Clinical Factors Associated with High Glycemic Variability Defined by Coefficient of Variation in Patients with Type 2 Diabetes

Background

High glycemic Variability (HGV) has become a stronger predictor of hypoglycemia. However, clinical factors associate with HGV still are unknown.

Objective

To determine clinical variables that were associated with a coefficient of variation (CV) above 36% evaluated by continuous glucose monitoring (CGM) in a group of patients with diabetes mellitus.

Methods

A cohort of patients with type 2 diabetes (T2D) was evaluated. Demographic variables, HbA1c, glomerular filtration rate (GFR) and treatment regimen were assessed. A bivariate analysis was performed, to evaluate the association between the outcome variable (CV> 36%) and each of the independent variables. A multivariate model was constructed to evaluate associations after controlling for confounding variables.

Results

CGM data from 274 patients were analyzed. CV> 36% was present in 56 patients (20.4%). In the bivariate analysis, demographic and clinical variables were included, such as time since diagnosis, hypoglycemia history, A1c, GFR and treatment established. In the multivariate analysis, GFR <45 mL/min (OR 2.81; CI 1.27,6.23; p:0.01), A1c > 9% (OR 2.81; CI 1.05,7.51; p:0.04) and hypoglycemia history (OR 2.09; CI 1.02,4.32; p:0.04) were associated with HGV. Treatment with iDPP4 (OR 0.39; CI 0.19,0.82; p:0.01) and AGLP1 (OR 0.08; CI 0.01,0.68; p:0.02) was inversely associated with GV.

Conclusion

Clinical variables such as GFR <45 mL/min, HbA1C>9% and a history of hypoglycemia are associated with a high GV. Our data suggest that the use of technology and treatments able to reduce glycemic variability could be useful in this population to reduce the risk of hypoglycemia and to improve glycemic control.

Clinical Indicators of Fatal Dengue in Two Endemic Areas of Colombia: A Hospital-Based Case-Control Study

According to the World Health Organization, 98% of fatal dengue cases can be prevented; however, endemic countries such as Colombia have recorded higher case fatality rates during recent epidemics. We aimed to identify the predictors of mortality that allow risk stratification and timely intervention in patients with dengue. We conducted a hospital-based, case-control (1:2) study in two endemic areas of Colombia (2009-2015). Fatal cases were defined as having either 1) positive serological test (IgM or NS1), 2) positive virological test (RT-PCR or viral isolation), or 3) autopsy findings compatible with death from dengue. Controls (matched by state and year) were hospitalized nonfatal patients and had a positive serological or virological dengue test. Exposure data were extracted from medical records by trained staff. We used conditional logistic regression (adjusting for age, gender, disease's duration, and health-care provider) in the context of multiple imputation to estimate exposure to case-control associations. We evaluated 110 cases and 217 controls (mean age: 35.0 versus 18.9; disease's duration pre-admission: 4.9 versus 5.0 days). In multivariable analysis, retro-ocular pain (odds ratios [OR] = 0.23), nausea (OR = 0.29), and diarrhea (OR = 0.19) were less prevalent among fatal than nonfatal cases, whereas increased age (OR = 2.46 per 10 years), respiratory distress (OR = 16.3), impaired consciousness (OR = 15.9), jaundice (OR = 32.2), and increased heart rate (OR = 2.01 per 10 beats per minute) increased the likelihood of death (AUC: 0.97, 95% confidence interval: 0.96, 0.99). These results provide evidence that features of severe dengue are associated with higher mortality, which strengthens the recommendations related to triaging patients in dengue-endemic areas.

[Glycemic variability and oxidative stress in children, with type 1 diabetes attending a summer camp]

OBJECTIVE

To assess glycemic variability, oxidative stress and their relationship in children and adolescents with type 1 diabetes (T1DM) attending a summer camp.

PATIENTS AND METHOD

Cross-sectional study that included 54 children and adolescents with T1DM aged 7-16, attending a 7 day summer camp. Sociodemographic information, clinical data, and blood glucose values measured using an Accu-Chek Nano® glucose meter were recorded. Glucose variability markers (standard deviation [SD], low blood glucose index [LBGI], high blood glucose index [HBGI], mean amplitude of glycemic excursions [MAGE] and mean of daily differences [MODD]) were calculated. Oxidative stress was assessed by the measurement of 8-iso-prostaglandin F2 alpha (PGF2α) in a 24-hour urine sample collected at the end of the camp in 14 children.

