[Lipoprotein (a)]

Lipoprotein (a) [Lp (a)] is a low density lipoprotein (LDL) disulfide-linked to apolipoprotein (a) [apo (a)] and considered to be an independent risk factor for atherosclerotic cardiovascular disease. Apo (a) has a high homology with plasminogen, which has stimulated a lot of interest in the mechanism of atherogenicity and thrombogenicity of this lipoprotein. Recent advances in this mechanism were reviewed. We are still unclear about the physiological role of Lp (a). This research aspect must receive attention in the future. Furthermore, the most pressing need is for drugs that will lower serum Lp (a) concentrations.

Increase of the delayed rectifier K+ and Na(+)-K+ pump currents by hypotonic solutions in guinea pig cardiac myocytes

To investigate the membrane current changes induced by membrane stretching, single guinea pig ventricular myocytes were superfused with solutions of various osmolarities, and the whole-cell current was recorded by the patch-clamp technique. The application of 70% and 130% osmolar bath solutions increased and decreased the amplitude of delayed rectifier K+ current (IK), respectively, whereas no obvious change was observed in the L-type Ca2+ current or the inward rectifier K+ current. When the Na(+)-K+ pump current (Ipump) was recorded by the use of high-Na+ (> 35 mmol/L) pipette solutions, Ipump was also increased and decreased by the superfusion of hypotonic and hypertonic solutions, respectively, in approximately half of the cells. An increase of the Ipump was also observed in the absence of external Na+, excluding a possibility that the enhancement of Ipump was secondary to an elevation of cytosolic Na+. In most cells that did not show the increase of Ipump, the hypotonic superfusion induced a gradual activation of Cl- current. The hypertonic superfusion did not cause any consistent change in the membrane Cl- conductance. Since the response of IK was observed in all experiments, its mechanism was studied. We failed to observe marked changes in the kinetic and conductance properties of IK in the hypotonic solution. The involvements of either the protein kinases or Ca2+ were also ruled out as major mechanisms underlying the IK response.

Etretinate administration reduces serum propeptide of type I procollagen level in patients with psoriasis

The serum carboxyterminal propeptide of type I procollagen (PICP) level in 26 patients with psoriasis was significantly lower than in control subjects (124 +/- 47 and 224 +/- 78 ng/ml, respectively; P < 0.001). The patients were divided into two groups, those treated with etretinate and untreated patients. PICP levels in the treated group were significantly lower than those in the untreated group (P < 0.001), but there was no difference between the control and untreated groups. In addition, there was a negative correlation between PICP levels and the serum etretinate concentration in treated patients (r = -0.622, P < 0.05). There was no difference between procollagen type III aminoterminal propeptide (PIIIP) levels in patients and controls, nor was there any significant difference between etretinate-treated and untreated patients. In cell culture studies, etretinate dose-dependently (from 10(-9) to 10(-5) M) decreased the PICP concentration in the medium of fibroblasts from both healthy subjects and patients. In osteoblast cell culture, PICP levels were reduced only in a high concentration of etretinate (10(-5) M). However, no change was observed in preadipose cells. Our in vivo and in vitro observations indicated that psoriasis per se did not affect either serum PICP or PIIIP levels, but that etretinate had an inhibitory effect on collagen synthesis by fibroblasts. Hence, the administration of etretinate to psoriatic patients is, at least in part, responsible for the reduction of serum PICP levels in these patients.

Voltage- and time-dependent block of I(f) by Sr2+ in rabbit sino-atrial node cells

