Occurrence of phospholipase A₂ and lysophospholipase in a gastric H, K‐ATPase‐containing membrane fraction, and the formation of lysophosphatidylcholine in stimulated pig parietal cells

Abstract

A membrane fraction containing H,K-ATPase (EC 3.6.1.36) was prepared from pig gastric mucosa and found to contain phospholipase A2 (EC 3.1.1.4) and lysophospholipase (EC 3.1.1.5) activities. Washing the membranes decreased their protein content by 25%. Recovery profiles of H,K-ATPase, phospholipase A2 and lysophospholipase were similar for membranes washed either with water or with 0.15 or 1.5 M KCl. Nearly identical distribution profiles were obtained for the three enzyme activities after centrifugation of washed vesicle membranes on a linear sucrose gradient. The phospholipase A2 activity was stimulated by calcium and increased further in the presence of calmodulin. The amount of cellular radioactively labelled lysophosphatidylcholine was doubled upon cholinergic stimulation of isolated parietal cells prelabelled with [3H]glycerol or 32Pi. The liberated lyso[32P]phosphatidylcholine had its acyl chain in the sn-1 position, which implies an activation of a phospholipase A2. These findings indicate that secretagogues which increase the cytosolic Ca2+ concentration, i.e. acetylcholine, histamine and gastrin, may activate a phospholipase A2 in the parietal cell.

A continuous‐flow technique for analysis of stoichiometry and transport kinetics of gastric H, K‐ATPase

“…Although the H,K-ATPase 94-kDa peptide is the dominating component in the preparation of gastric vesicles, these have been reported also to contain a membrane-bound Ca2+-and calmodulin-dependent phospholipase A, (Olaisson et al 1990). The products of this enzyme, lysophospholipids and long-chain fatty acids such as arachidonic acid, have been shown to inhibit cation-transport ATPases (Im & Blakeman 1982, Im et al 1987, Tamura et al 1987) and might even, at high concentrations, produce leakage of ions and disruption of the vesicles because of their amphiphilic properties.…”

Purification and characterization of guinea pig gastric phospholipase A2 of the pancreatic type

“…This latter location of the enzyme tends to favor a role for the PLA, at those sites. Very recently, Olaisson et al [36] reported that PLA, activity was associated with membrane fractions enriched in H, K-ATPase, which catalyzes acid secretion and is a marker enzyme for the apical and tubulovesicular membranes of the parietal cells. They also suggested that PLA, participated in calciumenhanced fusion of the H, K-ATPase containing membrane vesicles [37].…”