The calcium receptor for Ca reversal is blocked by manganese in rat uterine smooth muscle.

The effects of Mn ion on Ca reversal, which is the name for the inhibitory action of a minute amount of Ca ion on contraction of rat uterine muscle in Ca-free medium (exo-Ca-free contraction), was tested. Mn ion inhibited Ca reversal by antagonizing the intracellular action of a minute amount of Ca ion in inhibiting exo-Ca-free contraction. As the concentration of Ca ion required for Ca reversal was very low and Mn ion antagonized its action, the action site of Ca ion for Ca reversal must be very specific and can be called "The Ca receptor for Ca reversal".