Apoptosis in cultured midgut cells from heliothis virescens larvae exposed to various conditions

We exposed midgut cells from primary cultures of Heliothis virescens larvae to cell-free previously used medium, the Vaughn X and HyQ SFtrade mark media used for serum-free culture of insect cell lines which do not support H. virescens midgut cells, and to toxin from Bacillus thuringiensis. A statistically significant increase in the percent of dying cells was counted in cell populations in Vaughn X medium. Use of the TUNEL method to detect apoptosis indicated a low rate (7.2%) of apoptosis in control cultures grown in Heliothis medium, an increase to approximately 20% in previously used and HyQ SFtrade mark media, and to approximately 45% of cells remaining after exposure to and initial destruction by B. thuringiensis toxin. Apoptotic nuclei were predominant (approximately 6%) in mature columnar cells in control cultures. Approximately 1% of goblet, stem, and differentiating cells were apoptotic. However, apoptosis rose to 12% in stem and differentiating cells exposed to used and unsuitable medium. B. thuringiensis exposure to toxin for 2-3 days resulted in visible membrane damage and necrosis, causing the death of 84% of the cells as measured by both the TUNEL and Annexin methods. Some of the columnar cells and stem and differentiating cells that remained also contained apoptotic nuclei. Stem and differentiating cells normally replace dying mature cells in the midgut. Thus, exposure of cultures of H. virescens midgut cells to adverse environments such as unsuitable or poisonous media appeared to induce down-regulation of the cell populations by apoptosis.