Gambling helpline contacts during COVID-19-related availability restrictions: an interrupted time series analysis

OBJECTIVES

Gambling causes significant public health harms that are addressed in the help service network. Helplines are the most widely used service among those experiencing harms. The COVID-19 pandemic changed the global gambling landscape. This study assesses the effect of COVID-19-related restrictions on help-seeking for gambling via helplines.

STUDY DESIGN

We analysed data of national helplines in Sweden, Finland, and Denmark before and during the pandemic. The countries differed in their restrictions on the availability and accessibility of gambling during the pandemic.

METHODS

We performed an interrupted time series analysis of contact and web traffic data to helplines in Sweden, Finland, and Denmark before and during the COVID-19 pandemic (2017-2021). We also compared forecasted time series to the actual data to assess change.

RESULTS

The results show diverging patterns across the three countries. In Sweden, the number of helpline contacts remained stable throughout COVID-19, but there was an increasing trend in website visits. In Finland, the number of contacts declined during the first wave but rebounded during the second wave. Website visitation increased moderately. In Denmark, the number of contacts to the helpline soared over the COVID-19 period.

CONCLUSIONS

The diverging results suggest that help-seeking behaviour is likely to be impacted by differing policy approaches to gambling availability and limit-setting, visibility of helplines, and the prevalence of different forms of gambling in the three Nordic countries before and during the pandemic. This has implications for a preventive public health approach for gambling.

Incidence and treatment strategies of Penile Intraepithelial Neoplasia in Sweden 2000‐2019

Objectives

Materials and methods

Results

Conclusions

P2844Novel temperature guided irrigated ablation catheter: reproducibility of procedural efficiencies and acute success to isolate the pulmonary veins from two multicenter, feasibility studies

Background/Introduction

The novel catheter with 6 thermocouples for real-time temperature monitoring during irrigated radiofrequency ablation was designed to potentially enhance safety and effectiveness of the Smart Touch Surround Flow (STSF) catheter by incorporating real-time temperature sensing. A supplementary, novel algorithm was developed to modulate power to maintain target temperature during high power/short duration ablation (90W, 4s).

Purpose

This sub-analysis was performed to examine consistency and reproducibility of the procedural efficiencies and acute success of the novel catheter with optimized temperature control and microelectrodes in treating paroxysmal atrial fibrillation (PAF) across multiple sites from two initial feasibility studies, in standard (QMODE) and high power/short duration (QMODE+) temperature-control ablation modes.

Methods

The QDOT-MICRO (QMODE, NCT02944968; N=42) and QDOT-FAST (QMODE+, NCT03459196; N=52) studies were both prospective, non-randomized multi-center, clinical investigations completed across 6 and 7 centers, respectively, in Europe. Procedural efficiencies and acute success (PVI via entrance block) was examined across sites within the study.

Results

In the QDOT-MICRO study, median procedure time (105–155 min), RF ablation time (27.7–39.5 min), and fluoroscopy times (2.2–8 min) during QMODE ablation were similar across the 6 sites. In QMODE+ ablation, median procedure time, RF ablation time, and fluoroscopy times all fall within (84–134 min), (4.8–9.7 min) and (1.1–9.6 min), respectively, across the 7 sites. Fluid delivery by the study catheter was low in both studies: QDOT-MICRO 547±278mL (mean ± SD); QDOT-FAST 382±299. mL (mean ± SD); which is 39.1 and 57.4% lower, respectively, than reported in the SMART SF trial. Esophageal temperature probe was used in the majority of patients (30/42 for QDOT MICRO and 51/52 for QDOT-FAST). Acute PVI was successful in 100% of patients in both studies with no deaths or unanticipated AEs.

Conclusion(s)

In both feasibility studies, procedural efficiencies were reproducible across study sites in both QMODE and QMODE+, with 100% acute success and good safety outcomes. Efficiencies are likely to improve with further experience. These results need to be confirmed in larger trials.

Acknowledgement/Funding

Both Studies are Company Sponsored Studies funded by Biosense Webster, Inc.

Regulation of muscle glucose transport during exercise

In the present short review some factors affecting glucose utilization during exercise in skeletal muscle will be briefly described. Special focus will be put on the glucose transport step across the sarcolemma. Glucose transporters (GLUT4) are expressed at a surprisingly similar level in the different muscle fiber types in human skeletal muscle in contrast to findings in the rat. When working at the same absolute work load muscle glucose transport is decreased in trained compared with untrained muscle in part due to a decrease in GLUT4 translocation to the sarcolemma in trained muscle. However, when trained and untrained muscle are stressed severely by a workload taxing 100% of their peak oxygen uptake in a glycogen-depleted state, then glucose uptake is larger in trained than in untrained muscle and correlates with muscle GLUT4 content. Finally, the possible role of the AMP-activated protein kinase (AMPK) in regulating glucose uptake during exercise is discussed. It is indicated that at present no experiments definitively link activation of AMPK to activation of muscle glucose transport during exercise.

GLUT-4 translocation in skeletal muscle studied with a cell-free assay: involvement of phospholipase D

GLUT-4-containing membranes immunoprecipitated from insulin-stimulated rat skeletal muscle produce the phospholipase D (PLD) product phosphatidic acid. In vitro stimulation of PLD in crude membrane with ammonium sulfate (5 mM) resulted in transfer of GLUT-4 (3.0-fold vs. control) as well as transferrin receptor proteins from large to small membrane structures. The in vitro GLUT-4 transfer could be blocked by neomycin (a PLD inhibitor), and neomycin also reduced insulin-stimulated glucose transport in intact incubated soleus muscles. Furthermore, protein kinase B(beta) (PKB(beta)) was found to associate with the GLUT-4 protein and was transferred to small vesicles in response to ammonium sulfate in vitro. Finally, addition of cytosolic proteins, prepared from basal skeletal muscle, and GTP nucleotides to an enriched GLUT-4 membrane fraction resulted in in vitro transfer of GLUT-4 to small membranes (6.8-fold vs. unstimulated control). The cytosol and nucleotide-induced GLUT-4 transfer could be blocked by neomycin and N-ethylmaleimide. In conclusion, we have developed a cell-free assay that demonstrates in vitro GLUT-4 transfer. This transfer may suggest release of GLUT-4-containing vesicles from donor GLUT-4 membranes involving PLD activity and binding of PKB(beta) to GLUT-4.

