Regulation of store-operated Ca 2+ entry in pulmonary artery smooth muscle cells

Abstract

Store-operated Ca 2+ entry (SOCE) is an important mechanism for Ca 2+ influx in smooth muscle cells; however the activation and regulation of this influx pathway are incompletely understood. In the present study we have examined the effect of several protein kinases in regulating SOCE in pulmonary artery smooth muscle cells (PASMCs) of the rat. Inhibition of protein kinase C with chelerythrine (3 μM) potentiated SOCE by 47 ± 2%, while the tyrosine kinase inhibitors genistein (100 μM) and tyrphostin 23 (100 μM) caused a significant reduction in SOCE of 55 ± 9% and 43 ± 7%, respectively. It has been proposed that Ca 2+-insensitive phospholipase A 2 (iPLA 2) is involved in the activation of SOCE in many different cell types. The iPLA 2 inhibitor, bromoenol lactone had no effect on SOCE, suggesting that this mechanism was not involved in the activation of the pathway. The calmodulin antagonists, calmidazolium (CMZ) (10 μM) and W-7 (10 μM) appeared to potentiate SOCE in PASMCs. Further investigation established that CMZ was actually activating a Ca 2+ influx pathway that was independent of the filling state of the sarcoplasmic reticulum. The CMZ-activated Ca 2+ influx was blocked by Gd 3+ (10 μM), but unaffected by 2-APB (75 μM), indicating a pharmacological profile distinct from the classical SOCE pathway.