The hyperpolarization-activated cation current (I(f)) was recorded in single myocytes dissociated from the rabbit sino-atrial node and the Sr(2+)-mediated block of I(f) examined. In the presence of 0.1-10 mM Sr2+, the activation phase of I(f) was followed by a slower decay during hyperpolarization. In the steady state I/V diagram, the Sr2+ block progressed with increasing hyperpolarization. Ba2+ also blocked I(f), but no time dependency could be observed. The blocking effect of Ca2+ was weak, and Mg2+ had little effect on I(f). The relationship between extracellular Sr2+ concentration [Sr2+]o and the block was described by a Hill coefficient of 1. The half-saturating [Sr2+]o were 2.0, 1.6, 1.1 and 0.65 mM at -90, -100, -110 and -120 mV, respectively. The rapid application of Sr2+ during the full activation of I(f) using the jet-stream method induced an exponential decline of I(f). The reciprocal time constants were linearly correlated to [Sr2+]o, suggesting 1:1 binding stoichiometry. The fractional electrical distance for the binding site was approximately 0.5 from the external side of the channel. Based on the multiple closed and open states for the I(f) channel, a mathematical model for the Sr2+ block was constructed in which the time course of I(f) in the presence of Sr2+ was described by the sum of three exponential functions. Fitting the model to the original traces revealed blocking and unblocking rates similar to those obtained from the jet-stream method. At -110 mV, the blocking rate was 410 M-1 s-1 while the unblocking rate was 0.16 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Cation-dependent gating of the hyperpolarization-activated cation current in the rabbit sino-atrial node cells

1. The gating properties of the hyperpolarization-activated cation current (I(f) or Ih) were investigated in single pacemaker cells dissociated from the rabbit sino-atrial node. 2. The whole-cell I(f) was recorded in the presence of different external cations. The inward I(f) was increased when external Na+ was replaced with K+, and was decreased in Li+ or Rb+ solution. In Tris+ and Cs+ solutions, the inward I(f) was negligible. The outward tail current recorded upon depolarization was largest in Li+ solution and smaller in a sequence of Na+, Tris+ and K+ solutions. In Rb+ and Cs+ solutions, only a small tail current was recorded. 3. The outward tail current had a 'shoulder' in Na+ solution, which was much delayed by replacing Na+ with Li+. In K+ solution, the decay of the tail current was much faster, and no obvious shoulder was recorded. The tail current was slowest in Li(+)-rich and 0 mM K+ solution, and was progressively accelerated by adding K+ over the range from 0 to 3 mM. The tail current at 30 mM [K+]o showed only a small shoulder. A common binding site to modulate the I(f) deactivation was suggested for monovalent cations. 4. The shoulder of the I(f) tail became more evident as I(f) was activated to a larger extent either by prolonging the duration or by increasing the amplitude of the preceding hyperpolarization in both Na+ and Li+ solutions. 5. The I(f) was first activated by hyperpolarizing the membrane to -110 mV, and then deactivated by depolarization. The inward tail current at -50 mV showed a single exponential decay. At more positive potentials, the shoulder of the outward tail currents became more evident and the rate of the final decay was increased. 6. The time course of I(f) activation was well fitted with the sum of two exponential functions. Time constants of both components were not affected by the external cation (Na+, K+ or Li+) replacement. Likewise, the quasi-steady state activation was conserved when external Na+ was replaced with Li+. 7. Two closed and three open states were assumed in a sequential state model of the I(f) channel. The cation effects were well simulated by assuming that the deactivation rate was selectively modulated. The flow of I(f) during the spontaneous action potential was calculated. The activation of I(f) started on repolarization to the maximum diastolic potential and reached a maximum in the middle of the diastolic period. Its peak amplitude was 14% of the net inward current during the diastolic period.

Serum lipid and apolipoprotein levels in patients with psoriasis

Although there have been extensive studies of serum lipid levels in psoriasis, the data are conflicting. In the present study, 38 male psoriatic patients and 40 age-matched male control subjects were studied. In addition, a 75 g oral glucose tolerance test (OGTT) was performed in 28 patients and 28 age-matched control subjects, in order to exclude subjects with abnormal OGTT values from the study. Twenty-two patients and 26 control subjects had normal OGTT values. There was a tendency for psoriatic patients with normal glucose tolerance to have increased triglyceride levels, but this was not statistically significant. Total cholesterol and high-density lipoprotein-cholesterol levels in patients were normal. However, serum apo B (P < 0.005), C-II (P < 0.005) and C-III (P < 0.005) levels in patients were significantly elevated compared with control subjects. When control subjects and patients with abnormal OGTT values were also included, a significant increase in triglyceride and apo E levels, and a significant decrease in the apo A-I level were observed in psoriatic patients. These findings suggest that psoriasis per se is associated with increases in apo B, C-II and C-III levels, but that this does not profoundly affect lipid levels. The abnormal lipoprotein metabolism may be related to the high incidence of atherosclerosis in psoriasis.

