Hyperosmolality stimulates phospholipase A2 activity in rabbit renal medulla and in Madin-Darby canine kidney (MDCK) cells.

Renal medullary cells are able to accumulate glycerophosphocholine during adaptation to the high extracellular osmolality. The aim of this study was to investigate the effect of hyperosmolality on both phospholipase A2 activity and the rate of choline incorporation into glycerophosphocholine in rabbit renal medulla and Madin-Darby Canine Kidney cells. Phospholipase A2 activity was assayed in cellular subfractions isolated from both rabbit kidney medulla and Madin-Darby Canine Kidney cells in the presence of either 1-palmitoyl-2-[1-14C]palmitoyl phosphatidylcholine or 1-stearoyl-2-[1-14C]arachidonyl phosphatidylcholine as substrate. The rate of choline incorporation into glycerolphosphocholine was measured in Madin-Darby Canine Kidney cells growing in the presence of [methyl-3H]choline in the growth medium. Water deprivation of rabbits resulted in an increase of phospholipase A2 activity from 2.7 +/- 0.4 (n = 5) and 5.7 +/- 0.7 (n = 5) to 5.0 +/- 0.8 (n = 5) and 10.8 +/- 1.3 (n = 5) pmol of fatty acid released/min per mg protein in mitochondrial and microsomal fractions, respectively, using dipalmitoyl phosphatidilcholine as substrate while the activity of cytosolic enzyme remained unchanged. Similarly, the addition of sodium chloride in order to increase growth medium osmolality (from 320 mOsm/kg to 520 mOsm/kg) resulted in an elevation of both mitochondrial (from 1.8 +/- 0.1 to 4.9 +/- 0.8 pmol of fatty acid released/min per mg protein, (n = 4) and microsomal (from 8.7 +/- 0.5 to 15.9 +/- 1.7 pmol of fatty acid released/min per mg protein, n = 4) phospholipase A2 activities.(ABSTRACT TRUNCATED AT 250 WORDS)