RESULTS

The Median SD, MAGE and MODD indexes were in the high range (61, 131 and 58 mg/dl, respectively), LBGI in the moderate range (3.3), and HBGI in the low range (4.5). The mean HbA1c was 7.6% and the median urinary excretion rate of 8-iso-PGF2α was 864.39 pg/mg creatinine. The Spearman correlation coefficients between markers of glycemic variability (SD, HBGI, MAGE, MODD) were significant. Non-significant correlations were found between markers of glycemic variability and urinary 8-iso-PGF2α.

CONCLUSIONS

High glycemic variability was observed in children and adolescents attending a summer camp. However, no correlations were found between markers of glycemic variability and oxidative stress measured by urinary 8-iso-PGF2α. Further studies are needed to address the relationship between oxidative stress and glycemic variability in children with T1DM.

Exercise training and cytokines in breast cancer survivors

The purpose of this randomized controlled trial was to determine the effects of an 8-week (aerobic+strength) exercise training program (3 sessions/week) on the circulating cytokine levels of breast cancer survivors. We randomly allocated 16 female survivors of breast cancer (mean±SD age: 50±5 years) to an intervention or usual care (control) group (N=8 in each group). The intervention group followed an 8-week exercise program consisting of 3 sessions/week (session duration: 90 min). We measured the levels of the following cytokines before and after the intervention: beta-NGF, CTACK, eotaxin, FGF basic, G-CSF, gmCSFα, HGF, ICAM1, IFNα2, IFNγ, IL1α, IL1ß, IL1ra, IL2, IL2ra, IL3, IL4, IL6, IL7, IL8, IL9, IL10, IL12, IL13, IL15, IL16, IL17, IL18, IP10, LIF, MCS-F, MIP1α, MIP1β, MIF, MCP1, MCP3, MIG, PDGF bb, SCF, SCGFβ, SDF1α, TRAIL, TNFα, TNFβ, VCAM1, and VEGF. We only observed a significant interaction (group*time) effect for CTACK ( P=0.016), with mean values remaining stable in the intervention group but increasing over time in controls. The intervention program did not induce a significant decrease in the main breast cancer-related cytokines such as IL6 and IL8. A combined (aerobic+strength) 8-week exercise training intervention did not induce major changes in the basal cytokine levels of breast cancer survivors.

Voltage-gated Ca2+ currents in the human pathophysiologic heart: a review

The L-type Ca2+ current (I(Ca-L)) plays a key role in the cardiac excitation-contraction (E-C) coupling. Thus, it is a major target for many transmitters and hormones modulating cardiac function and, therefore, for pharmacological drugs to regulate inotropy. Ca2+ (and other) ion currents are commonly studied in animal tissues for practical reasons. Investigations in human cardiomyocytes started extensively only ten years ago with the development of patch-clamp techniques, enzymatic cell dissociation procedures, and surgical techniques. These studies have already provided valuable information concerning the nature, biophysics, pharmacology and regulation of human cardiac ionic currents in normal and diseased tissues. Interesting advances have been made to understand the role of I(Ca-L) in the development of chronic atrial fibrillation (AF). Alterations of single channel activity and regulation of macroscopic I(Ca-L) have also been found in heart failure (HF), ugh some of the data are divergent and puzzling. The T-type Ca2+ current (I(Ca-T)) has never been recorded in human cardiomyocytes. After a rapid overview of the basic properties of human cardiac Ca2+ currents, we focus on selected aspects of pathophysiology that are still unsolved.

Effects of aldosterone on transient outward K+ current density in rat ventricular myocytes