Background conductance attributable to spontaneous opening of muscarinic K+ channels in rabbit sino-atrial node cells

Single myocytes were dissociated from the rabbit sino-atrial node, and the membrane background conductance produced by spontaneous opening of the muscarinic K+ channels was investigated by recording whole-cell and single channel currents in both normal K+ (5.4 mM) and high-K+ (145 mM) external solutions. Increasing external K+ concentration ([K+]o) from 5.4 to 145 mM induced a large inward shift of the whole-cell current accompanied by considerable current fluctuations at -50 mV. The high-K(+)-induced current was both K+ selective and voltage dependent, which was examined by varying [K+]o. This current was almost completely suppressed by 1-5 mM Ba2+ or 2-10 mM Cs+ and it was partly blocked by 10 microM atropine. In high-K+ (145 mM) solution, 20 nM acetylcholine (ACh) further increased the K+ conductance as well as the current noise. The power density spectrum of the noise was fitted with a sum of two Lorentzian functions. The corner frequencies of both the slow (approximately 5 Hz) and fast (approximately 120 Hz) components were comparable between the noise before and during the ACh application. Internal dialysis with a non-hydrolysable derivative of ATP, 5'-adenylylimido-diphosphate (AMP-PNP) or Mg(2+)-free solution markedly decreased both the amplitude and fluctuations of the high-K(+)-induced current. The relation between the variance of the current fluctuations and the mean current amplitude was linear in every experiment using dialysis of AMP-PNP or Mg(2+)-free internal solution, or using superfusion of ACh. The slopes of these relations gave comparable single channel current amplitudes of -0.7 pA at -50 mV. These results indicate that the spontaneous opening of the muscarinic K+ channels is largely responsible for the high-K(+)-induced current. In the high-K+ solution, the variance-mean relation at -50 mV showed that the muscarinic K+ channel provides an inward current of 3.12 +/- 2.13 pA pF-1 (n = 23), which was about 60% of the total inward background current. In the normal K+ solution, the variance-mean relation at -50 mV indicated that an outward current of 6.0 +/- 2.0 pA (0.33 +/- 0.28 pA pF-1, n = 8) was provided by the K+ channel. The single channel current amplitude was estimated to be 0.06 +/- 0.02 pA (n = 9). Cell-attached recordings in the absence of ACh demonstrated sporadic and brief openings of channels identical to the ACh-induced channels. The power density spectra of the single channel currents exhibited kinetic properties comparable with those of the whole-cell currents.(ABSTRACT TRUNCATED AT 400 WORDS)

Fully mechanized latex immunoassay for serum lipoprotein(a)

We have developed a fully automated system to quantify lipoprotein(a) (Lp(a)) in human serum, based on the latex-enhanced turbidimetric immunoassay by application of the Immuno Chemistry Analyzer 501X. This assay was carried out with undiluted serum and was able to detect at Lp(a) levels higher than 4.0 mg/l. When judged to be out of range of the calibration (> 600 mg/l), the sample was automatically re-tested after automatic 10-fold dilution. Within-run C.V.s ranged from 1.9 to 2.1% and between-run C.V.s from 2.7 to 3.9%. Results by the present method were in good agreement with those by the in-house ELISA (r = 0.978) and the commercial ELISA (r = 0.990). The distribution of Lp(a) levels in sera from 508 healthy donors was highly skewed; the mean and median were 158 mg/l and 105 mg/l, respectively.

Lp(a): an acute-phase reactant?

The present study was designed to confirm the transient increases of plasma Lp(a) levels as an acute-phase reactant and to clarify the significance of these increases with the use of patients with acute myocardial infarction and patients subjected to surgical operations. Although interleukin 6, C-reactive protein and alpha 1 antitrypsin reached the maximal levels 1-2 days, 3 days and 4-5 days, respectively, after the episodes, the peak time of Lp(a) levels was delayed some extent in both patient groups. Studying the transient increases of Lp(a) levels as a function of apo(a) isoforms analyzed by density-gradient ultracentrifugation and SDS-PAGE, the higher-density Lp(a) particles preferentially containing high-molecular-weight apo(a) isoforms increased more than the lower-density Lp(a) particles containing low-molecular-weight apo(a) after the episodes. The immunohistochemical findings suggest that Lp(a) may play an important role as an acute-phase reactant in the repair of tissue injury, especially in the process of angiogenesis.

