Hepatocellular 22Na+ uptake: effect of oleate.
Whether cellular oleate uptake is Na+ coupled remains controversial. Our present studies document that hepatocellular [3H]oleate uptake is unaltered by isomotic substitution of Na+ with K+, Li+, or sucrose in Hanks' HEPES buffer. In parallel studies 22Na+ uptake was significantly (P less than 0.02) increased by concentrations of alanine that yielded [3H]-alanine uptakes greater than 24% of basal 22Na+ uptake when both were expressed as nanomoles per minute per 10(6) hepatocytes. Although [3H]glutamine uptake exceeded this threshold, maximal specific [3H]taurocholate uptake did not. Consistent with the observations with alanine, addition of glutamine, but not taurocholate, to the incubations resulted in a significant increase in 22Na+ uptake. The ionophore monensin increased uptake of 22Na+ under all conditions. Both in the absence and in the presence of HCO3- (4 and 25 mM), specific [3H]oleate uptake was sufficient to elicit a readily detectable effect on 22Na+ uptake, if Na+ and oleate were cotransported. However, addition of 1 mM oleate did not affect 22Na+ uptake in the absence of HCO3- (5.4 +/- 0.6 vs. control 5.4 +/- 0.4 nmol.min-1.10(6) cells-1) as well as in the presence of 4mM HCO3- (10.4 +/- 1.8 vs. control 9.9 +/- 1.1) and 25 mM HCO3- (10 +/- 1.3 vs. control 10.8 +/- 0.5). These data indicate that the predominant component of hepatocellular oleate uptake is not directly associated with Na+ influx. They do not exclude, however, a more complex or indirect link.
Sorrentino
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Department of Medicine (Division of Liver Diseases), Mount Sinai School of Medicine, City University of New York, New York 10029.
Van Ness
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K
Moukabary
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K
Berk
P D
PD
D000409:Alanine / Q000378:metabolism; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D066298:In Vitro Techniques; D008094:Lithium / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D017693:Sodium Bicarbonate; D012979:Sodium Radioisotopes; D013656:Taurocholic Acid / Q000378:metabolism
D001639:Bicarbonates; D009829:Oleic Acids; D012979:Sodium Radioisotopes; D005973:Glutamine; D019301:Oleic Acid; D013656:Taurocholic Acid; D017693:Sodium Bicarbonate; D008094:Lithium; D012964:Sodium; D000409:Alanine; D011188:Potassium