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Objectives: Mucus clearance is an important component of the lungs innate defence against diseases. The ability of the airways to clear mucus is strongly dependent on the rate of ciliary beating and the hydration state of the airway surface liquid (ASL). The aims of this study were (i) to determine physiological mechanisms and rates of ion transport and (ii) to show the influence of respiratory infections on active ion transport mechanisms in calves.
Methods: The airway mucosa of 4 adult cows, 8 healthy calves, 18 calves experimentally infected with Mycoplasma (M.) bovis, and 1 calf with chronic pneumonia was dissected and mounted as flat sheets in Ussing chambers. Under short circuit conditions, resistance (Rt), current (Isc), voltage (PD) were measured. Both the unidirectional mucosa(m)-to-serosa(s) and s-to-m fluxes (Jms, Jsm) of Sodium (Na), Chloride (Cl) and Mannitol (Jms) were determined.
Results: Under short circuit conditions, there was a net flow of Na in the absorptive (m→s) direction and a net movement of Cl in the opposite (s→m) direction in both cows and calves. In calves, the s-to-m Na transport was significantly higher and therefore the net absorption was significantly lower compared to cows. The Cl secretion was nearly equal in both, calves and cows, but the Cl transport in calves was significantly higher. Calves showed also a significantly higher paracellular (Mannitol) movement. The sum of both net fluxes, Cl and Na, was calculated from matched experiments and was found to be slightly, but significantly different from the measures Isc. Probably there is a transport of HCO3-. In M. bovis-infected calves (subclinical model) ion fluxes were determined 3, 7, 10, 14, 21 and 35 days post infection (p.i.). It was shown that neither Na- and Cl- nor Mannitol-fluxes changed during the first 35 days p.i.. Addition of amiloride, a Na blocker (Na channel ENAC and Na/H-exchanger NHE), caused continuously decreased reactivity in Isc over 35 days from 14,37 % to 5,46 % and had nearly no effect in some tissues. Only 2 animals showed mild cough and nasal discharge at the day of section (day 7-10). Compared to calves without cough and nasal discharge, the Na transport (Jms, Jsm) in calves with cough and nasal discharge was lower but the net Na absorption was nearly equal in both. There was no difference in Cl transport but a significant lower transport of paracellular mannitol in calves with cough and nasal discharge. The chronic purulent bronchopneumonia caused by parainfluenza virus type 3 and Pasteurella multocida of a calf caused under short-circuit conditions a significant increase in JsmCl, indicating changes in net secretion of Cl, and the paracellular transport of 3-H-Mannitol decreased significantly. The Na transport was higher but the net absorption of Na was not affected.
1. The active ion transport differs age-dependent.
2. Respiratory infections cause a change in active ion transport.
3. The change of active ion transport and clinical symptoms act simultaneously.
4. Tight-junctions are tighter in calves with clinical signs.
5. Probably M. bovis influences the apical Na-channel.