Turnover rate of the cardiac Na(+)-Ca2+ exchanger in guinea-pig ventricular myocytes

1. Single guinea-pig ventricular myocytes were voltage clamped using the whole-cell configuration of the patch-clamp technique and membrane current generated by the Na(+)-Ca2+ exchange mechanism recorded. 2. Rapid increases in cytosolic free calcium ([Ca2+]i) evoked by flash photolysis of either nitr-5 or DM-nitrophen resulted in current relaxations, arising from a redistribution of exchanger carrier conformations induced by the changes in [Ca2+]i. 3. Relaxation time constants were temperature dependent with a temperature coefficient over a 10 degrees C range (Q10) of approximately 3 and also voltage dependent, decreasing on hyperpolarization for membrane potentials in the range +40 to -80 mV. 4. The experimental results are consistent with consecutive exchange models having electrogenic Na+ translocation steps, together with a site density and turnover rate similar to that for the Na(+)-K+ pump.

[Analyses of ventricular arrhythmias in patients with progressive systemic scleroderma (PSS) by ambulatory electrocardiography]

Disorder of cardiac conduction and automaticity have been widely reported in patients with progressive systemic scleroderma (PSS). In the present study, ventricular arrhythmias were monitored by 24-hour ambulatory electrocardiographic recording (Holter monitor) in 30 female patients with PSS and 20 apparently healthy female controls. The following results were obtained: 1) In the waking state, 8 cases of 30 patients showed grade III, IVA or IVB of ventricular arrhythmias, according to Lown's classification. On the other hand, ventricular arrhythmias, such as grade III, IVA or IVB, were not observed in the control group. 2) In the patient group, grade IVA arrhythmias were observed during defecation, driving or light working, and grade IVB were during defecation, urination, light working or sleeping. These results suggest that it is important to examine arrhythmias by Holter monitors in patients with PSS.

Compensatory increase in intestinal apolipoprotein A-IV mRNA levels in the experimental nephrotic rat

Using experimental nephrotic rats, we investigated the potential feedback regulation of apolipoproteins (apos) at their hepatic and intestinal synthetic sites. Nephrotic syndrome (NS) was induced in rats by puromycin aminonucleoside (PAN) with a single intraperitoneal injection (120 mg/kg). In nephrotic rats, we observed a 60% reduction in serum apo A-IV levels despite a 3.4-fold increase in jejunum and a 1.5-fold increase in ileum apo A-IV mRNA levels, although hepatic apo A-IV levels were unchanged compared with those in pair-fed control rats. A strikingly positive correlation was observed between daily urinary excretion of apo A-IV and its mRNA levels in jejunum (r = .856, P < .01; n = 10) and ileum (r = .710, P < .05; n = 10). On the other hand, nephrotic rats had an 8.2-fold increase in serum apo A-I level associated with a 4.6-fold increase in hepatic and a small but significant increase in jejunum apo A-I mRNA levels. Compared with the fractional catabolic loss of albumin or apo A-IV, that of apo A-I was small and suggests a diminished level of glomerular filtration, leading to a further elevation in serum apo A-I level. Barring nonspecific effects of PAN, these data suggest that reduction of serum apo A-IV level due to urinary loss may directly upregulate mRNA levels in the small intestine. Alternatively, it may be the result of an effective filtration of a serum component unassociated with lipoproteins that normally and site-specifically reduces apo A-I and apo A-IV mRNA transcription.

Gating properties of ATP-sensitive K+ channels in the heart

Using a concentration jump technique (oil-gate method), the rate of closure or opening of the ATP-sensitive K+ channel was measured in response to varying the ATP concentration. The inside-out patch was prepared from dissociated ventricular cells of guinea-pig heart. The opening of the channel on jump to ATP-free solutions from various ATP concentrations showed a variable latent period before the almost exponential rise of the mean channel current. The mechanism of latency is not clear. On reapplying ATP, the channel closed without any obvious delay, and the time course was well fitted with a single exponential curve. The reciprocal time constant was proportional to the ATP concentration. The closing rate was explained by assuming a 1:1 binding stoichiometry and a rate constant of 51.7 or 5.6 mM-1s-1.

