Segmental heterogeneity in the biochemical properties of the Na+-K+-ATPase along the intestine of the gilthead seabream (Sparus aurata L.).
The activity of the Na+-K+-ATPase along the intestinal mucosa of the gilthead seabream has been examined. Under optimal assay conditions, found at 35 degrees C, pH 7.5, 2-5 mM MgCl2, 5 mM ATP, 10 mM K+ and 200 mM Na+, maximal Na+-K+-ATPase activities were found in the microsomal fraction of pyloric caeca (PC) and anterior intestine (AI), which were more than two-fold the activity measured in the microsomes from the posterior intestine (PI). Na+-K+-ATPase activities from PC, AI and PI displayed similar pH dependence, optimal Mg2+/ATP and Na+/K+ ratios, affinities for Mg2+ and ATP, and inhibition by vanadate. However, considerable differences regarding sensitivity to ouabain, inhibition by calcium and responses to ionic strength were observed between segments. Thus, Na+-K+-ATPase activity from the AI was found to be ten-fold more sensitive to ouabain and calcium than the enzyme from the PC and PI and displayed distinct kinetic behaviours with respect to Na+ and K+, compared to PC and PI. Analysis of the data from the AI revealed the presence of two Na+-K+-ATPase activities endowed with distinguishable biochemical characteristics, suggesting the involvement of two different isozymes. Regional differences in Na+-K+-ATPase activities in the intestine of the gilthead seabream are compared with literature data on Na+-K+-ATPase isozymes and discussed on the basis of the physiological differences between intestinal regions.
Almansa
E
E
Departamento de Biología Animal, Facultad de Biología, Universidad de La Laguna, Tenerife, Canary Islands, Spain.
Sanchez
J J
JJ
Cozzi
S
S
Casariego
M
M
Cejas
J
J
Díaz
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007422:Intestines / Q000201:enzymology*; D008274:Magnesium / Q000378:metabolism; D009928:Organ Specificity; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000493:pharmacokinetics; D021541:Sea Bream / Q000378:metabolism*; D012964:Sodium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*
D004791:Enzyme Inhibitors; D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium