Impaired Ca2+ handling in resistance arteries from genetically obese Zucker rats: Role of the PI3K, ERK1/2 and PKC signaling pathways.

The impact of obesity on vascular smooth muscle (VSM) Ca2+ handling and vasoconstriction, and its regulation by the phosphatidylinositol 3-kinase (PI3K), mitogen activated protein kinase (MAPK) and protein kinase C (PKC) were assessed in mesenteric arteries (MA) from obese Zucker rats (OZR). Simultaneous measurements of intracellular Ca2+ ([Ca2+]i) and tension were performed in MA from OZR and compared to lean Zucker rats (LZR), and the effects of selective inhibitors of PI3K, ERK-MAPK kinase and PKC were assessed on the functional responses of VSM voltage-dependent L-type Ca2+ channels (CaV1.2). Increases in [Ca2+]i induced by α1-adrenoceptor activation and high K+ depolarization were not different in arteries from LZR and OZR although vasoconstriction was enhanced in OZR. Blockade of the ryanodine receptor (RyR) and of Ca2+ release from the sarcoplasmic reticulum (SR) markedly reduced depolarization-induced Ca2+ responses in arteries from lean but not obese rats, suggesting impaired Ca2+-induced Ca2+ release (CICR) from SR in arteries from OZR. Enhanced Ca2+ influx after treatment with ryanodine was abolished by nifedipine and coupled to up-regulation of CaV1.2 channels in arteries from OZR. Increased activation of ERK-MAPK and up-regulation of PI3Kδ, PKCβ and δ isoforms were associated to larger inhibitory effects of PI3K, MAPK and PKC blockers on VSM L-type channel Ca2+ entry in OZR. Changes in arterial Ca2+ handling in obesity involve SR Ca2+ store dysfunction and enhanced VSM Ca2+ entry through L-type channels, linked to a compensatory up-regulation of CaV1.2 proteins and increased activity of the ERK-MAPK, PI3Kδ and PKCβ and δ, signaling pathways.