Mechanical stress stimulates phospholipase C activity and intracellular calcium ion levels in neonatal rat cardiomyocytes

To investigate how mechanical stress is sensed by cardiomyocytes and translated to cardiac hypertrophy, cardiomyocytes were subjected to stretch while measuring phospholipase C (PLC) and phospholipase D (PLD) activities and levels of intracellular calcium ions (Ca2+]i) and pH.In stretched cardiomyocytes, PLC activity increased 2-fold after 30 min, whereas PLD activity hardly increased at all. Mechanical stress induced by prodding or by cell stretch increased Ca2+](i)by a factor 5.2 and 4, respectively. Gadolinium chloride (stretch-activated channel blocker) attenuated the prodding-induced and stretch-induced Ca2+](i)rise by about 50%. Blockade of ryanodine receptors by a combination of Ruthenium Red and procaine reduced the Ca2+](i)rise only partially. Diltiazem (L-type Ca2+ channel antagonist) blocked the prodding-induced Ca2+](i)rise completely, and reduced the stretch-induced Ca2+](i)rise by about 50%. The stretch-induced Ca2+](i)rise was unaffected by U73122, an inhibitor of PLC activity. Stretch did not cause cellular alkalinization.In conclusion, in cardiomyocytes, PLC and Ca2+](i)levels are involved in the stretch-induced signal transduction, whereas PLD plays apparently no role. The stretch-induced rise in Ca2+](i)in cardiomyocytes is most probably caused by Ca2+](i)influx through L-type Ca2+ channels and stretch-activated channels, leading to Ca2+-induced Ca2+ -release from the SR via the ryanodine receptor.