Action of ouabain on the contraction of ileal longitudinal muscle by manganese ions in a Ca2+-free, high-K+, Na+-sufficient or Na+-deficient solution

Abstract

The action of ouabain, an external Na+-dependent inhibitor of active glucose transport, on the contraction by Mn2+in a Ca2+-free, Na+-sufficient or Na+-deficient medium was examined in ileal muscle. Ouabain ( 9 × 10−5m) inhibited the contraction by 5 mm Mn2+in a Ca2+-free, 60 mm K+, Na+-sufficient medium in ileal muscle. The addition of pyruvate or lactate, utilized independently in the external Na+in the pretreatment with ouabain, induced the dose-dependent contraction and manganese uptake by Mn2+in the Ca2+-free, 60 mm K+, Na+-sufficient medium. These results suggest that Mn2+-induced ileal contraction in a high-K+, Na+-sufficient medium is maintained by an active glucose transport, dependent on external Na+. While, in contrast, Mn2+-induced contraction in a high-K+, Na+-deficient medium is maintained by an external Na+-independent glucose transport, and is insensitive to ouabain.