Glycogen synthase localization and activity in rat skeletal muscle is strongly dependent on glycogen content

1. The influence of muscle glycogen content on glycogen synthase (GS) localization and GS activity was investigated in skeletal muscle from male Wistar rats. 2. Two groups of rats were obtained, preconditioned with a combination of exercise and diet to obtain either high (HG) or low (LG) muscle glycogen content. The cellular distribution of GS was studied using subcellular fractionation and confocal microscopy of immunostained single muscle fibres. Stimulation of GS activity in HG and LG muscle was obtained with insulin or contractions in the perfused rat hindlimb model. 3. We demonstrate that GS translocates from a glycogen-enriched membrane fraction to a cytoskeleton fraction when glycogen levels are decreased. Confocal microscopy supports the biochemical observations that the subcellular localization of GS is influenced by muscle glycogen content. GS was not found in the nucleus. 4. Investigation of the effect of glycogen content on GS activity in basal and insulin- and contraction-stimulated muscle shows that glycogen has a strong inhibitory effect on GS activity. Our data demonstrate that glycogen is a more potent regulator of glycogen synthase activity than insulin. Furthermore we show that the contraction-induced increase in GS activity is merely a result of a decrease in muscle glycogen content. 5. In conclusion, the present study shows that GS localization is influenced by muscle glycogen content and that not only basal but also insulin- and contraction-stimulated GS activity is strongly regulated by glycogen content in skeletal muscle.

Muscle glycogen content affects insulin-stimulated glucose transport and protein kinase B activity

We investigated the possible regulatory role of glycogen in insulin-stimulated glucose transport and insulin signaling in skeletal muscle. Rats were preconditioned to obtain low (LG), normal, or high (HG) muscle glycogen content, and perfused isolated hindlimbs were exposed to 0, 100, or 10,000 microU/ml insulin. In the fast-twitch white gastrocnemius, insulin-stimulated glucose transport was significantly higher in LG compared with HG. This difference was less pronounced in the mixed-fiber red gastrocnemius and was absent in the slow-twitch soleus. In the white gastrocnemius, insulin activation of insulin receptor tyrosine kinase and phosphoinositide 3-kinase was unaffected by glycogen levels, whereas protein kinase B activity was significantly higher in LG compared with HG. In additional incubation experiments on fast-twitch epitrochlearis muscles, insulin-stimulated cell surface GLUT-4 content was significantly higher in LG compared with HG. The data indicate that, in fast-twitch muscle, the effect of insulin on glucose transport and cell surface GLUT-4 content is modulated by glycogen content, which does not involve initial but possibly more downstream signaling events.

Glucose uptake is increased in trained vs. untrained muscle during heavy exercise

Endurance training increases muscle content of glucose transporter proteins (GLUT-4) but decreases glucose utilization during exercise at a given absolute submaximal intensity. We hypothesized that glucose uptake might be higher in trained vs. untrained muscle during heavy exercise in the glycogen-depleted state. Eight untrained subjects endurance trained one thigh for 3 wk using a knee-extensor ergometer. The subjects then performed two-legged glycogen-depleting exercise and consumed a carbohydrate-free meal thereafter to keep muscle glycogen concentration low. The next morning, subjects performed dynamic knee extensions with both thighs simultaneously at 60, 80, and until exhaustion at 100% of each thigh's peak workload. Glucose uptake was similar in both thighs during exercise at 60% of thigh peak workload. At the end of 80 and at 100% of peak workload, glucose uptake was on average 33 and 22% higher, respectively, in trained compared with untrained muscle (P < 0.05). Training increased the muscle content of GLUT-4 by 66% (P < 0. 05). At exhaustion, glucose extraction correlated significantly (r = 0.61) with total muscle GLUT-4 protein. Thus, when working at a high load with low glycogen concentrations, muscle glucose uptake is significantly higher in trained than in untrained muscle. This may be due to the higher GLUT-4 protein concentration in trained muscle.

Dissociation of AMP-activated protein kinase activation and glucose transport in contracting slow-twitch muscle

5'AMP-activated protein kinase (AMPK) has been suggested to be a key regulatory protein in exercise signaling of muscle glucose transport. To test this hypothesis, we investigated whether muscle glycogen levels affect AMPK activation and glucose transport stimulation similarly during contractions. Rats were preconditioned by a combination of swimming exercise and diet to obtain a glycogen-supercompensated group (high muscle glycogen content [HG]) with approximately 3-fold higher muscle glycogen levels than a glycogen-depleted group (low muscle glycogen content [LG]). In perfused fast-twitch muscles, contractions induced significant increases in AMPK activity and glucose transport and decreases in acetyl-CoA carboxylase (ACC) activity in both HG and LG groups. Contraction-induced glucose transport was nearly 2-fold (P < 0.05) and AMPK activation was 3-fold (P < 0.05) higher in the LG group compared with the HG group, whereas ACC deactivation was not different between groups. Thus, there was a significant positive correlation between AMPK activity and glucose transport in contracting fast-twitch muscles (r = 0.80, P < 0.01). However, in slow-twitch muscles with HG, glucose transport was increased 6-fold (P < 0.05) during contractions, whereas AMPK activity did not increase. In contracting slow-twitch muscles with LG, the increase in AMPK activity (315%) and the decrease in ACC activity (54 vs. 34% at 0.2 mmol/l citrate, LG vs. HG) was higher (P < 0.05) compared with HG muscles, whereas the increase in glucose transport was identical in HG and LG. In conclusion, in slow-twitch muscles, high glycogen levels inhibit contraction-induced AMPK activation without affecting glucose transport. This observation suggests that AMPK activation is not an essential signaling step in glucose transport stimulation in skeletal muscle.

