Contractile effects of manganese on taenia of guinea pig cecum.

The present study was undertaken to examine Mn as a contractile agent in its own right in the absence of extracellular Ca and after the depletion of Ca from agonist-releasable stores. The results show that isolated strips of taenia coli depolarized by high-K, Ca-free solution will contract when Mn is present. Similarly, carbachol will evoke contractions in tissues incubated in Ca-free, Mn-containing solutions. In addition, it seems possible to stimulate contraction by releasing Mn from an agonist-releasable intracellular store in the absence of extracellular Ca and Mn. Therefore the possibility exists that cations employed as Ca antagonists may in fact support contraction.