+ and/or Na+.

Action Potentials↗