PROTOCOLS FOR IN-VIVO MEASUREMENT OF THE ION-TRANSPORT DEFECTS IN CYSTIC-FIBROSIS NASAL EPITHELIUM

New treatments for cystic fibrosis (CF), including gene therapy, are currently being assessed. These aim to correct the basic defects of increased sodium absorption and decreased chloride secretion in airway epithelia Assessment of these bioelectric parameters, particularly in the nasal epithelium, is likely to be used as a measure of treatment efficacy. However, the optimal in vivo protocol to discriminate cystic fibrosis from non-cystic fibrosis subjects is unclear. We have, therefore, compared three protocols for measurement of the cystic fibrosis ion transport defects in vivo in the nasal epithelium. Sodium absorption was measured using both the baseline potential difference and the response to the sodium channel blocker, amiloride. Chloride secretion was assessed in the presence of amiloride, using perfusion with isoprenaline, or terbutaline, or a low chloride solution followed by isoprenaline. Baseline potential difference (PD) and the absolute response to amiloride clearly differentiated the increased sodium absorption in the cystic fibrosis subjects. The responses both to terbutaline (Delta PD: non-CF: -0.8 (SEM 0.7) mV; CF: -3.6 (0.5) mV) and isoprenaline (non-CF: 15 (0.6) mV; CF: -2.9 (0.6) mV) differentiated the two groups of subjects, but there was considerable overlap of values. Perfusion with a low chloride solution (non-CF: 12.6 (1.2) mV; CF: 0.6 (0.4) mV), as well as subsequent perfusion with isoprenaline (non-CF: 10.0 (1.1) mV; CF: -1.4 (0.4) mV) allowed clear separation of the two groups, with no overlap of values. Some CF subjects showed a transient hyperpolarization to these stimuli, which could clearly be differentiated from the sustained responses seen in non-cystic fibrosis subjects. We conclude that sodium hyperabsorption in the nasal epithelium of cystic fibrosis subjects can be reliably assessed using the baseline potential difference and the absolute change following amiloride. The defect in chloride secretion may be clearly measured (in the presence of amiloride) by perfusion with a low chloride solution followed by isoprenaline. We suggest that this protocol is appropriate for in vivo assessment of new treatments for cystic fibrosis.