Characterisation of mechanisms of relaxation induced by omega‐3 polyunsaturated fatty acids (n‐3 PUFA) EPA and DHA in rat aorta and mesenteric arteries: A novel a role for IK Ca and TRPV4 channels in DHA mediated relaxation

The omega‐3 polyunsaturated fatty acids (n‐3 PUFA) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) known as “fish oils” are associated with improved cardiovascular health. Their ability to relax blood vessels and reduce blood pressure contribute to these effects. Numerous studies investige the mechanisms of n‐3 PUFA mediated relaxation and various vasodilator mechanisms are implicated, including the NOS and COX pathways, and a direct effect on BK Ca channels. Few studies fully characterised the dilator response and focus on either DHA or EPA in a single artery. We conducted a full characterisation of the various potential vasodilator mechanisms for both fish oils in a large muscular artery (aorta) and a resistance artery (mesenteric). Male Wistar rats (250–300g) were killed by overdose of inhaled isoflurane, thoracic aorta and mesenteric arteries were dissected and cut in to 2mm rings and mounted in a wire myograph (DMT 620) in Krebs solution. Arteries were pre‐constricted with the thromboxane mimetic U46619 (10–500 nM) and concentration response curves were constructed for DHA or EPA (100 nM‐30 μM) mediated relaxation. Block of mechanisms involved in vasodilation namely NOS (L‐NAME; 300μM), COX (indometacin; 10 μM) SKCa (apamin; 50 nM), IKCa (TRAM‐34; 1μM), BKCa (Paxilline; 1μM) and TRPV4 (RN‐1734; 30μM) were assessed on relaxations to DHA and EPA. HEK cells expressing TRPV4, and loaded with FLUO4‐AM calcium increases induced by activation of TRPV4 andn‐3 PUFA we measured. Data are expressed as mean±SEM (% relaxation or fraction of ionomycin response). P<0.05 was considered statistically significant (one‐way ANOVA with Bonferroni's or Tukeys' Post‐test). In mesenteric arteries, relaxations to EPA but not DHA were slightly inhibited by L‐NAME, in aorta only DHA relaxation was partially inhibited (Figure 1). Inhibition of COX had no inhibitory effect on DHA or EPA mediated relaxation (Figure 1). In aorta inhibition of IK Ca , SK Ca and TRPV4 channels had no effect on relaxations to DHA or EPA (Figure 2). Inhibition of BK Ca caused significant block of DHA mediated relaxation only. In mesenteric arteries, DHA mediated relaxation was inhibited by blockade of BK Ca , IK Ca and TRPV4 (Figure 3). In HEK cells expressing TRPV4 neither fish oil potentiated or evoked a TRPV4 mediated increase in calcium (Figure 4) Our Results indicate diverse mechanisms contribute to n‐3 PUFA mediated relaxation; depending on the artery studied and the n‐3 PUFA. Involvement of the NOS and COX pathways was minimal. BK Ca channels are proposed underlie vasodilator and blood pressure lowering effects of n‐3 PUFA and our data partially support this: DHA mediated relaxation was reduced by inhibition of BK Ca . However, BK Ca has no role in EPA mediated relaxation. In mesenteric arteries, DHA‐mediated relaxation involves IK Ca and TRPV4 channels but noin the aorta or EPA‐mediated relaxation in either artery. n‐3 PUFA do not activate TRPV4 so they do not underlie DHA mediated activation of IK Ca . There is a large component of relaxation residual to all combinations of blocking drugs indicating other mechanisms critical in n‐3 PUFA mediated relaxations remain to be elucidated. We present in an accompanying poster that these mechanisms involve potassium channels. Support or Funding Information This work was supported by the British Heart Foundation PG/11/93/21943