Functional nucleotide receptor expression and sarcoplasmic reticulum morphology in dedifferentiated porcine coronary smooth muscle cells

The phenotypic dedifferentiation of vascular smooth muscle cells (SMCs) is an early event associated with cell culturing and vascular injury. The purp ose of this study was to evaluate the SMC phenotype underlying the function al responsiveness of SMCs to nucleotides in organ culture. Porcine coronary arteries were either used fresh, cold stored (5 degreesC) 4 days, or organ cultured (37 degreesC) 4 days. Fura-2 digital imaging of single SMCs was u sed to measure the myoplasmic calcium (Ca-m) response to 10 muM of the foll owing. nucleotide receptor agonists: UTP, UDP, ATP, ADP, and 2-MeSATP. In c ontrast to the nucleotides UDP, ATP, ADP; and 2-MeSATP, the Cam response in creased 10-fold. and the number of cells that responded to UTP increased 5- fold in SMCs from organ culture compared to SMCs from fresh or cold-stored arteries. Simultaneous imaging of Cam, DNA content, and SR distribution in SMCs from organ culture indicated that the UTP-induced Ca-m increase occurr ed exclusively in SMCs that had a dedifferentiated cell phenotype. Three-di mensional image reconstruction of the nucleus and sarcoplasmic reticulum (S R) revealed a novel transnuclear SR distribution that intertwined with the nucleus in fresh SMCs, while in SMCs from organ culture the SR was predomin antly perinuclear and cytoplasmic. This study demonstrates that the functio nal up-regulation of UTP-sensitive receptors and the disappearance of the t ransnuclear SR distribution are novel features of dedifferentiated coronary SMCs. Copyright (C) 2001 S. Karger AG, Basel.