Nifedipine induces apoptosis in cultured vascular smooth muscle cells fromspontaneously hypertensive rats

Apoptosis (programmed cell death) of smooth muscle cells (SMC) in blood ves sels is an essential process involved in the control of vessel wall structu re. Several antihypertensive drugs currently used in therapy may exert thei r pharmacological effects by promoting SMC apoptosis. The biochemical event s which regulate SMC apoptosis in the vessel wall are complex, and not well understood. We therefore investigated whether treatment of cultured SMC fr om normotensive Wistar-Kyoto rats (WKY) and from spontaneously hypertensive rats (SHR) with selected antihypertensive drugs would induce SMC apoptosis . We treated aortic SMC from WKY and SHR in vitro with the L-type Ca2+ chan nel antagonist, nifedipine; with the nitric oxide donor, sodium nitroprussi de (SNAP); with forskolin tan activator of adenylyl cyclase); or with thaps igargin (a selective inhibitor of the sarcoplasmic reticulum (SR), Ca2+-ATP ase); and compared their apoptosis-promoting effects in SMC derived from th e two strains of rats. SMC were derived from the thoracic aorta of 3-4-week -old WKY and SHR, and were used in passages 7-10. Apoptotic cells were dete cted by in-situ end labeling using the terminal deoxynucleotide transferase -mediated dUTP-nick end-labeling (TUNEL) method, and by morphological exami nation. We found that: 1) Treatment of cultured aortic SMC with the L-type Ca2+ channel antagonist, nifedipine (5 x 10(-5) M) for 24 hours induced a s ignificantly higher level of apoptosis in SHR cells than in SMC from WKY. C ells from WKY, following exposure to nifedipine for 72 hours, exhibited a s imilar response to the cells from SHR treated for 24 hours. This was detect able by both morphological criteria as well as DNA labeling by the TUNEL te chnique. 2) Similar treatment of these cells with thapsigargin (1 x 10(-7) M) led to morphological alterations characteristic of apoptotic cells in SM C from both WKY and SHR, and cells from SHR but not WKY were labeled by the TUNEL technique at 2 1 hours. The TUNEL method did however identify cells from both WKY and SHR as apoptotic after 48 and 72 hours of treatment. 3) T he addition of SNAP, or forskolin to the cultured SMC induced significant, but low levels of apoptosis in WKY SMC only. This selective apoptosis-promo ting effect of nifedipine in SHR SMC may result from differences in the con trol of intracellular Ca2+ between the two strains of cells, or it may indi cate that the signaling pathways which regulate apoptosis are different in SMC from the normotensive and the hypertensive rats. Our findings imply tha t SMC apoptosis may be a selective target for pharmacological intervention in hyper-tension. (C) 2000 Elsevier Science Inc. All rights reserved.