The Effects of Extracellular Magnesium on Gastrointestinal Contractility

Abstract

BACKGROUND/AIMS: Magnesium (Mg2+) is the second most abundant anion in the human body. It plays important roles including as a cofactor in many critical enzyme systems like energy transfer, storage and utilization. Changes in the concentration of extracellular Mg2+ may cause many pathological conditions such as neuromuscular hyperactivity, psychiatric disturbances, calcium/potassium abnormalities, and overactivity of cardiac muscle. Many investigations have been conducted on the effects of Mg2+ on cardiac, skeletal and vascular muscle contraction; however, much less is known about the effect of extracellular Mg2+ on gastrointestinal smooth muscle systems and gastrointestinal contractility. In the current study, we aimed to study the effects of extracellular Mg2+ on the isolated ileal responses induced by angiotensin II(ANG) contraction and in response to calcium and sodium channel blockers. MATERIALS and METHODS: Healthy adult Wistar rats were used in this work. The ileal segments were isolated and suspended in isolated organ tissue-bath. The contractile responses induced with ANG were recorded. To study the effects of extracellular magnesium, the perfusion medium was changed to without magnesium, 2xMg and 4xMg. In these standard and modified perfusion mediums, the ileal segments were incubated with the calcium channel blocker diltiazem (Benz(othi)azepines) and sodium channel blocker prilocaine (2-(Propylamino)-o-propionotoluidide) and then ANG-induced contraction was recorded. RESULTS: The results showed that in the Mg-free perfusion medium the ANG-induced contractions were increased and when extracellular magnesium was increased 2x-fold and 4x-fold in the perfusion medium, the ANG-induced responses were significantly decreased. Also, in the standard and modified Mg perfusion medium, the calcium and sodium channel blockers significantly decreased the ANG-induced contractions in isolated ileal segments. CONCLUSION: Changes in the extracellular magnesium concentration in the perfusion medium significantly affect the gastrointestinal contractility. Without Mg, the contractility was increased, but with 2x-fold and 4x-fold increases in Mg, the contractility was significantly decreased. Mg had a dose-dependent inhibitory effect on ANG-induced contractions in the isolated ileal segments.