Hypoxic remodelling of Ca 2+ stores does not alter human cardiac myofibroblast invasion

Abstract

Cardiac fibroblasts are the most abundant cell type in the heart, and play a key role in the maintenance and repair of the myocardium following damage such as myocardial infarction by transforming into a cardiac myofibroblast (CMF) phenotype. Repair occurs through controlled proliferation and migration, which are Ca 2+ dependent processes, and often requires the cells to operate within a hypoxic environment. Angiotensin converting enzyme (ACE) inhibitors reduce infarct size through the promotion of bradykinin (BK) stability. Although CMF express BK receptors, their activity under the reduced O 2 conditions that occur following infarct are entirely unexplored. Using Fura-2 microfluorimetry on primary human CMF, we found that hypoxia significantly increased the mobilisation of Ca 2+ from intracellular stores in response to BK whilst capacitative Ca 2+ entry (CCE) remained unchanged. The enhanced store mobilisation was due to a striking increase in CMF intracellular Ca 2+-store content under hypoxic conditions. However, BK-induced CMF migration or proliferation was not affected following hypoxic exposure, suggesting that Ca 2+ influx rather than mobilisation is of primary importance in CMF migration and proliferation.