Suppressive effects of elimination diets on T cell responses to ovalbumin in hen's egg-sensitive atopic dermatitis patients

We investigated the effect of elimination diets on T cell responses to ovalbumin (OA) in hen's egg-sensitive atopic dermatitis (AD) patients. The proliferative responses of both peripheral blood mononuclear cells (PBMCs) and T cells with monocytes to OA decreased after elimination diets, but those to Candida albicans or phytohemagglutinin (PHA) did not decrease after elimination diets. The proliferative responses of CD4+ T cells with monocytes to OA decreased after elimination diets. In these patients, clinical symptoms of AD improved. These results indicate that T cells, especially CD4+ T cells, respond to food antigens in food-specific lymphocyte responses, and that elimination diets may be able to initiate reduction of the responsiveness of food-sensitive T cells, especially CD4+ T cells. Moreover, the surface marker phenotypes of the T cells responding to OA were analysed. Our results showed that CD4+CD45RA+ T cells tended to increase. The increase in circulating CD4+CD45RA+ T cells might function as systemic suppression against immune responses in the skin.

[Lp(a) lipoprotein in patients on maintenance hemodialysis--a study from apo(a) isoform]

It has been suggested that lipid abnormalities may be involved in the development of cardiovascular disorders in patients on maintenance hemodialysis (HD). Hypertriglyceridemia commonly accompanies this condition and is associated with decreased concentrations of HDL-cholesterol. Recent clinical interest has been paid to the disturbances of Lp(a) and apo (a) isoform in relation to cardiovascular disorders. Although high concentrations of Lp(a) are associated with ischemic heart disease, we are unaware of the availability of such data concerning patients on maintenance hemodialysis. We therefore compared levels of Lp(a) and the frequency of occurrence of their isoforms in 310 patients (chronic glomerulonephritis, N = 221; diabetic nephropathy, N = 77; polycystic kidney disease, N = 12) on maintenance hemodialysis and in 212 normal subjects. The following results were obtained. (1) HD patients showed significantly elevated levels of Lp(a) compared to normal subjects. (2) Studies of apo (a) isoform showed that HD patients showed high frequency of S2 and low frequency of S4. (3) HD patients, especially long-term patients, showed high frequency of double band (S2/S3). (4) There were no significant differences in the levels of Lp(a) and in the frequency of apo(a) isoform among 3 different etiological studies.

The ATP-sensitive K+ channel

A small conductance K+ channel, that is inactivated by ATP, was recently found in the inner membrane of rat liver mitochondria (Inoue et al., 1991). This finding clearly indicates that a variety of K+ channels, showing ATP-sensitivity, are widely distributed. ATP is an important compound in view of its participation in oxidative phosphorylation and as the source of high-energy phosphate for nearly every energy-requiring reaction in the cell. Therefore, it is easy to speculate that transducing the ATP concentration within a cell into an electrical signal is vital for most living cells. The opening of the ATP-sensitive K+ channel by a decrease in the ATP level shifts the membrane potential in a negative direction and in general depresses cell function. The closing of the channel by an increase in ATP depolarizes the membrane and enhances membrane excitability. It might be speculated that a sequence of amino acids common for the binding site of ATP is preserved and combined with different types of K+ channels, so that the gating with ATP is quite similar between different K+ channels, but the conductance properties are different. The large variability in the value of K1/2ATP in the same cells or between different tissues might be due to modulation of the reaction of ATP and the binding site. These ideas will be substantiated by clarifying the molecular structure of the ATP-sensitive K+ channel in the near future. The molecular mechanisms for the selective channel blockers, sulfonylureas, and for the K+ channel openers should also be clarified.

