Inositol trisphosphate receptor calcium release is required for cerebral artery smooth muscle cell proliferation.

Vascular damage signals smooth muscle cells to proliferate, often exacerbating existing pathologies. Although the role of changes in "global" Ca2+ in vascular smooth muscle (VSM) cell dedifferentiation has been studied, the role of specific Ca2+ signals in determining VSM phenotype remains relatively unexplored. Earlier work with cultured VSM cells suggests that inositol 1,4,5-trisphosphate receptor (IP3R) expression and sarcoplasmic reticulum (SR) Ca2+ release may be linked to VSM cell proliferation in native tissue. Thus we hypothesized that SR Ca2+ release through IP3Rs in the form of discrete transient signals is necessary for VSM cell proliferation. To investigate this hypothesis, we used mouse cerebral arteries to design an organ culture system that permitted examination of Ca2+ dynamics in native tissue. Explanted arteries were cultured in normal medium with 10% FBS, and appearance of individual VSM cells migrating from explanted arteries (outgrowth cells) was tracked daily. Initial exposure to 10% FBS increased Ca2+ waves in myocytes in the arteries that were blocked by the IP3R antagonist 2-aminoethoxydiphenylborate (2-APB). Inhibition of IP3R opening (via 100 microM 2-APB, 10 microM xestospongin C, or 25 microM U-73122) dramatically reduced outgrowth cell number compared with untreated or ryanodine-treated (10 microM) arteries. Consistent with this finding, 2-APB inhibited cell proliferation, as measured by reduced proliferating cell nuclear antigen immunostaining within 48 h of culture but did not inhibit cell migration. These results indicate that activation of IP3R Ca2+ release is required for VSM cell proliferation in these arteries.