Fiber type-specific expression of GLUT4 in human skeletal muscle: influence of exercise training

The fiber type-specific expression of skeletal muscle GLUT4 and the effect of 2 weeks of low-intensity training were investigated in 8 young untrained male subjects. Single muscle fibers were dissected from a vastus lateralis biopsy sample. Based on myosin heavy chain (MHC) expression, fibers were pooled into 3 groups (MHC I, MHC IIA, and MHC IIX), and the GLUT4 content of 15-40 pooled fibers was determined using SDS-PAGE and immunological detection. The GLUT4 content in pooled muscle fibers expressing MHC I was approximately 20% higher (P < 0.05) than that in muscle fibers expressing MHC IIA or MHC IIX. No difference in GLUT4 could be detected between fibers expressing MHC IIA or MHC IIX. Two weeks of exercise training increased (P < 0.05) the peak power output of the knee extensors by 13%, the maximal activities of citrate synthase and 3-hydroxyacyl-CoA dehydrogenase by 21 and 18%, respectively, and the GLUT4 protein content by 26% in a muscle homogenate. Furthermore, a 23% increase (P < 0.05) in GLUT4 was seen in fibers expressing the MHC I isoform after exercise training for 2 weeks. No change was seen in fibers expressing MHC IIA or MHC IIX. In conclusion, our data directly demonstrate that GLUT4 is expressed in a fiber type-specific manner in human skeletal muscle, although fiber type differences are relatively small. In addition, low-intensity exercise training recruiting primarily fibers expressing MHC I increased GLUT4 content in these fibers but not in fibers expressing MHC IIA or MHC IIX, indicating that GLUT4 protein content is related more to activity level of the fiber than to its fiber type, which is defined by expression of contractile protein.

Biochemical and functional characterization of the GLUT5 fructose transporter in rat skeletal muscle

Previous work has demonstrated that human skeletal muscle and adipose tissue both express the GLUT5 fructose transporter, but to date the issue of whether this protein is also expressed in skeletal muscle and adipose tissue of rodents has remained unresolved. In the present study we have used a combination of biochemical and molecular approaches to ascertain whether rat skeletal muscle expresses GLUT5 protein and, if so, whether it possesses the capacity to transport fructose. An isoform-specific antibody against rat GLUT5 reacted positively with crude membranes prepared from rat skeletal muscle. A single immunoreactive band of approx. 50 kDa was visualized on immunoblots which was lost when using anti-(rat GLUT5) serum that had been pre-adsorbed with the antigenic peptide. Subcellular fractionation of skeletal muscle localized this immunoreactivity to a single membrane fraction that was enriched with sarcolemma. Plasma membranes, but not low-density microsomes, from rat adipose tissue also displayed a single protein band of equivalent molecular mass to that seen in muscle. Reverse transcription-PCR analyses, using rat-specific GLUT5 primers, of muscle and jejunal RNA revealed a single PCR fragment of the expected size in jejunum and in four different skeletal muscle types. Sarcolemmal vesicles from rat muscle displayed fructose and glucose uptake. Vesicular uptake of glucose was inhibited by nearly 90% in the presence of cytochalasin B, whereas that of fructose was unaffected. To determine whether fructose could regulate GLUT5 expression in skeletal muscle, rats were maintained on a fructose-enriched diet for 4 days. This procedure increased jejunal and renal GLUT5 protein expression by approx. 4- and 2-fold respectively, but had no detectable effects on the abundance of GLUT5 protein in skeletal muscle or on fructose uptake in rat adipocytes. The present results show that GLUT5 is expressed in the sarcolemma of rat skeletal muscle and that it is likely to mediate fructose uptake in this tissue. Furthermore, unlike the situation in absorptive and re-absorptive epithelia, GLUT5 expression in insulin-sensitive tissues is not regulated by increased substrate supply.

Training effects on muscle glucose transport during exercise

Muscle glucose uptake is increased during exercise compared to rest. In general, muscle glucose uptake increases with increasing exercise intensity and duration. Whereas the arterio-venous concentration difference only increases 2-4-fold during exercise compared with rest the increase in muscle perfusion in 10-20 times and therefore quantitatively very important. During exercise the surface membrane glucose transport capacity increases in skeletal muscle primarily due to an increase in surface membrane GLUT4 protein content. Endurance training decreases muscle glucose uptake during exercise at a given absolute submaximal work-load despite a large increase in muscle GLUT4 protein content. We have shown that this decrease in glucose uptake at least in part is due to a blunted exercise-induced increase in sarcolemmal glucose transport capacity secondary to a blunted increase in sarcolemmal GLUT4 transporter number. Thus, endurance training leads to a marked reduction of the fraction of muscle GLUT4 that is translocated during a given submaximal exercise bout. Whether this is true also during exercise at higher intensities remains to be seen.

Molecular mechanisms involved in GLUT4 translocation in muscle during insulin and contraction stimulation

Studies in mammalian cells have established the existence of numerous intracellular signaling cascades that are critical intermediates in the regulation of various biological functions. Over the past few years considerable research has shown that many of these signaling proteins are expressed in skeletal muscle. However, the detailed mechanisms involved in the regulation of glucose transporter (GLUT4) translocation from intracellular compartments to the cell surface membrane in response to insulin and contractions in skeletal muscle are not well understood. In the present essay we report three different approaches to unravel the GLUT4 translocation mechanism: 1. specific pertubation of the insulin and/or contraction signaling pathways; 2. characterization of the protein composition of GLUT4-containing vesicles with the expectation that knowledge of the constituent proteins of the vesicles may help in understanding their trafficking; 3. degree of co-immunolocalization of the GLUT4 glucose transporters with other membrane marker proteins assessed by immunofluorescense and electron microscopy.

GLUT5 expression and fructose transport in human skeletal muscle

Biochemical and immunocytochemical studies have revealed that, in addition to GLUT1 and GLUT4, human skeletal muscle also expresses the GLUT5 hexose transporter. The subcellular distribution of GLUT5 is distinct from that of GLUT4, being localised exclusively in the sarcolemmal membrane. The substrate selectivity of GLUT5 is also considered to be different to that of GLUT1 and GLUT4 in that it operates primarily as a fructose transporter. Consistent with this suggestion studies in isolated human sarcolemmal vesicles have shown that fructose transport obeys saturable kinetics with a Vmax of 477 +/- 37 pmol.mg protein-1 min-1 and a Km of 8.3 +/- 1.2 mM. Unlike glucose uptake, fructose transport in sarcolemmal vesicles was not inhibited by cytochalasin B suggesting that glucose and fructose are unlikely to share a common route of entry into human muscle. Muscle exercise, which stimulates glucose uptake through the increased translocation of GLUT4 to the plasma membrane, does not increase fructose transport or sarcolemmal GLUT5 content. In contrast, muscle inactivity, induced as a result of limb immobilisation, caused a significant reduction in muscle GLUT4 expression with no detectable effects on GLUT5. The presence of a fructose transporter in human muscle is compatible with studies showing that this tissue can utilise fructose for both glycolysis and glycogenesis. However, the full extent to which provision of fructose via GLUT5 is important in meeting the energy requirements of human muscle during both physiological and pathophysiological circumstances remains an issue requiring further investigation.