1. Aldosterone, a major ionic homeostasis regulator, might also regulate cardiac ion currents. Using the whole-cell patch-clamp technique, we investigated whether aldosterone affects the 4-aminopyridine-sensitive transient outward K+ current (I(to1)). 2. Exposure to 100 nM aldosterone for 48 h at 37 degrees C produced a 1.6-fold decrease in the I(to1) density compared to control myocytes incubated without aldosterone. Neither the time- nor voltage-dependent properties of the current were significantly altered after aldosterone treatment. RU28318 (1 microM), a specific mineralocorticoid receptor antagonist, prevented the aldosterone-induced decrease in I(to1) density. 3. When myocytes were incubated for 24 h with aldosterone, concentrations up to 1 microM did not change I(to1) density, whereas L-type Ca(2+) current (I(Ca,L)) density increased. After 48 h, aldosterone caused a further increase in I(Ca,L). The delay in the I(to1) response to aldosterone might indicate that it occurs secondary to an increase in I(Ca,L). 4. After 24 h of aldosterone pretreatment, further co-incubation for 24 h either with an I(Ca,L) antagonist (100 nM nifedipine) or with a permeant Ca(2+) chelator (10 microM BAPTA-AM) prevented a decrease in I(to1) density. 5. After 48 h of aldosterone treatment, we observed a 2.5-fold increase in the occurrence of spontaneous Ca(2+) sparks, which was blunted by co-treatment with nifedipine. 6. We conclude that aldosterone decreases I(to1) density. We suggest that this decrease is secondary to the modulation of intracellular Ca(2+) signalling, which probably arises from the aldosterone-induced increase in I(Ca,L). These results provide new insights into how cardiac ionic currents are modulated by hormones.

Heart failure after myocardial infarction: altered excitation-contraction coupling

BACKGROUND

Heart failure (HF) frequently follows the occurrence of myocardial infarction (MI). Questions about how HF develops and what cellular defects contribute to this dysfunction led to this study. Methods and Results-- MI was induced in rats by coronary artery ligation. Clinical examination of the post-MI (PMI) surviving animals indicated that they were in overt HF by all measures. Cellular examination of the cardiomyocytes by patch-clamp and confocal [Ca(2+)](i) imaging methods indicated that cellular function was significantly compromised. At the single-cell level, [Ca(2+)](i) transient amplitudes were reduced and contractions were decreased and slowed, although Ca(2+) current (I(Ca)) remained unchanged. The excitation-contraction coupling (ECC) gain function measured as Delta[Ca(2+)](i)/I(Ca) was significantly decreased. Ouabain, a cardiotonic steroid that blocks the Na(+),K(+)-ATPase and activates Ca(2+) entry via cardiac Na(+) channels, largely alleviated this defect.

CONCLUSIONS

After MI, I(Ca) becomes less able to trigger release of Ca(2+) from the sarcoplasmic reticulum. This failure of ECC is a major factor contributing to the development of contractile dysfunction and HF in PMI animals. The improved ECC gain, enhanced Ca(2+) entry, and augmented Ca(2+) signaling due to cardiotonic steroids contribute to the beneficial effects of these agents.

Microtubule disruption by colchicine reversibly enhances calcium signaling in intact rat cardiac myocytes

Using the whole-cell patch-clamp configuration in rat ventricular myocytes, we recently reported that microtubule disruption increases calcium current (I(Ca)) and [Ca(2+)](i) transient and accelerates their kinetics by adenylyl cyclase activation. In the present report, we further analyzed the effects of microtubule disruption by 1 micromol/L colchicine on Ca(2+) signaling in cardiac myocytes with intact sarcolemma. In quiescent intact cells, it is possible to investigate ryanodine receptor (RyR) activity by analyzing the characteristics of spontaneous Ca(2+) sparks. Colchicine treatment decreased Ca(2+) spark amplitude (F/F(0): 1.78+/-0.01, n=983, versus 1.64+/-0.01, n=1660, recorded in control versus colchicine-treated cells; P<0.0001) without modifying the sarcoplasmic reticulum Ca(2+) load and enhanced their time to peak (in ms: 6.85+/-0.09, n=1185, versus 7.33+/-0.13, n=1647; P<0.0001). Microtubule disruption also induced the appearance of Ca(2+) sparks in doublets. These alterations may reflect RyR phosphorylation. To further investigate Ca(2+) signaling in cardiac myocytes with intact sarcolemma, we analyzed [Ca(2+)](i) transient evoked by field stimulation. Cells were loaded with the fluorescence Ca(2+) indicator, Fluo-3 cell permeant, and stimulated at 1 HZ: [Ca(2+)](i) transient amplitude was greater and its decay was accelerated in colchicine-treated, field-stimulated myocytes. This effect is reversible. When colchicine-treated myocytes were placed in a colchicine-free solution for 30 minutes, tubulin was repolymerized into microtubules, as shown by immunofluorescence, and the increase in [Ca(2+)](i) transient was reversed. In summary, we demonstrate that microtubule disruption by colchicine reversibly modulates Ca(2+) signaling in cardiac cells with intact sarcolemma.

