DEFECTIVE ENDOTHELIUM-DEPENDENT RELAXATION OF VASCULAR SMOOTH-MUSCLE AND ENDOTHELIAL-CELL CA2-ATPASE ISOFORM-3( SIGNALING IN MICE LACKING SARCO(ENDO)PLASMIC RETICULUM CA2+)

Sarco(endo)plasmic reticulum Ca2+ ATPase isoform 3 (SERCA3) is one of two Ca2+ pumps serving intracellular Ca2+ signaling pools in non-muscl e tissues; however, unlike the ubiquitous SERCA2b, it exhibits a restr icted cell-type distribution. Gene targeting was used to generate a mo use with a null mutation in the SERCA3 gene, Homozygous mutant mice we re viable, fertile, and did not exhibit an overt disease phenotype. Be cause SERCA3 is expressed in arterial endothelial cells, aortic ring p reparations were analyzed to determine whether it is involved in the r egulation of vascular tone, Contraction-isometric force relations in r esponse to phenylephrine or KCl, as well as relaxation produced by exp osure to a nitric oxide donor, were similar in wild-type and null muta nt aortas, Acetylcholine-induced endothelium-dependent relaxation of a ortas after precontraction with phenylephrine was significantly reduce d in homozygous mutants (61.3 +/- 5.6% in wild type, 35.4 +/- 7.3% in mutants). Ca2+ imaging of cultured aortic endothelial cells demonstrat ed that the acetylcholine-induced intracellular Ca2+ signal is sharply diminished in SERCA3-deficient cells and also indicated that replenis hment of the acetylcholine-responsive Ca2+ stores is severely impaired . These results indicate that SERCA3 plays a critical role in endothel ial cell Ca2+ signaling events involved in nitric oxide-mediated relax ation of vascular smooth muscle.