Intracellular calcium-dependent contractile effects of serotonin in the human umbilical artery

Absence of innervation is a hallmark of human umbilical vessels. Intervillous space blood flow is regulated by vasoactive substances and calcium dependent contractility, both in normal and pathological conditions such as preeclampsia-eclampsia. To obtain additional information on the intracellular calcium contractile effects of serotonin in human umbilical arteries. Umbilical arteries from normal pregnancies were dissected, cut in 5 mm rings and mounted in a temperature-controlled isolated organ chamber, using calcium-free Krebs solution. The contractile effects of serotonin, lantane, verapamil and cyclopiazonic acid were evaluated at different concentrations using a computer coupled biopac polygraph. No differences in response were observed in the presence and absence of intracellular calcium. The positive contractile effects observed with serotonin were significantly decreased with repeated stimulation. An increase in the basal tone of the vessel was observed after calcium supplementation was added to the solution. This effect was minimized in the presence of verapamil and lantane. The contractile effects of serotonin in the calcium-free solution were not affected by the presence of cyclopiazonic acid. Serotonin contractile effects in the human umbilical artery depend mainly on intracellular calcium levels which favor the gradual entrance of this ion over time. Calcium influx induced by serotonin is possible through L and Non-L channels apparently insensitive to ciclopiozonic acid.