Phosphatidylinositol 4-kinase, but not phosphatidylinositol 3-kinase, is present in GLUT4-containing vesicles isolated from rat skeletal muscle

Insulin stimulates the rate of glucose transport into muscle and adipose cells by translocation of glucose transporter (GLUT4)-containing vesicles from an intracellular storage pool to the surface membrane. This event is mediated through the insulin receptor substrates (IRSs), which in turn activate phosphatidylinositol (PI) 3-kinase isoforms. It has been suggested that insulin causes attachment of PI 3-kinases to the intracellular GLUT4-containing vesicles in rat adipose cells. Furthermore, it has also been shown that GLUT4-containing vesicles in adipose cells contain a PI 4-kinase. In the present study we investigate whether GLUT4-containing vesicles isolated from rat skeletal muscle display PI 3-kinase and/or PI 4-kinase activities. Insulin stimulation caused a rapid increase (5-15-fold increase compared with control) in the intracellular cytosolic IRS-1-associated PI-3 kinase activity. This PI 3-kinase activity was also present in a membrane preparation containing the insulin-regulatable pool of GLUT4 transporters. However, when GLUT4-containing vesicles were isolated by immunoprecipitation from basal and insulin-stimulated (3 min) skeletal muscle, the vesicles displayed PI 4-kinase, but not PI 3-kinase, activity. Insulin did not regulate the PI 4-kinase activity in the GLUT4-containing vesicles. In conclusion, GLUT4-containing vesicles from rat skeletal muscle contain a PI 4-kinase, but not a PI 3-kinase. It is suggested that, in skeletal muscle, insulin causes activation of the IRS/PI 3-kinase complex in an intracellular membrane compartment associated closely with the GLUT4-containing vesicles, but not in the GLUT4-containing vesicles themselves.

Palmitate transport and fatty acid transporters in red and white muscles

We performed studies 1) to investigate the kinetics of palmitate transport into giant sarcolemmal vesicles, 2) to determine whether the transport capacity is greater in red muscles than in white muscles, and 3) to determine whether putative long-chain fatty acid (LCFA) transporters are more abundant in red than in white muscles. For these studies we used giant sarcolemmal vesicles, which contained cytoplasmic fatty acid binding protein (FABPc), an intravesicular fatty acid sink. Intravesicular FABPc concentrations were sufficiently high so as not to limit the uptake of palmitate under conditions of maximal palmitate uptake (i.e., 4.5-fold excess in white and 31.3-fold excess in red muscle vesicles). All of the palmitate taken up was recovered as unesterified palmitate. Palmitate uptake was reduced by phloretin (-50%), sulfo-N-succinimidyl oleate (-43%), anti-plasma membrane-bound FABP (FABPpm, -30%), trypsin (-45%), and when incubation temperature was lowered to 0 degrees C (-70%). Palmitate uptake was also reduced by excess oleate (-65%), but not by excess octanoate or by glucose. Kinetic studies showed that maximal transport was 1.8-fold greater in red vesicles than in white vesicles. The Michaelis-Menten constant in both types of vesicles was approximately 6 nM. Fatty acid transport protein mRNA and fatty acid translocase (FAT) mRNA were about fivefold greater in red muscles than in white muscles. FAT/CD36 and FABPpm proteins in red vesicles or in homogenates were greater than in white vesicles or homogenates (P < 0.05). These studies provide the first evidence of a protein-mediated LCFA transport system in skeletal muscle. In this tissue, palmitate transport rates are greater in red than in white muscles because more LCFA transporters are available.

Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise

1. The effects of unaccustomed eccentric exercise on exercise metabolism during a subsequent bout of graded concentric exercise were investigated in seven healthy male subjects. Arterial and bilateral femoral venous catheters were inserted 2 days after eccentric exercise of one thigh (eccentric thigh) and blood samples were taken before and during graded two-legged concentric knee-extensor exercise. Muscle biopsies were obtained from the eccentric and control vastus lateralis before (rest) and after (post) the concentric exercise bout. 2. Maximal knee-extensor concentric exercise capacity was decreased by an average of 23 % (P < 0.05) in the eccentric compared with the control thigh. 3. The resting muscle glycogen content was lower in the eccentric thigh than in the control thigh (402 +/- 30 mmol (kg dry wt)-1 vs. 515 +/- 26 mmol (kg dry wt)-1, means +/- s.e.m., P < 0.05), and following the two-legged concentric exercise this difference substantially increased (190 +/- 46 mmol (kg dry wt)-1 vs. 379 +/- 58 mmol (kg dry wt)-1, P < 0.05) despite identical power and duration of exercise with the two thighs. 4. There was no measurable difference in glucose uptake between the eccentric and control thigh before or during the graded two-legged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, release of lactate decreased from this thigh (suggesting decreased glycogenolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the first, lighter part of the exercise (P < 0.05) suggested impaired triacylglycerol breakdown. 5. At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and concentric exercise increased sarcolemmal GLUT4 content and glucose transport capacity similarly in the two thighs. 6. It is concluded that in muscle exposed to prior eccentric contractions, exercise at a given power output requires a higher relative workload than in undamaged muscle. This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.

Sarcolemmal glucose transport and GLUT-4 translocation during exercise are diminished by endurance training

Glucose utilization during exercise of a given submaximal power output is decreased after endurance training. The aim of the present study was to elucidate the mechanisms behind this phenomenon by utilizing the sarcolemmal giant vesicle technique. Eight healthy young untrained men endurance trained one thigh for 3 wk. They then exercised both thighs simultaneously at the same work load (77% of peak O2 uptake of the untrained thigh) for 40 min. Training increased muscle GLUT-4 protein by 70% (P < 0.05). Glucose uptake during exercise was 38% lower (P < 0.05) in the trained (T) thigh than in the untrained (UT) thigh because of both a lower (P < 0.05) glucose extraction and blood flow in T. During exercise, sarcolemmal GLUT-4 protein content and glucose transport capacity increased significantly less in T than in UT muscle, and muscle glucose concentration was lower in T compared with UT (P < 0.05) at the end of exercise. It is concluded that, despite a large increase in muscle GLUT-4 with endurance training, exercise of a given submaximal power output increases muscle glucose uptake less in T than in UT muscle. It is suggested that the mechanism behind this phenomenon is blunted exercise-induced translocation of GLUT-4 to the sarcolemma, resulting in a blunted increase in sarcolemmal glucose transport in T muscle.

