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Abstract: Epidemiological, clinical and experimental studies suggest that the cardioprotective effect of fish intake is mainly due to the antiarrhythmic properties of marine n-3 polyunsaturated fatty acids (PUFA), which modulate ion currents. Emerging evidences point to similar effects of α-linolenic acid (ALA), a vegetable n-3 PUFA, but much less is known about its effects on the specific cardiac ion channels. Using electrophysiology, protein biochemistry and fluorescence anisotropy measurements, we tested the effects of ALA on the atrial specific Kv1.5 channel. In stably transfected Ltk − cells, ALA blocked Kv1.5 channels in a time- and voltage-dependent manner with an IC50 value of 3.7±0.3 μM. ALA at 2.5 μM inhibited the Kv1.5 current, shifted the midpoint of the activation curve by −8.8±4.3 mV (p <0.05), accelerated the activation kinetics of Kv1.5 due to a negative shift in its voltage dependency and slowed its deactivation process. Marine n-3 PUFA eicosapentaenoic and docosahexaenoic (EPA and DHA) acids, but not ALA, reduced the steady-state levels of Kv1.5 protein. DHA, but not ALA, increased the cell membrane order parameter. These results demonstrate that ALA directly blocks atria-specific Kv1.5 channels without modifying their expression or the bilayer order. Together, these effects suggest that the antiarrhythmic potential of diets enriched with plant-derived n-3 PUFA result, in part, from direct effects on cardiac ion channels. [Copyright &y& Elsevier]

Abstract: There is an increasing awareness of immune cell modulation by antimicrobial peptides. While this process often requires specific receptors for the peptides involved, several reports point out to a receptor-independent process. The cecropin A–melittin hybrid peptide CA(1–8)M(1–18) (KWKLFKKIGIGAVLKVLTTGLPALIS-amide) modifies gene expression in the macrophage line RAW 264.7 in the absence of any previous macrophage priming, suggesting a membrane permeation process. To further analyze the initial steps of this mechanism, we have studied the interaction of the peptide with these cells. Below 2 μM, CA(1–8)M(1–18) causes a concentration-dependent membrane depolarization partially reversible with time. At 2 μM, the accumulation of the SYTOX green vital dye is one half of that achieved with 0.05% Triton X-100. The binding level, as assessed by fluorescein-labeled CA(1–8)M(1–18), varies from 7.7±1.2 to 37.4±3.9×106 molecules/cell over a 0.5–4.0 μM concentration range. Electrophysiological experiments with 0.5 μM CA(1–8)M(1–18), a concentration that triggers maximal NOS2 expression and minimal toxicity, show a reversible current induction in the RAW 264.7 plasma membrane that is maintained as far as peptide is present. This activation of the macrophage involves the production of nitric oxide, a metabolite lethal for many pathogens that results from unspecific membrane permeation by antimicrobial peptides, and represents a new mode of action that may open new therapeutic possibilities for these compounds against intracellular pathogens. [Copyright &y& Elsevier]