Simplified PD measurement using directly connectable electrodes for superfusion

Schüler D, Weber K, Moerkerk W, Hüls G, Lindemann H; Children`s hospital of Giessen/Germany
XIII. International Cystic Fibrosis Congress, 4 - 8 June 2000, Stockholm

Introduction:

An easy and reliable measurement of potential difference (PD) by means of superfusion (SF) would be of interest for routine use in the diagnostic field of cystic fibrosis [1]. The conventional device involves a sophisticated system of agar gel bridges to avoid offset potentials [2]. Our aim was to make available an easier method for PD measurement using electrodes which are directly connectable with the flow-through system needed for SF [3].

Methods:

To validate this technique the nasal transepithelial PD measured with Ag/AgCl electrodes (WPIâ , Berlin, Germany) connected by a luer lock port with the flow-through system and with conventional device using agar gel bridges between the Ag/AgCl electrodes (Ingoldâ , Steinbach, Germany) and the flow-through system (Fig. 1) was compared in 15 CF-patients and 34 healthy subjects (12-61 years).
During one measurement PD values were simultaneously or alternately recorded with both methods (Fig. 2).
Prior to use the zero offset of electrodes was determined; values greater than 2 mV were not found. The electrodes exhibit stable and reproducible potentials within six months, when stored in KCl solution.

Figure 1: Scheme of nasal PD measurement with flow-through electrodes: conventional agar gel bridges (left) and new device (right)

 


Figure 2: Representative time course of nasal PD using SF, recorded with the conventional method (above) and the new device (below)

 Results:

Comparison of basal PD (r=1,0; p<0,0001) (Fig. 3) and PD after SF with several drugs (Fig. 4) showed identical values.
There was a significant increase of PD after SF with b -mimetic in healthy subjects (86±32%,8 ±SD) compared to CF-patients (-5,7±14%,8 ±SD) without overlapping of both groups (Fig. 4).

Figure 3: Correlation between nasal PD measured with conventional agar gel bridges and with directly connectable electrodes

Figure 4:  Boxplot of delta PD(%) after superfusion (SF) with beta-mimetic using the conventional device and the new device, respectively.

Conclusions:

Using electrodes directly connectable with the flow-through system simplifies the PD measurement and the maintenance of it. The new device does not impair the diagnostic value of PD measured by superfusion method in vivo. Furthermore, it is a suitable performance for routine use.
Both methods revealed a clear separation between impaired activation of chloride channels in CF-patients and a regular chloride secretion in healthy subjects.
There is no overlap between CF and non CF.

References

[1] Hofmann T, Böhmer O, Hüls G, Terbrack H, Bittner P, Klingmüller V, Heerd E, Lindemann H (1997) Am J Respir Crit Care Med 155(6):1908-13
[2] Boucher RC, Bromberg PA, Gatzy JT (1980) J Appl Physiol Respirat Environ Exercise Physiol, 48(1):169-76
[3] Kersting U, Schwab A, Hebestreit A (1998) Am J Physiol, 275 (Adv. Physiol. Educ.20):72-77