Nifedipine does not induce but rather prevents apoptosis in cardiomyocytes

Abstract

The potential of Ca 2+ channel antagonists, particularly nifedipine, to cause apoptotic cell death has been controversial and is of considerable importance for cardiomyocytes as loss of these cells is an important component of the pathophysiology leading to heart failure. To examine the hypothesis that nifedipine induces cell death and modulates calcium-induced apoptosis, cardiomyocytes in culture from embryonic chick hearts, that readily manifest apoptosis, were studied. Apoptosis was evaluated by fluorescent activated cell sorting (FACS) analysis and by quantitative analysis of DNA fragmentation by an enzyme-linked immunosorbent assay (ELISA) specific for histone-associated DNA fragments of mono- and oligonucleosome size. Cell death was evaluated by using the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay. Cardiomyocytes were treated with various concentrations of nifedipine over a concentration range relevant to serum concentrations in man. Nifedipine, 1 to 100 μM, did not produce cell death in cardiomyocytes. There was no evidence of apoptosis on FACS analysis of cardiomyocytes stained with fluoresceine diacetate or propidum iodide (PI). Neither was there any evidence of apoptotic nuclei on PI staining of permeabilized cardiomyocytes treated with nifedipine. In contrast, DNA fragmentation consistent with apoptosis was induced in a significant ( P<0.05) concentration-dependent manner, by increases in extracellular Ca 2+ concentration ([Ca 2+] o). Importantly, nifedipine reduced DNA fragmentation produced by increased [Ca 2+] o. Furthermore, nifedipine blocked calcium-induced cell death as high [Ca 2+] o significantly ( P<0.05) reduced cell viability. These data indicate that nifedipine does not induce apoptosis in cardiomyocytes rather apoptosis in cardiomyocytes is under regulatory control by Ca 2+ and nifedipine can antagonize Ca 2+-mediated apoptotic cell death.