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.
Nasu
T
T
Department of Veterinary Pharmacology, Faculty of Agriculture, Yamaguchi University, Japan. nasu@agr.yamaguchi-u.ac.jp
Shibata
A
A
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects* / Q000378:metabolism; D007537:Isometric Contraction / Q000187:drug effects; D007552:Isotonic Solutions; D008297:Male; D008345:Manganese / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012462:Saline Solution, Hypertonic; D012964:Sodium / Q000494:pharmacology
D007552:Isotonic Solutions; D012462:Saline Solution, Hypertonic; D008345:Manganese; D000255:Adenosine Triphosphate; D012964:Sodium; D005947:Glucose; D011188:Potassium; D002118:Calcium