Actions of manganese ions in contraction of smooth muscle

1. Manganese ions (Mn2+) have been used in the last few decades as one of a number of inorganic Ca2+ channel blockers to investigate Ca2+ channels in excitable smooth muscle cells. 2. It has been recently reported that in addition to its inhibitory effects on the Ca2+ channels, Mn2+ in millimolar concentrations also produces contraction in the state of cell membrane depolarization. 3. Mn2+ has been shown to be able to permeate the cells via voltage-operated L-type Ca2+ channels in the membranes and directly activates contractile proteins in smooth muscles. 4. Intracellular sites of action have been proposed for Mn2+ in smooth muscles.