We studied the involvement of different types of Ca2+ channels, cyclic nucleotides and different kinases in the regulation of human umbilical artery (HUA) contractility. The elucidation of the precise mechanisms regulating the contractility of this artery could be very important to reveal potential therapeutic targets to treat HUA disorders such as preeclampsia. The relevancy of different types of Ca2+ channels on the regulation of HUA tonus was analyzed. Among the different Ca2+ channel inhibitors used, only the L-type calcium channels (LTCC) inhibition induced relaxation of HUA in Ca2+ containing medium. The inhibition of T-type calcium channels (TTCC) or TRP channels did not significantly affect HUA contractility. In presence of Ca2+, the intracellular increase of a cyclic nucleotide (cAMP or cGMP) induces relaxation of HUA, which was almost complete in histamine-con- tracted HUA, and lower effect was observed in arteries contracted by KCl and serotonin (5-HT). Inhibition of PKA and PKG weakly reduced the relaxations induced by the increase of cAMP and cGMP respectively, suggesting that the relaxation induced by these nucleotides is not totally mediated by the activation of their respective kinases and that other mechanisms are involved. In calcium containing solution, PP2A inhibition produces relaxation of contracted HUA. In KCl contracted arteries, the OA and nifedipine relaxant effects are similar and not additive, suggesting that PP2A could activate LTCC. Besides, the increase of cyclic nucleotides significantly increased the OA effect, suggesting that the effect of PP2A inhibition is independent of the cyclic nucleotide pathways. The contractions induced by KCl, histamine and 5-HT in presence of Ca2+ were not significantly affected by ROCK, ERK1/2 or p38MAPK inhibitors. In absence of extracellular Ca2+, histamine and 5-HT elicited contractions of HUA characterized by two components, a rapid phasic contractile component followed by a decrease of the contraction until a tonic component. However, KCl elicited sustained contractions of HUA in absence of extracellular Ca2+. As in presence of calcium, the ERK1/2 and p38MAPK inhibitors did not influence the contractions induced by KCl, histamine or 5-HT in absence of extracellular Ca2+. However, in these conditions, ROCK inhibition significantly relaxed the contractions induced by KCl and reduced the phasic and tonic components of the contraction elicited either by histamine or 5-HT. Our results show that calcium-dependent contractions of HUA depend on Ca2+ entry by LTCC, and these chan- nels seems to be positive regulated by PP2A. Cyclic nucleotides mediate HUA vasodilatation but their dependent kinases are not the unique responsible of this effect. HUA is able to contract independently of Ca2+ influx by activating the ROCK pathway and/or due to intracellular Ca2+ release.
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