Fructose transport and GLUT-5 protein in human sarcolemmal vesicles

Sarcolemmal vesicles were produced from human skeletal muscle biopsy material obtained at rest and immediately after maximal dynamic exercise (100% maximal O2 uptake) for analysis of fructose transport and hexose transporter (GLUT-5) protein concentration. Human sarcolemmal vesicles displayed a time-dependent uptake of D-fructose that displayed saturable Michaelis-Menten type kinetics (maximal transport 477 +/- 37 pmol.min-1.mg protein-1; half-maximal concentration constant 8.3 +/- 1.2 mM). At a hexose concentration of 5 mM, vesicle transport rate was eight times faster for glucose than for fructose. Preincubation of human muscle vesicles with 35 microM cytochalasin B before the uptake assay resulted in > 95% inhibition in D-glucose uptake, whereas transport of D-fructose was unaffected. Sarcolemmal vesicles prepared from exercised human muscle showed a significant increase (49%) in vesicle GLUT-4 content (P < 0.03, n = 10), which accounts for the increase in vesicle glucose transport that we have recently reported [S. Kristiansen, M. Hargreaves, and E.A. Richter. Am. J. Physiol. 270 (Endocrinol. Metab. 33): E197-E201, 1996]. In contrast, exercise did not increase the vesicle GLUT-5 protein content or induce changes in vesicle fructose transport activity. In conclusion, we propose that fructose transport into human skeletal muscle occurs via a mechanism distinct from that utilized by glucose on the basis of differences in sensitivity to cytochalasin B and responsiveness to exercise. Furthermore, our findings signify that uptake of fructose in human skeletal muscle is mediated by the GLUT-5 transporter.

Eccentric contractions decrease glucose transporter transcription rate, mRNA, and protein in skeletal muscle

We have recently shown that eccentric contractions (ECs; forced lengthening of active muscle) elicit a delayed decrease in glucose transporter (GLUT-4) protein content in rat skeletal muscle and a decrease in subsequent contraction-stimulated glucose transport. Here, we investigate whether this decrease in total GLUT-4 protein after prior ECs is due to changes in GLUT-4 gene transcription rate and GLUT-4 mRNA level. Furthermore, the effect of prior ECs on sarcolemmal GLUT-4 protein content in plasma membrane (PM) vesicles isolated from contraction-stimulated muscle was determined. Rat gastrocnemius muscle was electrically stimulated for ECs, and the contralateral muscle served, as unstimulated control (UC). Two days later, the total GLUT-4 protein content was decreased by 50% (P < 0.05) and 32% (P < 0.05) in the white and red gastrocnemius muscle, respectively. Furthermore, the GLUT-4 mRNA concentration was decreased by 41% (P < 0.05) in both the white and red gastrocnemius muscle. Moreover, the GLUT-4 transcription rate, determined by nuclear run-on analysis, was decreased by 75% (P < 0.05) in mixed EC gastrocnemius muscle compared with UC muscle. PM vesicles were isolated from EC and UC muscle after 15 min of isometric contractions. The PM GLUT-4 protein content was reduced by 51% (P < 0.05) in EC muscle compared with UC muscle. In conclusion, 2 days after ECs, the GLUT-4 transcription rate, GLUT-4 mRNA, and GLUT-4 protein content were decreased in rat skeletal muscle. Moreover, the PM GLUT-4 protein content in contraction-stimulated muscle was decreased. We suggest that eccentric muscle contractions decrease muscle GLUT-4 transcription rate, resulting in a lower GLUT-4 protein content, which in turn decreases the number of GLUT-4 transporters translocated to the sarcolemma, ultimately leading to decreased contraction-induced muscle glucose transport.

Progressive increase in glucose transport and GLUT-4 in human sarcolemmal vesicles during moderate exercise

Muscle glucose uptake increases progressively during moderate-intensity exercise. To elucidate whether this is due to a progressive increase in sarcolemmal glucose transport capacity, nine men exercised for 40 min at 75% maximal oxygen uptake on a bicycle ergometer. Muscle biopsies were obtained from the vastus lateralis at rest (0 min) and after 5 and 40 min of exercise and used for production of sarcolemmal giant (SG) vesicles. SG vesicle glucose transport at 5 mM increased (P < 0.05) by 38 and 93% after 5 and 40 min of exercise, respectively, compared with glucose transport at rest. The SG vesicle GLUT-4 protein content increased (P < 0.05) by 36 and 91% after 5 and 40 min of exercise, respectively, compared with rest. Thus the increase in vesicle glucose transport was accompanied by a similar increase in SG vesicle GLUT-4 protein content. Muscle glucose and glucose 6-phosphate were low at rest, increased (P < 0.05) 2.2- and 2.3-fold, respectively, after 5 min of exercise, and returned to resting values after 40 min of exercise. It is concluded that the progressive increase in muscle glucose uptake during moderate-intensity exercise may be due at least in part to a progressive increase in sarcolemmal glucose transport and GLUT-4 protein content.

Membrane associated fatty acid binding protein (FABPpm) in human skeletal muscle is increased by endurance training

Endurance training increases the capacity for utilization of fatty acids. Since fatty acids are believed to enter cells via facilitated diffusion a possible mechanism behind this adaptation to training might be a training-induced increase in membrane content of putative fatty acid transporters. We investigated whether the expression of the 40 KD membrane associated fatty acid binding protein (FABPpm) in skeletal muscle is increased with endurance training in man. The FABPpm was detectable in a crude membrane preparation from human skeletal muscle. Three weeks of intense one-legged endurance training increased (p < 0.05) the content of FABPpm by 49% whereas in the untrained control muscle no change was observed. In addition, the activity of citrate synthase was increased (p < 0.05) by 20% in the trained compared with the untrained muscle. It is concluded that expression of FABPpm in human skeletal muscle is increased with endurance training consistent with a role of FABPpm as a sarcolemmal fatty acid transporter.