Microtubule disruption modulates Ca(2+) signaling in rat cardiac myocytes

Microtubules have been shown to alter contraction in cardiac myocytes through changes in cellular stiffness. However, an effect on excitation-contraction coupling has not been examined. Here we analyze the effects of microtubule disruption by 1 micromol/L colchicine on calcium currents (I(Ca)) and [Ca(2+)](i) transients in rat ventricular myocytes. I(Ca) was studied using the whole-cell patch-clamp technique. Colchicine treatment increased I(Ca) density (peak values, -4.6+/-0.4 and -9.1+/-1.3 pA/pF in 11 control and 12 colchicine-treated myocytes, respectively; P<0.05). I(Ca) inactivation was well fitted by a biexponential function. The slow component of inactivation was unchanged, whereas the fast component was accelerated after colchicine treatment (at -10 mV, 11.8+/-1.0 versus 6.7+/-1.0 ms in control versus colchicine-treated cells; P<0.005). [Ca(2+)](i) transients were analyzed by fluo-3 epifluorescence simultaneously with I(Ca). Peak [Ca(2+)](i) transients were significantly increased in cardiac myocytes treated with colchicine. The values of F/F(0) at 0 mV were 1.1+/-0.02 in 9 control cells and 1.4+/-0.1 in 11 colchicine-treated cells (P<0.05). beta-Adrenergic stimulation with 1 micromol/L isoproterenol increased both I(Ca) and [Ca(2+)](i) transient in control cells. However, no significant change was induced by isoproterenol on colchicine-treated cells. Colchicine and isoproterenol effects were similar and not additive. Inhibition of adenylyl cyclase by 200 micromol/L 2'-deoxyadenosine 3'-monophosphate blunted the colchicine effect. We suggest that beta-adrenergic stimulation and microtubule disruption share a common pathway to enhance I(Ca) and [Ca(2+)](i) transient.

Frequency-dependent increase in cardiac Ca2+ current is due to reduced Ca2+ release by the sarcoplasmic reticulum

"Ca(2+)-current facilitation" describes several features of increase in current amplitude often associated with a reduction in inactivation rate. The aim of this study was to investigate the mechanism of frequency-dependent increase in L-type Ca2+ current, I(Ca) taking advantage of recent knowledge on the control of Ca2+ current inactivation in cardiac cells. The frequency-dependent increase in I(Ca) was studied in adult rat ventricular myocytes using the whole-cell patch-clamp technique. I(Ca) was elicited by a train of 200-ms depolarizing pulses to +20 mV applied at various frequencies (0.2 up to 1.3 Hz). The increase in frequency induced a rate-dependent enhancement of I(Ca), or facilitation phenomena. In most cells, that showed two inactivation phases of I(Ca), facilitation was mainly related to slowing of the fast I(Ca) inactivation phase that occurred besides increase in peak I(Ca) amplitude. Both the decrease and slowing of the fast component of inactivation phase were attenuated on beta -adrenergic-stimulated current. Frequency-dependent I(Ca) facilitation paralleled a reduction in Ca2+ transient measured with fluo-3. After blocking sarcoplasmic reticulum-Ca2+ release by thapsigargin, the fast I(Ca) inactivation phase was reduced and facilitation was eliminated. Facilitation could not then be restored by 1 microM isoprenaline. Thus in rat ventricular myocytes, frequency-dependent facilitation of I(Ca)reflects a reduced Ca(2+)-dependent inactivation consecutive, in most part, to reduced Ca2+ load and Ca2+ release by the sarcoplasmic reticulum rather than being an intrinsic characteristic of the L-type Ca2+ channel.

Amount of calcium in the sarcoplasmic reticulum: influence on excitation-contraction coupling in heart muscle

