Ischemia induces partial loss of surface membrane polarity and accumulation of putative calcium ionophores

Bruce Molitoris, P. D. Wilson, R. W. Schrier, F. R. Simon

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Abstract

To determine if ischemia induces alterations in renal proximal tubule surface membranes, brush border (BBM) and basolateral membranes (BLM) were isolated simultaneously from the same cortical homogenate after 50 min of renal pedicle clamping. Ischemia caused a selective decrease in the specific activity of BBM marker enzymes leucine aminopeptidase and alkaline phosphatase, but did not effect enrichment (15 times). Neither specific activity nor enrichment (10 times) of BLM NaK-ATPase was altered by ischemia. Contamination of BBM by intracellular organelles was also unchanged, but there was an increase in the specific activity (41.1 vs. 60.0, P <0.01) and enrichment (2.3 vs. 4.3, P <0.01) of NaK-ATPase in the ischemic BBM fraction. Ischemia increased BLM lysophosphatidylcholine (1.3 vs. 2.5%, P <0.05) and phosphatidic acid (0.4 vs. 1.3%, P <0.05). Ischemia also decreased BBM sphingomyelin (38.5 vs. 29.6%, P <0.01) and phosphatidylserine (16.1 vs. 11.4%, P <0.01), and increased phosphatidylcholine (17.2 vs. 29.7%, P <0.01), phosphatidylinositol (1.8 vs. 4.6%, P <0.01), and lysophosphatidylcholine (1.0 vs. 1.8%, P <0.05). The large changes in BBM phospholipids did not result from new phospholipid synthesis, since the specific activity (32P dpm/nmol Pi) of prelabeled individual and total phospholipids was unaltered by ischemia. We next evaluated if these changes were due to inability of ischemic cells to maintain surface membrane polarity. Cytochemical evaluation showed that while NaK-ATPase could be detected only in control BLM, specific deposits of reaction product were present in the BBM of ischemic kidneys. Furthermore, using continuous sucrose gradients, the enzymatic profile of ischemic BBM NaK-ATPase shifted away from ischemic BLM NaK-ATPase and toward the BBM enzymatic marker leucine aminopeptidase. Taken together, these data suggest that NaK-ATPase activity determined enzymatically and cytochemically was located within ischemic BBM. We propose that ischemia impairs the ability of cells to maintain surface membrane polarity, and also results in the accumulation of putative calcium ionophores.

Original languageEnglish (US)
Pages (from-to)2097-2105
Number of pages9
JournalJournal of Clinical Investigation
Volume76
Issue number6
StatePublished - 1985
Externally publishedYes

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Calcium Ionophores
Ischemia
Adenosine Triphosphatases
Membranes
Leucyl Aminopeptidase
Phospholipids
Lysophosphatidylcholines
Kidney
Proximal Kidney Tubule
Phosphatidic Acids
Sphingomyelins
Phosphatidylserines
Microvilli
Phosphatidylinositols
Phosphatidylcholines
Constriction
Organelles
Alkaline Phosphatase
Sucrose
Enzymes

ASJC Scopus subject areas

  • Medicine(all)

Cite this

Ischemia induces partial loss of surface membrane polarity and accumulation of putative calcium ionophores. / Molitoris, Bruce; Wilson, P. D.; Schrier, R. W.; Simon, F. R.

In: Journal of Clinical Investigation, Vol. 76, No. 6, 1985, p. 2097-2105.

Research output: Contribution to journalArticle

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abstract = "To determine if ischemia induces alterations in renal proximal tubule surface membranes, brush border (BBM) and basolateral membranes (BLM) were isolated simultaneously from the same cortical homogenate after 50 min of renal pedicle clamping. Ischemia caused a selective decrease in the specific activity of BBM marker enzymes leucine aminopeptidase and alkaline phosphatase, but did not effect enrichment (15 times). Neither specific activity nor enrichment (10 times) of BLM NaK-ATPase was altered by ischemia. Contamination of BBM by intracellular organelles was also unchanged, but there was an increase in the specific activity (41.1 vs. 60.0, P <0.01) and enrichment (2.3 vs. 4.3, P <0.01) of NaK-ATPase in the ischemic BBM fraction. Ischemia increased BLM lysophosphatidylcholine (1.3 vs. 2.5{\%}, P <0.05) and phosphatidic acid (0.4 vs. 1.3{\%}, P <0.05). Ischemia also decreased BBM sphingomyelin (38.5 vs. 29.6{\%}, P <0.01) and phosphatidylserine (16.1 vs. 11.4{\%}, P <0.01), and increased phosphatidylcholine (17.2 vs. 29.7{\%}, P <0.01), phosphatidylinositol (1.8 vs. 4.6{\%}, P <0.01), and lysophosphatidylcholine (1.0 vs. 1.8{\%}, P <0.05). The large changes in BBM phospholipids did not result from new phospholipid synthesis, since the specific activity (32P dpm/nmol Pi) of prelabeled individual and total phospholipids was unaltered by ischemia. We next evaluated if these changes were due to inability of ischemic cells to maintain surface membrane polarity. Cytochemical evaluation showed that while NaK-ATPase could be detected only in control BLM, specific deposits of reaction product were present in the BBM of ischemic kidneys. Furthermore, using continuous sucrose gradients, the enzymatic profile of ischemic BBM NaK-ATPase shifted away from ischemic BLM NaK-ATPase and toward the BBM enzymatic marker leucine aminopeptidase. Taken together, these data suggest that NaK-ATPase activity determined enzymatically and cytochemically was located within ischemic BBM. We propose that ischemia impairs the ability of cells to maintain surface membrane polarity, and also results in the accumulation of putative calcium ionophores.",
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AU - Schrier, R. W.

AU - Simon, F. R.

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