Effect of calcium and ROCK in the regulation of human umbilical artery contractility

Joana Feiteiro, Eduarda Lemos, Ignacio Verde, Elisa Cairrao. University of Beira Interior, CICS-UBI, Health Sciences Research Centre, 6200-506 Covilhã, Portugal., Portugal

In general, vascular smooth muscle contractions depend on a Ca2+ intracellular increase. Previous studies performed by our group with human umbilical artery (HUA) suggested that the contractions induced by different agents vary inversely with the extracellular calcium concentration. Consequently, at 1.5mM of extracellular only 45% of HUA rings induced a maximal contraction up to 1000 mg when challenged with serotonin (5-HT). However, at 0.5mM of extracellular calcium this percentage increases until 80%. To better know this process, we studied the effects of different concentrations of calcium in the regulation of HUA contractility.

Using standard organ bath techniques as previously described Cairrao et al. (2008), rings of HUA without endothelium were contracted by 5-HT (1 μM), histamine (10 μM) and the effect of different concentrations of calcium was analysed. The concentration-response curves to Ca2+ were different dependent of the calcium concentration of the bath solution.

The results showed that at low concentrations of calcium (0.2mM Ca2+) the contractions induced by 5-HT and histamine were 2915.4 ± 239.9 e 1301.1±365.7 respectively. Inversely, at high concentrations of calcium (1mM, 2mM and 3mM) the maximal contractions caused by 5-HT and histamine were lower. Afterwards, we analysed the role of Rho-kinase (ROCK) in this process, and different types of experiments were performed. When HUA were preconditioned with 0.5 and 3.0 mM Ca2+ the inhibitor of ROCK, Y-27632 were purchased from Tocris (Madrid, Spain), induced relaxation only in the 3.0 mM Ca2+ preconditioned HUA. Also, our results suggested that the presence of Y-27632 (10μM) modifies the concentration-response curves to Ca2+ induced in presence of 5-HT or histamine.

In summary, our results demonstrate that HUA contractility is very sensitive to extracellular calcium levels and this can constitute a dynamic mechanism to regulate the contractility of this artery. ROCK seems to play a key role in the regulation and activation of different contractile pathways depending on the extracellular Ca2+ concentration.

Cairrao, E., Alvarez, E., Santos-Silva, A.J., Verde, I., 2008. Potassium channels are involved in testosterone-induced vasorelaxation of human umbilical artery. Naunyn. Schmiedebergs Arch. Pharmacol. 376, 375-383.