Quantification of exponential Na+ current activation in N-bromoacetamide-treated cardiac myocytes of guinea-pig

1. The activation kinetics of the Na+ current was investigated in single ventricular cells of the guinea-pig heart using an improved oil-gap voltage clamp method. The inactivation of the current was removed by an intracellular application of N-bromoacetamide (NBA) for less than 1 min. Although the NBA treatment slightly decreased the peak amplitudes (81.7 +/- 13.4% of control, n = 15), the Na+ current remained stable after the removal of inactivation. 2. On depolarization, the activation of Na+ current took an exponential time course after the capacitive current decreased to 5% of its peak amplitude (40-100 microseconds after the pulse onset). The time course of deactivation, recorded on repolarization from 1.2 ms depolarization, was also a single exponential. 3. The time constants of activation and deactivation were almost identical when compared at a given test potential within a range of -50 to -30 mV. These findings indicate that the cardiac Na+ current activation is determined by m1 kinetics, or one rate-limiting step. 4. At potentials negative to -60 mV, the deactivation was complete, and its time constant decreased e-fold per 20.3 +/- 1.8 mV hyperpolarization (n = 7). 5. The degree of steady-state activation (m(infinity)) was fitted to a Boltzmann equation with a slope factor of 7.4 +/- 0.3 mV and a half-maximum potential of -33.3 +/- 0.8 mV (n = 8). 6. Rate constants for the rate-limiting activation step between a closed state and an open state (alpha m, beta m), were determined from m(infinity) and tau m over a potential range between -100 and +50 mV. On a logarithmic scale, beta m-1 was a linear function of the membrane potential over the range -100 and -30 mV. 7. Fitting the newly determined activation kinetics to the rising phase of the action potential indicated that the activation kinetics in the present study is relevant to the physiological action potential. The density of the Na+ channels thus obtained was 1075 +/- 186 pF-1 (n = 6). 8. The measurements in the NBA-treated Na+ current were compared with those obtained without treatment.

Intercellular adhesion molecule-1 on cultured human melanoma cells: influence of cytokines

Adhesion molecules such as intercellular adhesion molecule-1 (ICAM-1) and its counter-receptor, lymphocyte function associated antigen-1 (LFA-1), play very important roles in immune responses. In this study, the effects of cytokines on cultured human melanoma cells (MMG2) were examined, especially focussing on the expression of ICAM-1 on MMG2 and lymphocyte adhesion to MMG2. Both the expression of ICAM-1 and HLA-DR on MMG2 increased after treatment with IFN-gamma. ICAM-1 expression began to increase earlier than HLA-DR expression. TNF-alpha and IL-1 beta also increased the expression of ICAM-1 on MMG2. However, these cytokines did not increase the expression of HLA-DR. IFN-gamma had a dose dependent effect on lymphocyte adhesion to MMG2. Pretreatment of IFN-gamma treated MMG2 with 84H10 (anti-ICAM-1 antibody) or pretreatment of lymphocytes with either SPV-L7 (anti-LFA-1 alpha antibody) or IOT10 (anti-LFA-1 beta antibody) inhibited the lymphocyte adhesion to MMG2. These results suggest that ICAM-1 molecules induced on melanoma cells by IFN-gamma can interact with LFA-1 molecules on lymphocytes.

Fast and slow blockades of the inward-rectifier K+ channel by external divalent cations in guinea-pig cardiac myocytes

The present patch-clamp study shows that external Mg2+, Ca2+ and Sr2+ decrease the unit amplitude of inward current through the inward-rectifier K+ channel in a concentration-dependent manner. Sr2+ produces a voltage-dependent flickering block as well, and the fractional electrical distance between the external orifice and the Sr2+ binding site (delta) is 0.73. The decrease of unit amplitude is reversible and voltage independent while it does not increase the noise level on the open-channel current. Unit current decreased by Mg2+ or Ca2+ has a longer mean open time, which is inversely proportional to the unit amplitude. External Mg2+ does not decrease the amplitude of unit outward current. A surface potential shift, measured using voltage-dependent Cs+ block (delta = 1.60), failed to explain the current decrease. Therefore, we conclude that (1) the external divalent cations cause an extremely fast channel block, which appears as a decreased amplitude of the unit current on the recording system; (2) the blocking site (fast site) is present near the external orifice of the channel, and it is separate from the blocking site (slow site) to which Cs+ and Sr2+ bind.