Decreased muscle GLUT-4 and contraction-induced glucose transport after eccentric contractions

Eccentric exercise causes muscle damage and decreased muscle glycogen and glucose transporter isoform (GLUT-4) protein content. We investigated whether the contraction-induced increase in skeletal muscle glucose transport and muscle performance is affected by prior eccentric contractions. The calf muscles from rats were stimulated for eccentric (EC) or concentric (CC) contractions or were passively stretched (ST). Muscles from unstimulated control (CT) rats were also studied. Two days later, all rats had their isolated hindlimbs perfused either at rest or during 15 min of isometric muscle contractions. EC rats had a significantly lower total GLUT-4 protein content in the white gastrocnemius (GW) muscle (55%) and red gastrocnemius (GR) muscle (34%) compared with muscle from the CT, ST, and CC rats. In contrast, GLUT-1 protein content was approximately twofold higher in the GW muscle in EC rats than in CT rats. In the GW and GR muscle, prior eccentric exercise decreased contraction-induced stimulation of glucose transport compared with CT, ST, and CC rats despite no difference in tension development and oxygen uptake among the groups. There was no change in total GLUT-4 content and glucose transport in the soleus (S) muscle among the four group. It is concluded that the GLUT-4 and GLUT-1 protein contents in fast-twitch muscle are decreased and increased, respectively, 2 days after eccentric contractions. The functional consequence of these changes appears to be decreased contraction-induced increase in skeletal muscle glucose transport.

Eccentric exercise decreases maximal insulin action in humans: muscle and systemic effects

1. Unaccustomed eccentric exercise decreases whole-body insulin action in humans. To study the effects of one-legged eccentric exercise on insulin action in muscle and systemically, the euglycaemic clamp technique combined with arterial and bilateral femoral venous catheterization was used. Seven subjects participated in two euglycaemic clamps, performed in random order. One clamp was preceded 2 days earlier by one-legged eccentric exercise (post-eccentric exercise clamp (PEC)) and one was without the prior exercise (control clamp (CC)). 2. During PEC the maximal insulin-stimulated glucose uptake over the eccentric thigh was marginally lower when compared with the control thigh, (11.9%, 64.6 +/- 10.3 vs. 73.3 +/- 10.2 mumol kg-1 min-1, P = 0.08), whereas no inter-thigh difference was observed at a submaximal insulin concentration. The glycogen concentration was lower in the eccentric thigh for all three clamp steps used (P < 0.05). The glucose transporter GLUT4 protein content was on average 39% lower (P < 0.05) in the eccentric thigh in the basal state, whereas the maximal activity of glycogen synthase was identical in the two thighs for all clamp steps. 3. The glucose infusion rate (GIR) necessary to maintain euglycaemia during maximal insulin stimulation was lower during PEC compared with CC (15.7%, 81.3 +/- 3.2 vs. 96.4 +/- 8.8 mumol kg-1 min-1, P < 0.05). 4. Our data show that 2 days after unaccustomed eccentric exercise, muscle and whole-body insulin action is impaired at maximal but not submaximal concentrations. The local effect cannot account for the whole-body effect, suggesting the release of a factor which decreases insulin responsiveness systemically.

Effect of vanadate on glucose transporter (GLUT4) intrinsic activity in skeletal muscle plasma membrane giant vesicles

Maximally effective concentrations of vanadate (a phosphotyrosine phosphatase inhibitor) increase glucose transport in muscle less than maximal insulin stimulation. This might be due to vanadate-induced decreased intrinsic activity of GLUT4 accompanying GLUT4 translocation. Thus, the effect of vanadate (NaVO3) on glucose transporter (GLUT4) intrinsic activity (V(max) = intrinsic activity x [GLUT4 protein]) was studied in muscle plasma membrane giant vesicles. Giant vesicles (average diameter 7.6 microns) were produced by collagenase treatment of rat skeletal muscle. The vesicles were incubated for 1.5 h with concentrations of vanadate ranging from 3 to 40 mmol l-1 at 34 degrees C before being used for determination of glucose transport. The dose-response curve showed that vanadate decreased the specific D-glucose uptake by a maximum of 70% compared with a control preparation. The vanadate-induced decrease in glucose uptake was not due to a decrease in number of vesicles. To further verify the apparent vanadate-induced decrease in GLUT4 intrinsic activity, the kinetics of glucose transport were also examined. In the presence of 10 mmol l-1 vanadate the V(max) and K(m) were decreased (P < 0.05, n = 6) 55% and 60%, respectively, compared with control. The plasma membrane GLUT4 protein content was not changed in response to vanadate. It is concluded that vanadate decreased glucose transport per GLUT4 (intrinsic activity). This finding suggests that regulation of glucose transport in skeletal muscle can involve changes in GLUT4 intrinsic activity.

Exercise-induced increase in glucose transport, GLUT-4, and VAMP-2 in plasma membrane from human muscle

A major effect of muscle contractions is an increase in sarcolemmal glucose transport. We have used a recently developed technique to produce sarcolemmal giant vesicles from human muscle biopsy samples obtained before and after exercise. Six men exercised for 10 min at 50% maximal O2 uptake (Vo2max) and then to fatigue at 100% Vo2max (5.7 +/- 0.2 min). Vesicle glucose transport at 5 mM increased from 3.3 +/- 0.6 pmol.microgram-1.min-1 at rest to 6.6 +/- 1.0 pmol.microgram-1.min-1 at fatigue (mean +/- SE, n = 6, P < 0.05). This increase in glucose transport was associated with a 1.6-fold increase in vesicle GLUT-4 protein content. Glucose transport normalized to GLUT-4 protein content also increased with exercise, suggesting increased intrinsic activity of GLUT-4. Furthermore, exercise resulted in a 1.4-fold increase in sarcolemmal vesicle-associated membrane protein (VAMP-2) content, suggesting that muscle contractions may induce trafficking of GLUT-4-containing vesicles via a mechanism similar to neurotransmitter release. Our results demonstrate for the first time exercise-induced translocation of GLUT-4 and VAMP-2 to the plasma membrane of human muscle and increased sarcolemmal glucose transport.