Real-time imaging of the concentration of intracellular calcium ([Ca2+]i) has been carried out in heart cells using confocal imaging and patch-clamp techniques. Here we review recent investigations that used genetically engineered mice that lack phospholamban (PL knockout) to investigate the mechanisms of excitation-contraction (EC) coupling in heart. The heart cells from PL knockout (KO) mice exhibit [Ca2+]i transients that are larger than normal. Similarly, the elementary units of EC coupling, called Ca2+ sparks, were found to be more frequent in PL KO heart cells than normal heart cells. This finding is consistent with the findings that cell-wide [Ca2+]i transients arise as Ca2+ sparks sum during the EC coupling process. Finally, it was determined that the amount of Ca2+ within the sarcoplasmic reticulum (SR) was greater in the PL KO cardiac myocytes than in controls. Analysis of the results indicate that the larger [Ca2+]i transients and the more frequent Ca2+ sparks are due to the greater amount of Ca2+ within the SR of PL KO myocytes, as the Ca2+ current (ICa), which triggers the Ca2+ sparks and the [Ca2+]i transient, was the same in control and PL KO heart cells. We conclude that the amount of Ca2+ released from the SR per unit of triggering ICa increases as the SR Ca2+ content is augmented. Regulation of SR Ca2+ content is thus a means by which cardiac contractility is regulated.

Ca2+ flux through promiscuous cardiac Na+ channels: slip-mode conductance

The tetrodotoxin-sensitive sodium ion (Na+) channel is opened by cellular depolarization and favors the passage of Na+ over other ions. Activation of the beta-adrenergic receptor or protein kinase A in rat heart cells transformed this Na+ channel into one that is promiscuous with respect to ion selectivity, permitting calcium ions (Ca2+) to permeate as readily as Na+. Similarly, nanomolar concentrations of cardiotonic steroids such as ouabain and digoxin switched the ion selectivity of the Na+ channel to this state of promiscuous permeability called slip-mode conductance. Slip-mode conductance of the Na+ channel can contribute significantly to local and global cardiac Ca2+ signaling and may be a general signaling mechanism in excitable cells.

Defective excitation-contraction coupling in experimental cardiac hypertrophy and heart failure

Cardiac hypertrophy and heart failure caused by high blood pressure were studied in single myocytes taken from hypertensive rats (Dahl SS/Jr) and SH-HF rats in heart failure. Confocal microscopy and patch-clamp methods were used to examine excitation-contraction (EC) coupling, and the relation between the plasma membrane calcium current (ICa) and evoked calcium release from the sarcoplasmic reticulum (SR), which was visualized as "calcium sparks." The ability of ICa to trigger calcium release from the SR in both hypertrophied and failing hearts was reduced. Because ICa density and SR calcium-release channels were normal, the defect appears to reside in a change in the relation between SR calcium-release channels and sarcolemmal calcium channels. beta-Adrenergic stimulation largely overcame the defect in hypertrophic but not failing heart cells. Thus, the same defect in EC coupling that develops during hypertrophy may contribute to heart failure when compensatory mechanisms fail.

A chloride current component induced by hypertrophy in rat ventricular myocytes

The effect of hypertrophy on membrane currents of rat left ventricular myocytes was studied with the whole cell voltage-clamp method. We found that the slope of the total time-independent current density-voltage relationship was increased in hypertrophied cells. No change in the zero-current potential was observed. Surprisingly, the dominant time-independent current, the inward rectifier K+ current (measured as the Ba(2+)-sensitive current density) was unchanged. We therefore investigated the identity of the outwardly rectifying Ba(2+)-resistant current seen in the hypertrophied rat ventricular myocytes but not present in control cells. We found that this current 1) was not carried by monovalent cations, 2) was partially blocked by anthracene-9-carboxylic acid (9-AC), and 3) was sensitive to variations in extracellular Cl concentration. These findings are consistent with the current being carried at least partially by Cl-. The presence of an additional Cl(-)-dependent component in hypertrophied cells is supported by the actions of 9-AC on the measured action potentials (APs). 9-AC had no effect on control cells APs but prolonged hypertrophied cell APs. We conclude that a Cl- current component develops in hypertrophied rat heart cells. This component appears to shorten the AP duration and might thus provide protection from cardiac arrhythmias.

Modulation of electrical heterogeneity by compensated hypertrophy in rat left ventricle

