Mechanical stimulation of skeletal muscle generates lipid‐related second messengers by phospholipase activation

Abstract

Repetitive mechanical stimulation of cultured avian skeletal muscle increases the synthesis of prostaglandins (PG) E₂ and F_2α which regulate protein turnover rates and muscle cell growth. These stretch‐induced PG increases are reduced in low extracellular calcium medium and by specific phospholipase inhibitors. Mechanical stimulation increases the breakdown rate of ³H‐arachidonic acid labelled phospholipids, releasing free ³H‐arachidonic acid, the rate‐limiting precursor of PG synthesis. Mechanical stimulation also increases ³H‐arachidonic acid labelled diacylglycerol formation and intracellular levels of inositol phosphates from myo‐[2‐³H]inositol labelled phospholipids. Phospholipase A₂ (PLA₂), phosphatidylinositol‐specific phospholipase C (PLC), and phospholipase D (PLD) are all activated by stretch. The stretch‐induced increases in PG production, ³H‐arachidonic acid labelled phospholipid breakdown, and ³H‐arachidonic acid labelled diacylglycerol formation occur independently of cellular electrical activity (tetrodotoxin insensitve) whereas the formation of inositol phosphates from myo‐[2‐³H]inositol labelled phospholipids is dependent on cellular electrical activity. These results indicate that mechanical stimulation increases the lipid‐related second messengers arachidonic acid, diacylglycerol, and PG through activation of specific phospholipases such as PLA₂ and PLD, but not by activation of phosphatidylinositol‐specific PLC.