Mitochondrial calcium uptake and oxygen consumption in cystic fibrosis

Abstract

CYSTIC FIBROSIS (CF), an autosomal recessive exocrinopathy, is characterised by chronic obstructive lung disease and gastrointestinal malabsorption. Reports of exocrine gland secretory anomalies in CF¹ and increased calcium ion concentrations in some CF secretions^2–5, and the importance of cellular Ca to stimulus–secretion coupling⁶ led us to study cellular Ca in CF. We previously reported an enlarged intracellular Ca pool in skin fibroblasts from subjects with CF and obligate heterozygotes, as measured by ⁴⁵Ca exchange into and out of whole cells⁷. We suggested that the altered Ca pool represented a change in mitochondrial Ca. The finding of such an alteration in cells from obligate heterozygotes, who cannot be detected as possessing the CF gene before the birth of a child with CF, suggests that the Ca finding is related to the basic gene defect in CF. The intracellular site of the altered Ca pool or pools could not be identified by studies with whole cells but required measurement of Ca uptake by isolated cell organelles. Here, we report data on Ca uptake studies with mitochondrial and microsomal fractions isolated from skin fibroblasts of subjects with CF and age-, sex- and passage number-matched controls in which mitochondria from CF cells accumulate more Ca than those from control cells. We also describe subsequent studies which show increased mitochondrial electron transport activity, measured as oxygen uptake by whole cells, in cells from subjects with CF and obligate heterozygotes. All experiments were carried out with cells at passage 4–10.