Regulation of K⁺ current in human airway epithelial cells by exogenous and autocrine adenosine

Abstract

The regulatory actions of adenosine on ion channel function are mediated by four distinct membrane receptors. The concentration of adenosine in the vicinity of these receptors is controlled, in part, by inwardly directed nucleoside transport. The purpose of this study was to characterize the effects of adenosine on ion channels in A549 cells and the role of nucleoside transporters in this regulation. Ion replacement and pharmacological studies showed that adenosine and an inhibitor of human equilibrative nucleoside transporter (hENT)-1, nitrobenzylthioinosine, activated K(+) channels, most likely Ca(2+)-dependent intermediate-conductance K(+) (I(K)) channels. A(1) but not A(2) receptor antagonists blocked the effects of adenosine. RT-PCR studies showed that A549 cells expressed mRNA for I(K)-1 channels as well as A(1), A(2A), and A(2B) but not A(3) receptors. Similarly, mRNA for equilibrative (hENT1 and hENT2) but not concentrative (hCNT1, hCNT2, and hCNT3) nucleoside transporters was detected, a result confirmed in functional uptake studies. These studies showed that adenosine controls the function of K(+) channels in A549 cells and that hENTs play a crucial role in this process.

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

“…The intermediateconductance K Ca channel (IK Ca channel), which is sensitive to clotrimazole, Tram34, and charybdotoxin, has been also reported in A459 cells as well as in the trachea and bronchi (12,39,58,60). The detection of IK Ca and Slo1 transcripts in alveolar cells in primary culture reported in our study is consistent with the presence of these two types of K Ca channels in A549 cells.…”

Molecular diversity and function of K+ channels in airway and alveolar epithelial cells

“…We also demonstrated the presence of KCa3.1 in non-CF (NuLi) and CF (CuFi) bronchial cells, although in the latter one, KCa3.1 protein expression and current were reduced compared with NuLi (82). KCa3.1 was also detected in the bronchoalveolar cell line A549 (78), in non-CF and CF nasal polyps (49), 16HBE14oϪ (2) and Calu-3 cells (12). KCa3.1, encoding for intermediate-conductance (ϳ16 pS), KCa channels, sensitive to clotrimazole, charybdotoxin, and TRAM34, is activated by 1-ethyl-2-benzimidazolinone (1-EBIO) and its derivatives.…”

“…KCa3.1, encoding for intermediate-conductance (ϳ16 pS), KCa channels, sensitive to clotrimazole, charybdotoxin, and TRAM34, is activated by 1-ethyl-2-benzimidazolinone (1-EBIO) and its derivatives. Functional evidence of KCa3.1 channels comes from short-circuit current experiments in Ussing chamber with CF and non-CF nasal cells (49), 16HBE14oϪ (2), Calu-3 (12), NHBE (20), NuLi, and CuFi cells (82) and whole cell patchclamp experiments (78). Commonly located at the basolateral membrane of pulmonary epithelia, KCa3.1 currents have also been measured at the apical membrane of bronchial 16HBE14oϪ (2) and NuLi cells (37).…”

The Adenosine Transporter, mENT1, Is a Target for Adenosine Receptor Signaling and Protein Kinase Cϵ in Hypoxic and Pharmacological Preconditioning in the Mouse Cardiomyocyte Cell Line, HL-1

“…However, recent studies suggest a physiologically significant correlation in distribution of certain Ado receptors and ENTs in human neural tissues (Jennings et al, 2001;Bailey et al, 2002). Moreover, ENTs play a role in Ado receptor-dependent regulation of K ϩ channels in epithelial cells (Szkotak et al, 2001). Given the very high expression of ENTs in heart (Pennycooke et al, 2001) and their role in mediating Ado flux across the cell membrane, we believe that ENTs are likely to be an integral, but overlooked, component of Ado physiology in cardiomyocytes.…”