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Abstract: Voltage-gated sodium channels (Nav) consist of a pore-forming α subunit (Navα) associated with β regulatory subunits (Navβ). Adult skeletal myocytes primarily express Nav1.4 channels. We found, however, using neonatal L6E9 myocytes, that myofibers acquire a Nav1.5-cardiac-like phenotype efficiently. Differentiated myotubes elicited faster Nav1.5 currents than those recorded from myoblasts. Unlike myoblasts, INa recorded in myotubes exhibited an accumulation of inactivation after the application of trains of pulses, due to a slower recovery from inactivation. Since Navβ subunits modulate channel gating and pharmacology, the goal of the present work was to study Navβ subunits during myogenesis. All four Navβ (Navβ1–4) isoforms were present in L6E9 myocytes. While Navβ1–3 subunits were up-regulated by myogenesis, Navβ4 subunits were not. These results show that Navβ genes are strongly regulated during muscle differentiation and further support a physiological role for voltage-gated Na+ channels during development and myotube formation. [Copyright &y& Elsevier]

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: Celecoxib is a COX-2 inhibitor that has been related to an increased cardiovascular risk and that exerts several actions on different targets. The aim of this study was to analyze the effects of this drug on human cardiac voltage-gated potassium channels (Kv) involved on cardiac repolarization Kv1.5 (I Kur ), Kv4.3+KChIP2 (I to1) and Kv7.1+KCNE1 (I Ks ) and to compare with another COX-2 inhibitor, rofecoxib. Currents were recorded in transfected mammalian cells by whole-cell patch-clamp. Celecoxib blocked all the Kv channels analyzed and rofecoxib was always less potent, except on Kv4.3+KChIP2 channels. Kv1.5 block increased in the voltage range of channel activation, decreasing at potentials positive to 0mV. The drug modified the activation curve of the channels that became biphasic. Block was frequency-dependent, increasing at fastest frequencies. Celecoxib effects were not altered by TEAout in R487Y mutant Kv1.5 channels but the kinetics of block were slower and the degree of block was smaller with TEAin, indicating that celecoxib acts from the cytosolic side. We confirmed the blocking properties of celecoxib on native Kv currents from rat vascular cells, where Kv1.5 are the main contributors (IC 50 ≈7μM). Finally, we demonstrate that celecoxib prolongs the action potential duration in mouse cardiac myocytes and shortens it in guinea pig cardiac myocytes, suggesting that Kv block induced by celecoxib may be of clinical relevance. [Copyright &y& Elsevier]