Modulation of the regional distribution of the action potential by left ventricular hypertrophy and the role of the L-type Ca2+ current (I(Ca)) and transient outward current (I(to)) in the action potential duration (APD) were investigated in normal and hypertrophied rat ventricular myocytes from the apex (A), septum (S) and left ventricular free wall (FW) by using whole cell current- and voltage-clamp techniques. Hypertrophy was induced by abdominal aortic constriction. In control cells, the APD measured at 20% repolarization (APD20) assumed the shortest values in the A and the longest in the S, whereas FW cells showed intermediate values. Hypertrophy significantly prolonged the APD20 and increased APD variability within the A and FW regions but did not modify the APD in S cells. Analysis of the APD, I(Ca), and I(to) at the instant of 20% repolarization in the same cell showed that in control cells the shortest APD20 was associated with a prominent I(to) in the A and FW, whereas the long APD20 was identified with a lower I(to) in S myocytes. Hypertrophy-induced prolongation ofAPD20 was associated with a reduction in the I(to) in the A and FW. Significant correlations could be established between the APD20 and the "net current," defined as the algebraic addition of I(to) and I(Ca) in the A and FW control groups but not in the control S or hypertrophied cells whatever their origin. Our results indicate that interregional APD heterogeneity is lost while intraregional APD variability is increased in the A and FW during the hypertrophic process. These effects are largely due to a change in the balance between the I(Ca) and I(to), which is a major contributing factor to the heterogeneity of the initial phase of repolarization in the normal rat ventricle.

Ca2+ diffusion and sarcoplasmic reticulum transport both contribute to [Ca2+]i decline during Ca2+ sparks in rat ventricular myocytes

1. We sought to evaluate the contribution of the sarcoplasmic reticulum (SR) Ca2+ pump (vs. diffusion) to the kinetics of [Ca24]i decline during Ca2+ sparks, which are due to spontaneous local SR Ca2+ release, in isolated rat ventricular myocytes measured using fluo-3 and laser scanning confocal microscopy. 2. Resting Ca2+ sparks were compared before (control) and after the SR Ca2(+)-ATPase was either completely blocked by 5 microM thapsigargin (TG) or stimulated by isoprenaline. Na(+)-Ca2+ exchange was blocked using Na(+)-free, Ca(2+)-free solution (0 Na+, O Ca2+) and conditions were arranged so that the SR Ca2+ content was the same under all conditions when Ca2+ sparks were measured. 3. The control Ca2+ spark amplitude (281 +/- 13 nM) was not changed by TG (270 +/- 21 nM) or isoprenaline (302 +/- 10 nM). However, the time constant of [Ca2+]i decline was significantly slower in the presence of TG (29.3 +/- 4.3 ms) compared with control (21.6 +/- 1.5 ms) and faster with isoprenaline (14.5 +/- 0.9 ms), but in all cases was much faster than the global [Ca2+]i decline during a control twitch (177 +/- 10 ms). 4. The spatial spread of Ca2+ during the Ca2+ spark was also influenced by the SR Ca2+ pump. The apparent 'space constant' of the Ca2+ sparks was longest when the SR Ca2+ pump was blocked, intermediate in control and shortest with isoprenaline. 5. We conclude that while Ca2+ diffusion from the source of Ca2+ release is the dominant process in local [Ca2+]i decline during the Ca2+ spark, Ca2+ transport by the SR contributes significantly to both the kinetics and spatial distribution of [Ca2+]i during the Ca2+ spark.

Excitation-contraction coupling in heart: new insights from Ca2+ sparks

Ca2+ sparks, the elementary units of sarcoplasmic reticulum (SR) Ca2+ release in cardiac, smooth and skeletal muscle are localized (2-4 microns ) increases in intracellular Ca2+ concentration, [Ca2+]i, that last briefly (30-100 ms). These Ca2+ sparks arise from the openings of a single SR Ca2+ release channel (ryanodine receptor, RyR) or a few RyRs acting in concert. In heart muscle, Ca2+ sparks can occur spontaneously in quiescent cells at a low rate (100 s-1 per cell). Identical Ca2+ sparks are also triggered by depolarization because the voltage-gated sarcolemmal L-type Ca2+ channels (dihydropyridine receptors, DHPRs) locally increase [Ca2+]i and thereby activate the RyRs by Ca(2+)-induced Ca2+ release (CICR). The exquisite responsiveness of this process, reflected by the ability of even a single DHPR to activate a Ca2+ spark, is perhaps due to the large local increase in [Ca2+]i in the vicinity of the RyR that is a consequence of the close apposition of the DHPRs and the RyRs. In this review we examine our current understanding of cardiac excitation-contraction (EC) coupling in light of recent studies on the elementary Ca2+ release events or Ca2+ sparks. In addition, we further characterized Ca2+ spark properties in rat and mouse heart cells. Specifically we have determined that: (i) Ca2+ sparks occur at the junctions between the transverse-tubules and the SR in both species; (ii) Ca2+ sparks are asymmetric, being 18% longer in the longitudinal direction than in the transverse direction; and (iii) Ca2+ sparks individually do not produce measurable sarcomere shortening (< 1%). These results are discussed with respect to local activation of the RyRs, the stability of CICR, Ca2+ diffusion, and the theory of EC coupling.

