| Autor: |
Saumon, Georges, Basset, Guy, Bouchonnet, Francine, Crone, Christian |
| Zdroj: |
Pflügers Archiv: European Journal of Physiology; 1989, Vol. 414 Issue 3, p340-345, 6p |
| Abstrakt: |
Alveolar fluid absorption is greatly enhanced by cAMP and by β-adrenergic agonists via an increase in Na transport. Little is known about K homeostasis under these circumstances. We studied K transport across alveolar epithelium in isolated perfused rat lungs stimulated either by dibutyryl-cAMP or isoproterenol. K fluxes and the apparent permeability ofRb across the epithelium (alveoli to plasma) were interpreted according to a model involving two types of cells, B and L, distinguished by the location of Na−K-ATPases (basal and luminal). Water is considered to be absorbed by B cells in a solute-coupled process energized by a basolateral Na−K-ATPase that is stimulated by isoproterenol and cAMP. K transport out of the alveoli is due to the activity of a Na−K-ATPase located in the apical membrane of L cells. In the present study net transport rate of K was −0.5±0.15 nmol/s, n=20 (out of alveoli) in control conditions. When the epithelium was stimulated by dibutyryl-cAMP (10 mol/l) net absorption of K reversed to net 'secretion' into alveoli (3.2±0.31 nmol/s), fluid absorption was not stimulated. K 'secretion' was abolished by apical Ba, indicating it was due to opening of apical K channels. Basolateral ouabain reversed net K 'secretion' to net absorption indicating that K entry into alveoli was dependent on activity of B cell basolateral Na−K-ATPase (masking simultaneous K removal by apical L cell Na−K-pump). When larger concentrations of dibutyryl-cAMP (10 mol/l) or when isoproterenol were used to stimulate the epithelium there was a tripling of fluid absorption. In this situation a biphasic response of K transport was observed. Initially, net K influx similar to that observed in 10 mol/l dibutyryl-cAMP experiments occurred, followed by a large K efflux from alveolar spaces. This may reflect stimulation of apical Na−K-ATPase in L cells, combined with partial closure of apical K channels in B cells. The variations of the apparent permeability ofRb, measured from alveoli to plasma, reinforce this interpretation of the mechanisms of K transport. Our results suggest that K transport across alveolar epithelium is modulated by isoproterenol and cAMP, by stimulation of Na−K-ATPase in B and L cells supplemented by control of K channels. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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