Skin temperature is sensed by peripheral thermoreceptors. Using the neuronal soma in primary culture as a model of the receptor terminal, we have investigated the mechanisms of cold transduction in thermoreceptive neurones from rat dorsal root ganglia. Cold‐sensitive neurones were pre‐selected by screening for an increase in [Ca²⁺]_ion cooling; 49 % of them were also excited by 0.5 μmcapsaicin. Action potentials and voltage‐gated currents of cold‐sensitive neurones were clearly distinct from those of cold‐insensitive neurones. All cold‐sensitive neurones expressed an inward current activated by cold and sensitised by (‐)‐menthol, which was absent from cold‐insensitive neurones. This current was carried mainly by Na⁺ions and caused a depolarisation on cooling accompanied by action potentials, inducing voltage‐gated Ca²⁺entry; a minor fraction of Ca²⁺entry was voltage‐independent. Application of (‐)‐menthol shifted the threshold temperatures of the cold‐induced depolarisation and the inward current to the same extent, indicating that the cold‐ and menthol‐activated current normally sets the threshold temperature for depolarisation during cooling. The action of menthol was stereospecific, with the (+)‐isomer being a less effective agonist than the (‐)‐isomer. Extracellular Ca²⁺modulated the cold‐ and menthol‐activated current in a similar way to its action on intact cold receptors: lowered [Ca²⁺]_osensitised the current, while raised [Ca²⁺]_oantagonised the menthol‐induced sensitisation. During long cooling pulses the current showed adaptation, which depended on extracellular Ca²⁺and was mediated by a rise in [Ca²⁺]_i. This adaptation consisted of a shift in the temperature sensitivity of the channel. In capsaicin‐sensitive neurones, capsaicin application caused a profound depression of the cold‐activated current. Inclusion of nerve growth factor in the culture medium shifted the threshold of the cold‐activated current towards warmer temperatures. The current was blocked by 50 μmcapsazepine and 100 μmSKF 96365. We conclude that the cold‐ and menthol‐activated current is the major mechanism responsible for cold‐induced depolarisation in DRG neurones, and largely accounts for the known transduction properties of intact cold receptors.

Background: A structural, electrical and metabolic atrial remodeling is central in the development of atrial fibrillation (AF) contributing to its initiation and perpetuation. In the heart, HDACs (histone deacetylases) control remodeling associated processes like hypertrophy, fibrosis, and energy metabolism. Here, we analyzed, whether the HDAC class I/IIa inhibitor valproic acid (VPA) is able to attenuate atrial remodeling in CREM-IbΔC-X (cAMP responsive element modulator isoform IbΔC-X) transgenic mice, a mouse model of extensive atrial remodeling with age-dependent progression from spontaneous atrial ectopy to paroxysmal and finally long-lasting AF. Methods: VPA was administered for 7 or 25 weeks to transgenic and control mice. Atria were analyzed macroscopically and using widefield and electron microscopy. Action potentials were recorded from atrial cardiomyocytes using patch-clamp technique. ECG recordings documented the onset of AF. A proteome analysis with consecutive pathway mapping identified VPA-mediated proteomic changes and related pathways. Results: VPA attenuated many components of atrial remodeling that are present in transgenic mice, animal AF models, and human AF. VPA significantly ( P <0.05) reduced atrial dilatation, cardiomyocyte enlargement, atrial fibrosis, and the disorganization of myocyte’s ultrastructure. It significantly reduced the occurrence of atrial thrombi, reversed action potential alterations, and finally delayed the onset of AF by 4 to 8 weeks. Increased histone H4-acetylation in atria from VPA-treated transgenic mice verified effective in vivo HDAC inhibition. Cardiomyocyte-specific genetic inactivation of HDAC2 in transgenic mice attenuated the ultrastructural disorganization of myocytes comparable to VPA. Finally, VPA restrained dysregulation of proteins in transgenic mice that are involved in a multitude of AF relevant pathways like oxidative phosphorylation or RhoA (Ras homolog gene family, member A) signaling and disease functions like cardiac fibrosis and apoptosis of muscle cells. Conclusions: Our results suggest that VPA, clinically available, well-tolerated, and prescribed to many patients for years, has the therapeutic potential to delay the development of atrial remodeling and the onset of AF in patients at risk.

