Modulation of Ca2+-Activated Cl− Secretion by Basolateral K+ Channels in Human Normal and Cystic Fibrosis Airway Epithelia

Abstract

Human airway epithelia express Ca2+-activated Cl- channels (CaCC) that are activated by extracellular nucleotides (ATP and UTP). CaCC is preserved and seems to be up-regulated in the airways of cystic fibrosis (CF) patients. In the present study, we examined the role of basolateral K+ channels in CaCC-mediated Cl- secretion in native nasal tissues from normal individuals and CF patients by measuring ion transport in perfused micro Ussing chambers. In the presence of amiloride, UTP-mediated peak secretory responses were increased in CF compared with normal nasal tissues. Activation of the cAMP pathway further increased CaCC-mediated secretion in CF but not in normal nasal mucosa. CaCC-dependent ion transport was inhibited by the chromanol 293B, an inhibitor of cAMP-activated hKvLQT1 K+ channels, and by clotrimazole, an inhibitor of Ca2+-activated hSK4 K+ channels. The K+ channel opener 1-ethyl-2-benzimidazolinone further increased CaCC-mediated Cl- secretion in normal and CF tissues. Expression of hSK4 as well as hCACC-2 and hCACC-3 but not hCACC-1 was demonstrated by reverse transcriptase PCR on native nasal tissues. We conclude that Ca2+-activated Cl- secretion in native human airway epithelia requires activation of Ca2+-dependent basolateral K+ channels (hSK4). Co-activation of hKvLQT1 improves CaCC-mediated Cl- secretion in native CF airway epithelia, and may have a therapeutic effect in the treatment of CF lung disease.

Regulation of ENaC and CFTR expression with K+channel modulators and effect on fluid absorption across alveolar epithelial cells

“…Indeed, voltage-dependent K ϩ KvLQT1 channels and calciumactivated K ϩ (K Ca ) channels have been identified as key elements of ion transport. A severe reduction of Cl Ϫ secretion has been reported after inhibition of KvLQT1 and intermediate-conductance, calcium-activated K ϩ (IK Ca ) channels in nasal and bronchial cells (12,34,35). More interestingly, it has been observed that IK Ca channel openers stimulate Cl Ϫ secretion in Calu-3 cells (16,56), in primary cultures of human bronchial epithelia (56), and in nasal cells (35).…”

Bestrophin-1 Enables Ca2+-activated Cl− Conductance in Epithelia

“…Previous studies showed that (i) application of the Ca 2ϩ ionophore ionomycin also activates Cl Ϫ secretion; (ii) in the presence of low (1 M) extracellular Ca 2ϩ , activation of Cl Ϫ secretion is very transient; (iii) after inhibition of phospholipase C, purinergic Cl Ϫ secretion is reduced; and (iv) DIDS inhibits Ca 2ϩ -activated Cl Ϫ secretion in mouse airways (18). These and other experiments (19) Both CFTR and CaCC control airway surface liquid, which is essential for mucociliary clearance (27). Purinergic activation of CaCC in the airways resembles an important therapeutic principle for cystic fibrosis (28,29).…”

“…Cl Ϫ secretion in mouse airways is dominated by CaCC, which explains why CFTR knock-out animals do not develop a cystic fibrosis lung disease (21). Interestingly, a functional relationship exists between CaCC and CFTR (30,31), and Ca 2ϩ -mediated Cl Ϫ secretion is enhanced in cystic fibrosis airways (19). Thus, Ca 2ϩ -activated Cl Ϫ secretion is found in cystic fibrosis but not normal murine nasal epithelium (21).…”

“…p Ͻ 0.05 was accepted as significant. (18,19). ATP induced a negative voltage deflection in Ussing chamber experiments and activated a short circuit current (I sc ) (Fig.…”

Canaux potassiques et physiologie de l’épithélium respiratoire

“…En effet, leur inhibition réduit fortement la sécrétion de Cl -par les cellules des voies aériennes [8,10,19,21]. Inversement, l'activation des canaux KCa3.1, qui stimule la sécrétion de Cl - [19,21], a été proposée comme une stratégie prometteuse pour favoriser le transport de Cl -dans les tissus Fk par des canaux CFTR résiduels ou des canaux Cl -alternatifs ( Figure 3B, Fk).…”