Effects of phospholipase C on the Na+-Ca2+ exchange and Ca2+ permeability of cardiac sarcolemmal vesicles.
We have examined the effects of phospholipase C pretreatment on Ca2+ transport in highly purified canine cardiac sarcolemmal vesicles. Na+-Ca2+ exchange, measured as Nai+-dependent Ca2+ uptake, is stimulated when 10-70% of the membrane phospholipid has been hydrolyzed. Although the phospholipase C treatment also increases sarcolemmal passive Ca2+ flux, the membrane maintains a sufficient permeability barrier for enhanced transport (via Na+-Ca2+ exchange) to be observed. These effects can be obtained with phospholipase C from either Clostridium perfringens or Bacillus cereus. We find that the phospholipase C (C. perfringens) preferentially hydrolyzes phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin leaving the negatively charged phospholipids, phosphatidylserine and phosphatidylinositol, intact. This suggests that the presence of negatively charged phospholipids is sufficient to ensure Na+-Ca2+ exchange activity. Thin section electron microscopy reveals gross morphological changes in phospholipase C-treated sarcolemma. The vesicles are aggregated and diacylglycerol droplets are visible. Fusion occurs such that adjacent vesicles share a common bilayer. It is surprising that vesicles displaying severe structural damage can demonstrate enhanced transport activity.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D008854:Microscopy, Electron; D009206:Myocardium / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism* / Q000648:ultrastructure; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*
D012964:Sodium; D010740:Phospholipases; D010738:Type C Phospholipases; D002118:Calcium