Cell Calcium Levels of Normal and Cystic Fibrosis Nasal Epithelium

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Abstract
To determine whether epithelial ion transport abnormalities in cystic fibrosis (CF) might reflect abnormal regulation of intracellular Ca2+ levels, cytosolic free calcium (Cai2+) was measured using fura-2 or quin2 in suspensions of normal or CF nasal epithelial cells derived from primary cell culture. The basal Cai2+ level measured with fura-2 in CF nasal epithelia was 155 ± 9 nM (n = 5), a value not significantly different from normal nasal epithelia (143 ± 16 nM, n = 5). Total cell calcium was measured by atomic absorption spectroscopy and no differences were observed between CF (6.3 ± 0.5 nmol/mg protein; n = 3) and normal (6.2 ±1.2 nmol/mg protein; n = 3) nasal epithelial cells. Placing Na+ loaded cells in a low (10 mM) extracellular Na+ solution resulted in a rapid increase in Cai2+ consistent with Ca2+ uptake via a plasmalemmal Na+-Ca2+ exchanger. The level of Cai2+ achieved by this low Na+ maneuver was not significantly different in CF cells compared to normal cells. Neither isoproterenol (10-5 M) nor forskolin (10-6 M) had any effect on Cai2+ in normal or CF nasal epithelial cells. Thus, it appears that differences in cell Cai2+, as measured by fluorescent chelators in suspensions of cultured cells, do not account for the abnormalities in basal or isoproterenol stimulated ion transport in CF tissues.