Basolateral membrane lipid dynamics alter Na-K ATPase activity in rabbit small intestine.
The role of basolateral membrane fluidity in regulating Na-K ATPase activity along the crypt-villus axis in rabbit distal small intestine was assessed. Basolateral membranes were prepared from isolated villus and crypt enterocytes at 24- to 28-fold enhancement. Villus basolateral membranes were significantly (p < 0.001) more fluid than crypt basolateral membranes as measured by 1,6-diphenyl-1,3,5-hexatriene. No difference was seen between the two groups as measured by either 2-(9-anthroyloxy)-stearic fatty acid or 16-(9-anthroyloxy)-palmitic acid. Fluidity alterations were accompanied by an increased phospholipid content in villus membranes, which resulted in a decreased cholesterol:phospholipid ratio and an increased lipid:protein molar ratio. Na-K ATPase activity was significantly (p < 0.01) greater in villus basolateral membranes than in crypt membranes, and demonstrated a greater sensitivity to ouabain inhibition. Ouabain inhibition curves calculated from villus data fit well (p < 0.001) with a two binding site model, with a high affinity (Ki 16 nM) and a low affinity (Ki 4.2 microM) ouabain binding site. In crypt basolateral membranes, only a low affinity site was apparent (Ki 3.0 microM). Fluidizing crypt basolateral membranes in vitro with benzyl alcohol to levels seen in villus basolateral membranes resulted in the appearance of a high affinity ouabain binding site (Ki 110 nM) and an increased sensitivity of Na-K ATPase to ouabain inhibition. The fluidization of villus basolateral membranes eliminated the binding associated with the high affinity site. Treatment with methanol, as a control, did not alter Na-K ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Madsen
K L
KL
Department of Medicine, University of Alberta, Edmonton, Canada.
Meddings
J B
JB
Fedorak
R N
RN
D000818:Animals; D002784:Cholesterol / Q000032:analysis; D005454:Fluorescence Polarization; D007413:Intestinal Mucosa / Q000737:chemistry / Q000201:enzymology* / Q000502:physiology; D007421:Intestine, Small / Q000737:chemistry / Q000201:enzymology* / Q000502:physiology; D008560:Membrane Fluidity / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D010743:Phospholipids / Q000032:analysis; D011817:Rabbits; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*
D010743:Phospholipids; D010042:Ouabain; D002784:Cholesterol; D000254:Sodium-Potassium-Exchanging ATPase