Effects of Magnesium on Human Umbilical Arteries: Role of Intracellular Calcium Stores

Abstract

The purpose of this investigation on human umbilical arteries was: (1) to analyze the effects of magnesium (Mg²⁺) in the prevention of contractions induced by 5-hydroxytryptamine (5-HT), KCl, Bay K 8644 and BaCl₂; (2) to determine whether the presence of Mg²⁺ could modulate the response to caffeine in Ca²⁺-free medium at 25 and 37°C, and (3) to examine the influence of Mg²⁺ and temperature in the release of intracellular calcium induced by 5-HT in Ca²⁺-free medium. Human umbilical arteries were dissected and mounted in organ baths for isometric measurement of force. Our results showed: (1) Mg²⁺ is a potent inhibitor of smooth muscle contraction of human umbilical arteries caused by 5-HT, KCl, Bay K 8644 and BaCl₂, and that this effect might be due to the inhibition of the transmembrane calcium influx. (2) The relaxant effect of Mg²⁺ did not seem to be mediated by a blockade of the release of calcium from an intracellular store. (3) Moreover, our results suggest an effect of temperature independent from the action of Mg²⁺ on 5-HT-induced contraction.

Methodological challenges in using human umbilical artery as a model for in vitro studies

“…Experimental protocols performed in Ca 2+ ‐free Krebs‐bicarbonate solution are interesting, providing insight into the role of extracellular and/or intracellular Ca 2+ in the contractile activity of the tested compound. In this protocol, we showed that nicardipine not only suppresses serotonin contraction, but also significantly suppresses BaCl 2 ‐induced contraction and completely blocks the contraction induced by the L‐type Ca 2+ channel agonist BAY K 8644, indicating that the contractile mechanisms in HUAs are similar to those in other vascular smooth muscle cells (Tiritilli, 1998 ).…”