Ca2+ handling is altered when arterial myocytes progress from a contractile to a proliferative phenotype in culture

Phenotypic modulation of vascular myocytes is important for vascular development and adaptation. A characteristic feature of this process is alteration in intracellular Ca2+ handling, which is not completely understood. We studied mechanisms involved in functional changes of inositol 1,4,5-trisphosphate (IP3)- and ryanodine (Ry)-sensitive Ca2+ stores, store-operated Ca2+ entry (SOCE), and receptor-operated Ca2+ entry (ROCE) associated with arterial myocyte modulation from a contractile to a proliferative phenotype in culture. Proliferating, cultured myocytes from rat mesenteric artery have elevated resting cytosolic Ca2+ levels and increased IP3-sensitive Ca2+ store content. ATP- and cyclopiazonic acid [CPA; a sarco(endo) plasmic reticulum Ca2+-ATPase (SERCA) inhibitor]- induced Ca2+ transients in Ca2+-free medium are significantly larger in proliferating arterial smooth muscle cells (ASMCs) than in freshly dissociated myocytes, whereas caffeine (Caf)-induced Ca2+ release is much smaller. Moreover, the Caf/Ry-sensitive store gradually loses sensitivity to Caf activation during cell culture. These changes can be explained by increased expression of all three IP3 receptors and a switch from Ry receptor type II to type III expression during proliferation. SOCE, activated by depletion of the IP3/CPA-sensitive store, is greatly increased in proliferating ASMCs. Augmented SOCE and ROCE (activated by the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol) in proliferating myocytes can be attributed to upregulated expression of, respectively, transient receptor potential proteins TRPC1/4/5 and TRPC3/6. Moreover, stromal interacting molecule 1 (STIM1) and Orai proteins are upregulated in proliferating cells. Increased expression of IP3 receptors, SERCA2b, TRPCs, Orai(s), and STIM1 in proliferating ASMCs suggests that these proteins play a critical role in an altered Ca2+ handling that occurs during vascular growth and remodeling.