Na(+)-independent glucose utilization during Mn(2+)-induced contraction in ileal longitudinal smooth muscle

In Ca(2+)- and Na(+)-deficient, isotonic 126 mM K+ medium, addition of 5 mM Mn2+ caused a tension about 2.5 x greater than the tonic response induced by 126 mM K+ medium (Ca2+ 2.5 mM, Na+ 0 mM) in ileal muscle. When glycogen was depleted by incubation in a glucose-free, hypertonic 60 mM K+ medium, addition of 5 mM Mn2+ induced only a very weak tension in Ca(2+)-free, isotonic 126 K+ medium. Phlorizin (10(-3) M), a blocker of Na(+)-coupled glucose cotransporter and ouabain (9 x 10(-5) M), an inhibitor of Na+, K(+)-ATPase, failed to inhibit the tension elicited by 5 mM Mn2+ in a Ca(2+)- and Na(+)-deficient, isotonic 126 mM K+ medium. Mn2+ was accumulated in the intracellular compartment in a Ca(2+)- and Na(+)-deficient, isotonic 126 mM K+ medium. The tissue ATP concentration was significantly reduced in a Na(+)-deficient 126 mM K+ medium. However, it recovered almost completely when 5 mM Mn2+ was added to the isotonic 126 mM K+ medium. These results suggest that the Mn(2+)-induced contraction in depolarized ileal longitudinal muscle in Na(+)-deficient medium may be maintained by a glucose transport which is not dependent on Na+ and insensitive to phlorizin.