Biosynthesis of platelet-activating factor. VI. Precursor of platelet-activating factor and acetyltransferase activity in isolated rat kidney cells

Abstract

Isolated glomeruli and tubular and medullary cells obtained from perfused kidneys from Wistar rats were stimulated with ionophore A 23187 (0.5 to 6 microM) or kept overnight at pH 9.5. The amount of platelet-activating factor (Paf-acether) formed was measured in the ethanolic cell extracts using aggregation of washed rabbit platelets. 2-Lyso Paf-acether present in cells was transformed into Paf-acether by chemical acetylation and measured in the same manner as Paf-acether. Microsomes from glomeruli and medullary and tubular cells were prepared, and the acetyltransferase activity was measured. Paf-acether was formed in a dose-dependent fashion by glomeruli and medullary cells, and maximal formation with 3 microM ionophore A 23187 was 1.9 +/- 0.2 and 1.1 +/- 0.2 pmoles/mg of protein, respectively. Paf-acether was not recovered from tubular cells. Three cell types produced large amounts of 2-lyso Paf-acether when incubated at alkaline pH. Only glomeruli generated appreciable quantity of 2-lyso Paf-acether upon ionophore A 23187 stimulation. The acetyltransferase specific activities in ionophore A 23187-stimulated glomeruli and medullary and tubular cells were 3.8 +/- 0.8, 0.3 +/- 0.1, and 0.2 +/- 0.1 nmoles of Paf-acether/10 min/mg of protein, respectively. This study demonstrates the formation of Paf-acether by two distinct populations of kidney cells, pointing out the glomerular cells, besides the already known medullary cells, as capable of forming Paf-acether.