Increased sensitivity of serotonin on the voltage-dependent K+ channels in mesenteric arterial smooth muscle cells of OLETF rats

This study examined the mechanisms of hypertension in diabetes. We investigated the effects of serotonin (5-HT) on voltage-dependent K+ (Kv) channel activity, vasoconstriction, 5-HT receptor expression levels, and the involvement of protein kinase C (PKC) in mesenteric arteries of Otsuka Long-Evans Tokushima fatty (OLETF) rats compared with Long-Evans Tokushima Otsuka (LETO) rats. Blood pressure, body weight, blood glucose level, and mesenteric arterial wall thickness were greater in OLETF rats. The 5-HT-induced vasoconstriction of mesenteric arteries was greater in OLETF rats than in LETO rats and inhibited by the 5-HT2A inhibitor inhibitor, ketanserin. The Kv currents in mesenteric arterial smooth muscle cells (MASMCs), determined using a perforated patch clamp technique, was inhibited by 1 mM 4-AP (42.5 ± 4.1% vs. 63.5 ± 2.3% in LETO vs. OLETF rats at +40 mV), but was insensitive to 1 mM TEA and 100 nM iberiotoxin. The inhibition of Kv current by 1 μM 5-HT in MASMCs was greater in OLETF rats than in LETO rats (17.1 ± 2.2% vs. 33.2 ± 2.7% in LETO vs. OLETF rats at +40 mV), and the inhibition was prevented by treatment with the PKCα- and β- selective inhibitor, Gö6976. The expression level of 5-HT2A, but not 5-HT2B, receptor and the expression levels of total PKC, PKCβ, and PKCε, but not PKCα, were higher in the mesenteric arteries of OLETF rats compared with LETO rats. The enhanced expression of 5-HT2A receptor together with PKCβ may promote mesenteric vasoconstriction and increase vascular resistance in OLETF rats.