Relation between the sarcolemmal Ca2+ current and Ca2+ sparks and local control theories for cardiac excitation-contraction coupling

Ca2+ sparks, the elementary events underlying excitation-contraction (E-C) coupling, occur when sarcoplasmic reticulum (SR) Ca2+ release channels open. They are activated locally by Ca2+ influx through sarcolemmal (SL) Ca2+ channels. By measuring the probability of spark occurrence under conditions in which their probability of occurrence is low, we address two important questions raised by our recent work: (1) When a Ca2+ spark is triggered, how many SL Ca2+ channels (at a minimum) contribute to its activation? (2) What is the relation between the subcellular local [Ca2+], produced by the opening of SL Ca2+ channels and the consequent SR Ca2+ release? By comparing the voltage dependence of Ca2+ sparks in rat ventricular myocytes with the Ca2+ current, we show that the opening of a single SL Ca2+ channel can trigger a Ca2+ spark. Furthermore, we deduce that the probability of SR Ca2+ release depends of the square of the local [Ca2+]i produced by SL Ca2+ channel openings. These results are discussed with respect to the properties of Ca2+-induced Ca2+-release (CICR) and the local control theory of excitation-contraction coupling.

Inhibition of HIV replication by CD8+ T cells correlates with CD4 counts and clinical stage of disease

We sought to evaluate the relationship of CD8+ T cell-mediated inhibition of autologous HIV replication in vitro to disease stage in HIV+ individuals. Depletion of CD8+ T cells from peripheral blood lymphocytes of 16 HIV+ subjects increased the percentage of virus-producing cultures from 56% to 81%. CD4+ T cells were purified from 52 HIV+ individuals and cultured alone or in the presence of autologous CD8+ T cells. In 13 (25%) subjects HIV replication was only detected in the absence of CD8+ T cells (inhibition positive); in 26 (50%) viral replication occurred both in the absence and presence of CD8+ cells (inhibition negative). In the remaining 13 (25%) subjects, CD8+ T cell-mediated inhibitory activity could not be evaluated because stimulation of their purified CD4+ T cells did not result in p24 production. In some virus culture-negative individuals, the inability to demonstrate HIV replication was due to the presence of low numbers of CD8+ T cells that co-purified with CD4+ T cells. Detection of inhibitory CD8+ T cells was associated with significantly higher CD4 counts and better clinical status compared with inhibition-negative subjects. These results demonstrate that CD8+ T cell-mediated inhibition of HIV replication correlates with disease stage, and thus may play a role in preventing disease progression. CD8+ T cells did not inhibit autologous HIV replication across a semipermeable membrane. Further, the ability of CD8+ T cells to prevent HIV replication did not correlate with lysis of autologous CD4+ T cells. Thus, CD8+ T cells inhibited autologous HIV replication in vitro through a contact-mediated non-lytic mechanism.

[Hepatitis C in primary care: a study of carriers and their families]

OBJECTIVE

A clinical epidemiological study at a health centre of carriers of hepatitis C virus (HCV) antibodies. The prevalence of HCV antibodies in immediate family members.

DESIGN

Crossover and descriptive.

SETTING

Chopera I Primary Care team. PATIENTS AND FAMILY MEMBERS: 37 carriers of HCV antibodies in the Centre's records. 52 family members of 21 carriers.

MEASUREMENTS AND MAIN RESULTS

A form containing the clinical and epidemiological data of each carrier was filled out. The diagnosis of HCV infection was made at the Health Centre in 72.22% of cases. 80% evolved towards a chronic hepatitis. 56.75% had a history of parenteral transmission. 37.75% had no history of risk factors. The epidemiological data of the family members was recorded and transaminasaemia and the HCV antibodies were determined. Four cases (8.33%) with altered transaminase and three cases (6.82%) of positive antibodies were found.

CONCLUSIONS

Existence of a high percentage of Hepatitis C of no known origin and a greater prevalence of carriers among family contacts than in the population as a whole. Essential role of Primary Care in the detection and follow-up of HCV carriers. A need for definitive studies on sexual transmission and the possible existence of other transmission routes. The setting-up of preventive measures against these routes.