UP-REGULATION OF FUNCTIONAL RYANODINE RECEPTORS DURING IN-VITRO AGINGOF HUMAN-DIPLOID FIBROBLASTS

We demonstrate for the first time that cellular aging in vitro is acco mpanied by a dramatic elevation in the levels of ryanodine receptor-be aring Ca2+ channels. These channels normally reside within microsomal membranes and gate Ca2+ release from intracellular stores. We therefor e measured cytosolic Ca2+ levels in 'young' (30 mean population doubli ngs, MPDs) and 'senescent' (53 to 58 MPDs) human diploid fibroblasts ( HDFs). Application of the known. ryanodine receptor modulators, caffei ne or cyclic adenosine diphosphate-ribose (cADPr), triggered cytosolic Ca2+ signals in both young and senescent cells. The signal magnitude however was significantly greater in senescent compared with young HDF s. In parallel, incubation with a highly specific anti-ryanodine recep tor antiserum resulted in specific immunofluorescence only in senescen t HDPs. We envisage that elevated levels of functional ryanodine recep tors may underlie the defective Ca2+ handling and cellular degeneratio n that occurs with aging. (C) 1998 Academic Press.