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Dietary polyunsaturated fatty acids (PUFAs) have been reported to exhibit antiarrhythmic properties, which have been attributed to their availability to modulate [Na.sup.+], Ca[2.sup.+], and several [K.sup.+] channels. However, their effects on human ether-a-go-go-related gene (HERG) channels are unknown. In this study we have analyzed the effects of arachidonic acid (AA, [omega]-6) and docosahexaenoic acid (DHA, [omega]-3) on HERG channels stably expressed in Chinese hamster ovary cells by using the whole cell patch-clamp technique. At 10 [micro]M, AA and DHA blocked HERG channels, at the end of 5-s pulses to -10 mV, to a similar extent (37.7 [+ or -] 2.4% vs. 50.2 [+ or -] 8.1%, n = 7-10, P > 0.05). 5,6,11,14-Eicosatetrayenoic acid, a nonmetabolizable AA analog, induced effects similar to those of AA on HERG current. Both PUFAs shifted the midpoint of activation curves of HERG channels by -5.1 [+ or -] 1.8 mV (n = 10, P < 0.05) and -11.2 [+ or -] 1.1 mV (n = 7, P < 0.01). Also, AA and DHA shifted the midpoint of inactivation curves by +12.0 [+ or -] 3.9 mV (n = 4; P < 0.05) and +15.8 [+ or -] 4.3 mV (n = 4; P < 0.05), respectively. DHA and AA accelerated the deactivation kinetics and slowed the inactivation kinetics at potentials positive to +40 mV. Block induced by DHA, but not that produced by AA, was higher when measured after applying a pulse to -120 mV (I [right arrow] O). Finally, both AA and DHA induced a use-dependent inhibition of HERG channels. In summary, block induced by AA and DHA was time, voltage, and use dependent. The results obtained suggest that both PUFAs bind preferentially to the open state of the channel, although an interaction with inactivated HERG channels cannot be ruled out for AA. [K.sup.+] channel; membrane currents; ion channels; arrhythmia; antiarrhythmics

Aims Polyunsaturated fatty n-3 acids (PUFAs) have been reported to exhibit antiarrhythmic properties. However, the mechanisms of action remain unclear. We studied the electrophysiological effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on IKs, and on the expression and location of Kv7.1 and KCNE1. Methods and results Experiments were performed using patch-clamp, western blot, and sucrose gradient techniques in COS7 cells transfected with Kv7.1/KCNE1 channels. Acute perfusion with both PUFAs increased Kv7.1/KCNE1 current, this effect being greater for DHA than for EPA. Similar results were found in guinea pig cardiomyocytes. Acute perfusion of either PUFA slowed the activation kinetics and EPA shifted the activation curve to the left. Conversely, chronic EPA did not modify Kv7.1/KCNE1 current magnitude and shifted the activation curve to the right. Chronic PUFAs decreased the expression of Kv7.1, but not of KCNE1, and induced spatial redistribution of Kv7.1 over the cell membrane. Cholesterol depletion with methyl-β-cyclodextrin increased Kv7.1/KCNE1 current magnitude. Under these conditions, acute EPA produced similar effects than those induced in non-cholesterol-depleted cells. A ventricular action potential computational model suggested antiarrhythmic efficacy of acute PUFA application under IKr block. Conclusions We provide evidence that acute application of PUFAs increases Kv7.1/KCNE1 through a probably direct effect, and shows antiarrhythmic efficacy under IKr block. Conversely, chronic EPA application modifies the channel activity through a change in the Kv7.1/KCNE1 voltage-dependence, correlated with a redistribution of Kv7.1 over the cell membrane. This loss of function may be pro-arrhythmic. This shed light on the controversial effects of PUFAs regarding arrhythmias. [ABSTRACT FROM AUTHOR]

Objective: The Ca2+-independent transient outward K+ current (Ito) plays a crucial role in shaping the cardiac action potential. In the present study, we examined whether angiotensin II (AngII) regulated the Ito as well as the putative intracellular cascade responsible for the effects. Methods: Ito was recorded in rat ventricular myocytes using the nystatin-perforated patch-clamp configuration. Results: AngII (0.1 μM) inhibited Ito (21.9±4.8% at +40 mV), but not the IK1, in a voltage- and time-independent manner. The inhibition decreased at concentrations higher than 1 μM resulting in a bell-shaped dose–response curve (IC50=3.1±1.5 μM). The blocking effects were abolished in the presence of the type 2 AngII receptor (AT2R) antagonist PD123319, but not in the presence of the selective type 1 AngII receptor (AT1R) antagonist candesartan. Moreover, the selective AT2R agonist CGP42112A completely reproduced the effects of AngII (20.5±2.4% of block at +40 mV), indicating that AngII-induced Ito block was mediated via stimulation of AT2R. Furthermore, selective stimulation of AT2R by CGP42112A significantly prolonged the rat atrial action potentials recorded using conventional microelectrode techniques. The AngII-induced inhibition of Ito was not modified by either Nϖ-nitro-l-arginine-methyl ester (l-NAME) or eicosatetrayonic acid (ETYA), indicating that neither the nitric oxide (NO)–guanosine 3′,5′-cyclic monophosphate (cGMP) system nor the arachidonic acid cascade was implicated in the effects of AngII on Ito. However, the AngII-induced Ito inhibition was completely abolished by the serine/threonine phosphatase type 2A (PP2A) inhibitors, okadaic acid and cantharidin, but not by the inactive analog of okadaic acid, 1-norokadaone. Intracellular application of PP2A decreased Kv4.2 currents recorded in transiently transfected Chinese hamster ovary cells (CHO). Conclusion: These results indicate that AngII activates PP2A through the stimulation of the AT2R, resulting in a decrease of the Ito amplitude. [Copyright &y& Elsevier]