Eccentric muscle damage transiently decreases rat skeletal muscle GLUT-4 protein

The effects of concentric and muscle-damaging eccentric contractions on muscle glucose transporter GLUT-4 content were studied in rat muscles. Rats were anesthetized, the calf muscles on one side were stimulated electrically for concentric or eccentric contractions, and bilateral calf muscles were obtained in the postexercise period. Inflammatory and phagocytic cells accumulated in the eccentric white and red gastrocnemius muscles, whereas there were only discrete changes in the eccentric soleus. Glycogen was depleted to the same extent in the white and red gastrocnemius muscles after both types of stimulation, and it remained decreased > 2 days in eccentric muscles. The total GLUT-4 protein content was decreased in the eccentric white and red gastrocnemius muscles 1 and 2 days after the eccentric stimulation, whereas the maximal activity of glycogen synthase was unaffected at these time points. In conclusion, our one-legged stimulation model caused eccentric muscle damage in the white and red gastrocnemius, whereas only minor damage was observed in the soleus muscle. In damaged muscle, muscle glycogen and GLUT-4 protein content were decreased for > 2 days. These findings may suggest (but do not prove) that decreased muscle GLUT-4 protein is involved in the delayed glycogen resynthesis after eccentric exercise.

Kinetics of lactate transport in sarcolemmal giant vesicles obtained from human skeletal muscle

We developed a method that allows the measurement of muscle lactate transport in humans. The transport studies were carried out with giant (1.8- to 36-microns-diam) sarcolemmal vesicles obtained by collagenase treatment of needle biopsy material. Marker enzyme analyses demonstrated that the vesicular membrane is predominantly of sarcolemmal origin, contamination with sarcoplasmic reticulum membranes is very low, and mitochondrial membranes are not a major contaminant. The vesicles were loaded with labeled lactate, and the efflux was measured. The system displayed saturation kinetics and inhibitor sensitivity. In equilibrium exchange experiments (pH 7.4, 21 degrees C), the Michaelis-Menten constant (Km) for the carrier-mediated flux was 30 +/- 8 (SD) mM and maximal transport rate (Vmax) was 184 +/- 24 pmol.cm-2.s-1 (142 nmol.mg protein-1.min-1). In zero-trans efflux experiments, Km was 24 +/- 8 mM and Vmax was 81 +/- 11 pmol.cm-2.s-1 (63 nmol.mg protein-1.min-1). In infinite-cis experiments with a variable lactate concentration on the outside of the vesicles, Km was 8 +/- 4 mM and Vmax was 136 +/- 9 pmol.cm-2.s-1 (105 nmol.mg protein-1.min-1). Thus, the system displayed transacceleration. Low pH (6.4) had no significant effect on equilibrium exchange experiments, whereas in zero-trans experiments low pH at the trans side inhibited the flux by 50%. We concluded that lactate transport can be studied in giant vesicles obtained from a single human muscle biopsy. Our data provide evidence for the existence of a lactate carrier in human sarcolemma. This transport system must be taken into account in models of human lactate kinetics.

Effect of glucose-6-phosphate and pH on glucose transport in skeletal muscle plasma membrane giant vesicles

The effect of glucose-6-phosphate (G-6-P) and pH on glucose transport was studied in skeletal muscle plasma membrane giant vesicles containing GLUT4 but not GLUT1. Vesicles (average diameter 7.6 microns) were obtained by collagenase treatment of muscle. The vesicles were incubated with 10 mmol l-1 G-6-P and, after 0.5 and 2 h of incubation, the intravesicular G-6-P concentration was 0.93 +/- 0.4 mmol l-1 and 1.18 +/- 0.5 mmol l-1 (mean +/- SE, n = 4), respectively. In order to increase the intravesicular G-6-P concentration, 0.001% saponin was added during incubation, which increased the 2-h intravesicular G-6-P concentration to 4.57 +/- 1.0 mmol l-1 (n = 4). Initially, vesicles were used for glucose transport studies after 30 min of incubation with 10 mmol l-1 of G-6-P. There was no effect of G-6-P on either the affinity constant (Km) or maximal velocity (Vmax) of the glucose transport. Subsequently, vesicles were incubated for 2 h with 10 mmol l-1 of G-6-P and 0.001% saponin. Still no effect of G-6-P on glucose transport could be detected. In contrast, the rate of D-glucose transport was affected, when extravesicular pH was varied from 6.0 to 7.8. The maximum glucose transport rate was found at pH 7.2 and was decreased at both higher and lower pH. It is concluded that G-6-P has no effect on GLUT4 intrinsic activity in rat skeletal muscle plasma membrane. In contrast, GLUT4 intrinsic activity is sensitive to changes in pH.

Glucose transport and transporters in muscle giant vesicles: differential effects of insulin and contractions

Collagenase treatment of skeletal muscle results in the formation of large spheres of membranes (3-30 microns diam). A procedure is described for purification and concentration of these giant membrane vesicles prepared from rat muscle. Morphological observations, marker enzyme analysis, and immunoblotting demonstrate that the vesicles are of plasma membrane origin and that sarcoplasmic reticulum, T-tubules, and mitochondrial inner membranes are absent from the preparation. Western blots demonstrate that the vesicles contain GLUT-4 glucose transporters, whereas GLUT-1 could not be detected. Vesicles prepared from control muscle display specific transport of D-glucose with a maximum velocity (Vmax) for glucose influx of approximately 2,500 pmol.mg plasma membrane protein-1.s-1 and an apparent Michaelis constant (Km) of 16 mM measured at zero-trans conditions at room temperature. Muscle contractions in vivo doubled the Vmax of vesicle glucose transport and membrane GLUT-4 content but did not change Km. In contrast, in vivo administration of insulin did not affect vesicle glucose transport or membrane GLUT-4 content. The combination of insulin and contractions caused similar changes as did contractions alone. It is concluded that the present vesicle population contains membrane components almost exclusively derived from the plasma membrane and contains very little if any GLUT-1 but substantial amounts of GLUT-4. Thus the preparation allows the study of transport kinetics of pure GLUT-4 transporters. The procedure for preparing vesicles probably results in activation of the glucose transport system similar to the activation by insulin but not by contractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Fansimef for prophylaxis of malaria: a double-blind randomized placebo controlled trial