The effects of two pyrethroids on recombinant wild-type and mutant (pyrethroid-resistant) Na⁺ channels of Drosophila melanogaster have been studied. Three mutations that confer resistance (kdr/superkdr) to pyrethroids were inserted, either individually or in combination, into the para Na⁺ channel of D. melanogaster: L1014F in domain IIS6, M918T in the IIS4-S5 linker, and T929I in domain IIS5. Channels were expressed in Xenopus laevis oocytes and the effects of the pyrethroids permethrin (type I) and deltamethrin (type II) on Na⁺ currents were investigated using voltage clamp. The Na⁺ channels deactivated slowly after deltamethrin treatment, the resultant “tail” currents being used to quantify the effects of this pyrethroid. The Hill slope of 2 for deltamethrin action on the wild-type channel and the mutant L1014F channel is indicative of cooperative binding at two or more sites on these channels. In contrast, binding to the mutants M918T and T929I is noncooperative. Tail currents for the wild-type channel and L1014F channel decayed biphasically, whereas those for M918T and T929I mutants decayed monophasically. The L1014F mutant was ∼20-fold less sensitive than the wild-type to deltamethrin. Surprisingly, the sensitivity of the double mutant M918T+L1014F to deltamethrin was similar to that of M918T alone, whereas the sensitivity of T929I+L1014F was >30,000-fold lower than that of T929I. Permethrin was less potent than deltamethrin, and its binding to all channel types was noncooperative. The decays of permethrin-induced tail currents were exclusively monophasic. These findings are discussed in terms of the properties and possible locations of pyrethroid binding sites on the D. melanogaster Na⁺ channel.

Hypertension is a major risk factor for atrial fibrillation. We hypothesized that arterial hypertension would alter atrial myocyte calcium (Ca²⁺) handling and that these alterations would serve to trigger atrial tachyarrhythmias. Left atria or left atrial (LA) myocytes were isolated from spontaneously hypertensive rats (SHR) or normotensive Wistar-Kyoto (WKY) controls. Early after the onset of hypertension, at 3 months of age, there were no differences in Ca²⁺ transients (CaTs) or expression and phosphorylation of Ca²⁺ handling proteins between SHR and WKY. At 7 months of age, when left ventricular (LV) hypertrophy had progressed and markers of fibrosis were increased in left atrium, CaTs (at 1 Hz stimulation) were still unchanged. Subcellular alterations in Ca²⁺ handling were observed, however, in SHR atrial myocytes including (i) reduced expression of the α1C subunit of and reduced Ca²⁺ influx through L-type Ca²⁺ channels, (ii) reduced expression of ryanodine receptors with increased phosphorylation at Ser2808, (iii) decreased activity of the Na⁺/Ca²⁺ exchanger (at unaltered intracellular Na⁺ concentration), and (iv) increased SR Ca²⁺ load with reduced fractional release. These changes were associated with an increased propensity of SHR atrial myocytes to develop frequency-dependent, arrhythmogenic Ca²⁺ alternans. In SHR, hypertension induces early subcellular LA myocyte Ca²⁺ remodelling during compensated LV hypertrophy. In basal conditions, atrial myocyte CaTs are not changed. At increased stimulation frequency, however, SHR atrial myocytes become more prone to arrhythmogenic Ca²⁺ alternans, suggesting a link between hypertension, atrial Ca²⁺ homeostasis, and development of atrial tachyarrhythmias.

Arterial hypertension affects ≈ 1 billion people worldwide. It is associated with increased morbidity and mortality and responsible for millions of deaths each year. Hypertension mediates damage of target organs including the heart. In addition to eliciting left ventricular hypertrophy, dysfunction and heart failure, hypertension also causes left atrial remodeling that may culminate in atrial contractile dysfunction and atrial fibrillation. Here, we will summarize data on the various aspects of left atrial remodeling in (essential) hypertension gathered from studies on patients with hypertension and from spontaneously hypertensive rats, an animal model that closely mimics cardiac remodeling in human hypertension. Analyzing the timeline of remodeling processes, i.e., distinguishing between alterations occurring in prehypertension, in early hypertension and during advanced hypertensive heart disease, we will derive the potential mechanisms underlying left atrial remodeling in (essential) hypertension. Finally, we will discuss the consequences of these remodeling processes for atrial and ventricular function. The data imply that left atrial remodeling is multifactorial, starts early in hypertension and is an important contributor to the progression of hypertensive heart disease, including the development of atrial fibrillation and heart failure.