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

Department of Pharmacology, University of Vermont, Burlington, Vermont 05405 Submitted 30 November 2004 ; accepted in final form 15 August 2005 Vascular damage signals smooth muscle cells to proliferate, often exacerbating existing pathologies. Although the role of changes in "global" Ca 2+ in vascular smooth muscle (VSM) cell dedifferentiation has been studied, the role of specific Ca 2+ signals in determining VSM phenotype remains relatively unexplored. Earlier work with cultured VSM cells suggests that inositol 1,4,5-trisphosphate receptor (IP 3 R) expression and sarcoplasmic reticulum (SR) Ca 2+ release may be linked to VSM cell proliferation in native tissue. Thus we hypothesized that SR Ca 2+ release through IP 3 Rs 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 Ca 2+ 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 Ca 2+ waves in myocytes in the arteries that were blocked by the IP 3 R antagonist 2-aminoethoxydiphenylborate (2-APB). Inhibition of IP 3 R opening (via 100 µM 2-APB, 10 µM xestospongin C, or 25 µM U-73122) dramatically reduced outgrowth cell number compared with untreated or ryanodine-treated (10 µM) 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 IP 3 R Ca 2+ release is required for VSM cell proliferation in these arteries. calcium signaling; explant culture; calcium channels; sarcoplasmic reticulum Address for reprint requests and other correspondence: M. K. Wilkerson, Dept. of Pharmacology, Univ. of Vermont College of Medicine, 89 Beaumont Ave., Burlington, VT 05405-0068 (e-mail: keith.wilkerson{at}uvm.edu )