Re-Evaluation of the Action Potential Upstroke Velocity as a Measure of the Na+ Current in Cardiac Myocytes at Physiological Conditions

Background: The SCN5A encoded sodium current (INa) generates the action potential (AP) upstroke and is a major determinant of AP characteristics and AP propagation in cardiac myocytes. Unfortunately, in cardiac myocytes, investigation of kinetic properties of INa with near-physiological ion concentrations and temperature is technically challenging due to the large amplitude and rapidly activating nature of INa, which may seriously hamper the quality of voltage control over the membrane. We hypothesized that the alternating voltage clamp-current clamp (VC/CC) technique might provide an alternative to traditional voltage clamp (VC) technique for the determination of INa properties under physiological conditions. Principal Findings: We studied INa under close-to-physiological conditions by VC technique in SCN5A cDNA-transfected HEK cells or by alternating VC/CC technique in both SCN5A cDNA-transfected HEK cells and rabbit left ventricular myocytes. In these experiments, peak INa during a depolarizing VC step or maximal upstroke velocity, dV/dtmax, during VC/CC served as an indicator of available INa. In HEK cells, biophysical properties of INa, including current density, voltage dependent (in)activation, development of inactivation, and recovery from inactivation, were highly similar in VC and VC/CC experiments. As an application of the VC/CC technique we studied INa in left ventricular myocytes isolated from control or failing rabbit hearts

Measuring serotonin synthesis: from conventional methods to PET tracers and their (pre)clinical implications

The serotonergic system of the brain is complex, with an extensive innervation pattern covering all brain regions and endowed with at least 15 different receptors (each with their particular distribution patterns), specific reuptake mechanisms and synthetic processes. Many aspects of the functioning of the serotonergic system are still unclear, partially because of the difficulty of measuring physiological processes in the living brain. In this review we give an overview of the conventional methods of measuring serotonin synthesis and methods using positron emission tomography (PET) tracers, more specifically with respect to serotonergic function in affective disorders. Conventional methods are invasive and do not directly measure synthesis rates. Although they may give insight into turnover rates, a more direct measurement may be preferred. PET is a noninvasive technique which can trace metabolic processes, like serotonin synthesis. Tracers developed for this purpose are α-[11C]methyltryptophan ([11C]AMT) and 5-hydroxy-L-[β-11C]tryptophan ([11C]5-HTP). Both tracers have advantages and disadvantages. [11C]AMT can enter the kynurenine pathway under inflammatory conditions (and thus provide a false signal), but this tracer has been used in many studies leading to novel insights regarding antidepressant action. [11C]5-HTP is difficult to produce, but trapping of this compound may better represent serotonin synthesis. AMT and 5-HTP kinetics are differently affected by tryptophan depletion and changes of mood. This may indicate that both tracers are associated with different enzymatic processes. In conclusion, PET with radiolabelled substrates for the serotonergic pathway is the only direct way to detect changes of serotonin synthesis in the living brain

The primary headaches: genetics, epigenetics and a behavioural genetic model

The primary headaches, migraine with (MA) and without aura (MO) and cluster headache, all carry a substantial genetic liability. Familial hemiplegic migraine (FHM), an autosomal dominant mendelian disorder classified as a subtype of MA, is due to mutations in genes encoding neural channel subunits. MA/MO are considered multifactorial genetic disorders, and FHM has been proposed as a model for migraine aetiology. However, a review of the genetic studies suggests that the FHM genes are not involved in the typical migraines and that FHM should be considered as a syndromic migraine rather than a subtype of MA. Adopting the concept of syndromic migraine could be useful in understanding migraine pathogenesis. We hypothesise that epigenetic mechanisms play an important role in headache pathogenesis. A behavioural model is proposed, whereby the primary headaches are construed as behaviours, not symptoms, evolutionarily conserved for their adaptive value and engendered out of a genetic repertoire by a network of pattern generators present in the brain and signalling homeostatic imbalance. This behavioural model could be incorporated into migraine genetic research

Effects of Anacetrapib in Patients with Atherosclerotic Vascular Disease

BACKGROUND: Patients with atherosclerotic vascular disease remain at high risk for cardiovascular events despite effective statin-based treatment of low-density lipoprotein (LDL) cholesterol levels. The inhibition of cholesteryl ester transfer protein (CETP) by anacetrapib reduces LDL cholesterol levels and increases high-density lipoprotein (HDL) cholesterol levels. However, trials of other CETP inhibitors have shown neutral or adverse effects on cardiovascular outcomes. METHODS: We conducted a randomized, double-blind, placebo-controlled trial involving 30,449 adults with atherosclerotic vascular disease who were receiving intensive atorvastatin therapy and who had a mean LDL cholesterol level of 61 mg per deciliter (1.58 mmol per liter), a mean non-HDL cholesterol level of 92 mg per deciliter (2.38 mmol per liter), and a mean HDL cholesterol level of 40 mg per deciliter (1.03 mmol per liter). The patients were assigned to receive either 100 mg of anacetrapib once daily (15,225 patients) or matching placebo (15,224 patients). The primary outcome was the first major coronary event, a composite of coronary death, myocardial infarction, or coronary revascularization. RESULTS: During the median follow-up period of 4.1 years, the primary outcome occurred in significantly fewer patients in the anacetrapib group than in the placebo group (1640 of 15,225 patients [10.8%] vs. 1803 of 15,224 patients [11.8%]; rate ratio, 0.91; 95% confidence interval, 0.85 to 0.97; P=0.004). The relative difference in risk was similar across multiple prespecified subgroups. At the trial midpoint, the mean level of HDL cholesterol was higher by 43 mg per deciliter (1.12 mmol per liter) in the anacetrapib group than in the placebo group (a relative difference of 104%), and the mean level of non-HDL cholesterol was lower by 17 mg per deciliter (0.44 mmol per liter), a relative difference of -18%. There were no significant between-group differences in the risk of death, cancer, or other serious adverse events. CONCLUSIONS: Among patients with atherosclerotic vascular disease who were receiving intensive statin therapy, the use of anacetrapib resulted in a lower incidence of major coronary events than the use of placebo. (Funded by Merck and others; Current Controlled Trials number, ISRCTN48678192 ; ClinicalTrials.gov number, NCT01252953 ; and EudraCT number, 2010-023467-18 .)