At a time when Fansimef, the fixed combination of mefloquine, sulfadoxine and pyrimethamine was considered for prophylaxis of falciparum malaria, a randomized double-blind study comparing the efficacy and tolerability of Fansimef with that of Lariam (mefloquine), Fansidar, chloroquine and placebo in malaria prophylaxis was performed in Thailand from July 1987 to January 1988. The study population of 602 adult males was recruited in Pak Tongchai District, some 360 km North-East of Bangkok, where multiresistant P. falciparum is endemic. All active treatments and placebo were given once weekly for 24 weeks with doses as follows: Fansimef: 125 mg mefloquine + 250 mg sulfadoxine + 12.5 mg pyrimethamine (1 half-strength tablet); Lariam: 125 mg mefloquine (1 half-strength tablet); Fansidar: 500 mg sulfadoxine + 25 mg pyrimethamine; chloroquine; 300 mg. A loading dose of 2 half-strength tablets was given in the Fansimef group in weeks 1 and 2 and in the Lariam group in weeks 1 to 4. The incidence of acute episodes of P. falciparum per 100 person months of prophylaxis was 0.17 each in the Fansimef and the Lariam groups, 1.18 in the Fansidar group, 0.69 in the chloroquine group and 0.64 in the placebo group (differences statistically not significant). Clinically adverse events were reported by 170 subjects (Fansimef 28, Lariam 29, Fansidar 41, choroquine 43, placebo 29; differences statistically not significant). The most frequent adverse events in all groups were headache, sleepiness, dizziness and weakness.(ABSTRACT TRUNCATED AT 250 WORDS)

A statistical procedure for the estimation of accuracy parameters in interlaboratory studies

Interlaboratory studies are conducted to estimate the accuracy of methods of laboratory measurements. The standard parameters used to describe this accuracy are the repeatability and the reproducibility. Usually variance components models are used to estimate these parameters. If the model assumptions are violated the resulting estimates for reproducibility and repeatability may, however, be biased. A new method of residual analysis in variance components models--developed by the author--may be used to detect violations of the model assumptions. If the residual analysis indicates that the model assumptions are violated, a simple robust method--which makes fewer assumptions--may be used for the estimation of accuracy parameters. The application of this residual analysis is demonstrated using data of an interlaboratory study. Graphical methods play an important role in the evaluation of the residuals. The analysis of the residuals uses methods similar to those used for the analysis of Studentized residuals in the linear model. The estimates obtained by the variance components model and the simple robust method are compared. The results of the residual analysis may be used to decide which of the two estimates can be considered more appropriate. The necessity of residual analysis in the analysis of interlaboratory studies by variance components models is pointed out. Potential hazards inherent to residual analysis in variance components models are discussed. Conclusions for the analysis of interlaboratory studies are drawn.

Effect of adaptation and wavelength on the power spectrum of human oscillatory potentials

Oscillatory potentials were recorded from four adult subjects under dark- and light-adapted conditions with photopically balanced red and blue flashes. The responses between 80 and 200 Hz were analyzed by means of a Fast Fourier transform program. The results show a robust change in the power--but not in the frequency composition--with the different stimulus conditions. We suggest that an analysis of the total power within this frequency band may provide a quantitative way of evaluating the duplex nature of the oscillatory potentials.

Biliary excretion of bisacodyl and picosulphate in man: studies in gallstone patients after biliary tract surgery

Bisacodyl (=BIS) and picosulphate (=PICO) have been given perorally to postoperative gallstone patients, who have undergone biliary tract surgery with the insertion of an indwelling T-tube. The doses corresponded to 7.7 mg of their common free diphenol desacetylbisacodyl (=DES). The bile was sampled in hourly fraction from the external limb of the T-tube; these fractions were analysed by a modification of the HPLC method previously used to study biliary excretion in the rat. In the BIS-patients (n=8), DES in conjugated form occurred in significant concentration already in the first fractions; peak excretion values equivalent to 4-8 microgram DES/ml bile were reached in 2-5 hours. Unchanged BIS could not be detected, and the concentration levels of unconjugated DES were insignificant. The PICO-patients (n=8) on the other hand showed low DES concentrations (conjugated + free less than or equal to 0.5 microgram DES/ml) in all fractions, or low initial concentrations followed by a more or less pronounced rise in the later fractions. These results are, qualitatively, as in the rat. However, the dose fractions excreted in bile (assuming a total hepatic output of 50ml/hours) seem smaller than those to be expected from rat experiments, at least as far as BIS is concerned.

Enterohepatic circulation, urinary excretion and laxative action of some bisacodyl derivatives after intragastric administration in the rat

Bisacodyl (BIS), the parent diphenol (DES) and its sulphuric acid di-ester (picosulphate = PICO) were given by stomach tube to fasted rats at a dose of 3.1 mumol/100 g rat. Bile was sampled in the periods 0-6, 6-12 and 12-18 hrs after drug administration, and assayed for total diphenol (= free + conjugated) by HPLC. Mean fractions (% of dose +/- S.E.M.) excreted in 5 rats per compound and period were: BIS 74.0 +/- 4.7, 51.9 +/- 7.9 and 30.8 +/- 2.5; DES 41.2 +/-4.3, 46.8 +/- 4.7 and 25.1 +/- 2.5; PICO 9.0 +/- 0.9, 26.0 +/- 5.4 and 19.6 +/- 3.1. Only minor amounts were excreted as free diphenol. Urine samples taken by bladder puncture and assayed as above furthermore showed that the renal excretion of total diphenol was insignificant compared to the amounts excreted in bile. Practically no diphenol was present in urine 0-6 hrs after the administration of PICO. In experiments with BIS and DES at 0.85 mumol/100 g, total diphenol excreted in bile during 0-6 hrs was: BIS 67.1 +/- 2.6 (n = 5); DES: 55.4 +/- 3.0 (5). - The latency time for laxative effect was studied in groups of 10 unfasted rats per compound. cumulative time response curves showed that PICO caused diarrhoea more promptly at 0.85 mumol/100 g than either BIS or DES. In most rats, this delayed action of BIS and DES persisted also at 1.7 mumol/100 g. At 3.1 mumol/100 g, however, the majority of the rats reacted as promptly to these two compounds as to PICO. These results are discussed in relation to the biliary excretion experiments, and interpreted in terms of the relative importance at the different dose levels of: 1. The enterohepatic recirculated fraction, and 2. The non-absorbed fraction, which passes directly to the large intestine. For PICO, the latter fraction is the single determinant of the effect, which is triggered when the di-ester is being hydrolyzed to active diphenol in this part of the GI-tract.