Lipid methylation, hormone action and compensatory hypertrophy in renal cortical tubules

Lipid methylation has been studied in homogenized dog kidney cortical tubules. At pH 9, using S-adenosyl-L-methionine as methyl donor, most of the methyl groups appeared incorporated into phosphatidylcholine, the activity showing an apparent Km of 16 microM. This enzymatic activity was unchanged by the presence of the divalent cations Ca2+ or Mg2+, cAMP or cGMP. In addition, lipid methylation was also unchanged after treatment of intact tubules with angiotensin II, parathyroid hormone or vasopressin. An increased phosphatidylcholine synthesis was observed in the remnant kidney cortical tubules after uninephrectomy through an activation of phosphocholine transferase without detectable modification of lipid methylation. These findings suggest that lipid methylation is not regulated by these biochemical or functional stimuli tested in canine renal cortical tubules.