Characterization of a Mg-dependent, Na-inositol co-transport process in cardiac sarcolemmal vesicles.
[3H]-myo-Inositol transport into cardiac sarcolemmal vesicles is both a time- and Na(+)-dependent process. Transport was stimulated 3-fold by 1 microM valinomycin suggesting the process is electrogenic. myo-Inositol transport was dependent upon the presence of Mn2+ or Mg2+ but not Ca2+. Kinetic analysis revealed a high affinity transport process that was saturable (Vmax, 650 +/- 71 pmoles myo-inositol/mg protein/min; Km, 37.7 +/- 1.3 microM) and a low affinity process that was unsaturable up to 1.0 mM substrate. Transport was not inhibited by 1.0 mM of either L-glucose, D- or L-galactose. However, D-glucose and L-fucose at 1.0 mM were inhibitory. Higher concentrations (30 mM) of each of the sugars inhibited transport. myo-Inositol transport was also inhibited by the inositol isomers (1.0 mM), D-chiro-inositol, epi-inositol and scyllo-inositol with scyllo-inositol being most effective. Kinetic analysis established scyllo-inositol as a competitive inhibitor of cardiac myo-inositol transport, increasing the Km for substrate three-fold (122 +/- 21 microM). These data indicate that inositol transport across cardiac sarcolemma is a Mg(2+)-dependent Na+ co-transport process that is electrogenic and stereospecific.
Rubin
L J
LJ
John M. Dalton Research Center, University of Missouri-Columbia 65211.
Hale
C C
CC
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005643:Fucose / Q000494:pharmacology; D005690:Galactose / Q000494:pharmacology; D008401:Gas Chromatography-Mass Spectrometry; D005947:Glucose / Q000494:pharmacology; D006352:Heart Ventricles / Q000648:ultrastructure; D007294:Inositol / Q000378:metabolism / Q000493:pharmacokinetics*; D007536:Isomerism; D008274:Magnesium / Q000494:pharmacology*; D010743:Phospholipids / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D012964:Sodium / Q000378:metabolism / Q000493:pharmacokinetics*; D013997:Time Factors; D014316:Tritium; D014634:Valinomycin / Q000494:pharmacology
D010743:Phospholipids; D014316:Tritium; D014634:Valinomycin; D005643:Fucose; D007294:Inositol; D012964:Sodium; D008274:Magnesium; D005947:Glucose; D005690:Galactose