K+ channel openers restore verapamil-inhibited lung fluid resolution and transepithelial ion transport.
BACKGROUND
Lung epithelial Na+ channels (ENaC) are regulated by cell Ca2+ signal, which may contribute to calcium antagonist-induced noncardiogenic lung edema. Although K+ channel modulators regulate ENaC activity in normal lungs, the therapeutical relevance and the underlying mechanisms have not been completely explored. We hypothesized that K+ channel openers may restore calcium channel blocker-inhibited alveolar fluid clearance (AFC) by up-regulating both apical and basolateral ion transport.


METHODS
Verapamil-induced depression of heterologously expressed human alphabetagamma ENaC in Xenopus oocytes, apical and basolateral ion transport in monolayers of human lung epithelial cells (H441), and in vivo alveolar fluid clearance were measured, respectively, using the two-electrode voltage clamp, Ussing chamber, and BSA protein assays. Ca2+ signal in H441 cells was analyzed using Fluo 4AM.


RESULTS
The rate of in vivo AFC was reduced significantly (40.6+/-6.3% of control, P<0.05, n=12) in mice intratracheally administrated verapamil. KCa3.1 (1-EBIO) and KATP (minoxidil) channel openers significantly recovered AFC. In addition to short-circuit current (Isc) in intact H441 monolayers, both apical and basolateral Isc levels were reduced by verapamil in permeabilized monolayers. Moreover, verapamil significantly altered Ca2+ signal evoked by ionomycin in H441 cells. Depletion of cytosolic Ca2+ in alphabetagamma ENaC-expressing oocytes completely abolished verapamil-induced inhibition. Intriguingly, KV (pyrithione-Na), K Ca3.1 (1-EBIO), and KATP (minoxidil) channel openers almost completely restored the verapamil-induced decrease in Isc levels by diversely up-regulating apical and basolateral Na+ and K+ transport pathways.


CONCLUSIONS
Our observations demonstrate that K+ channel openers are capable of rescuing reduced vectorial Na+ transport across lung epithelial cells with impaired Ca2+ signal.
Han
Dong-Yun
DY
Department of Biochemistry, University of Texas Health Science Center at Tyler, Tyler, TX 75708, USA.
Nie
Hong-Guang
HG
Gu
Xiu
X
Nayak
Ramesh C
RC
Su
Xue-Feng
XF
Fu
Jian
J
Chang
Yongchang
Y
Rao
Vijay
V
Ji
Hong-Long
HL
D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000633:toxicity*; D020013:Calcium Signaling / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000819:agonists / Q000378:metabolism; D054086:KATP Channels / Q000819:agonists / Q000378:metabolism; D008168:Lung / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D008914:Minoxidil / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000819:agonists* / Q000378:metabolism; D011654:Pulmonary Edema / Q000139:chemically induced / Q000188:drug therapy* / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013871:Thiones / Q000494:pharmacology*; D014700:Verapamil / Q000633:toxicity*; D014982:Xenopus laevis
D001562:Benzimidazoles; D002121:Calcium Channel Blockers; D053503:Epithelial Sodium Channels; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D054086:KATP Channels; C496925:Kcnn4 protein, mouse; D015221:Potassium Channels; D011725:Pyridines; C507045:SCNN1A protein, human; C507048:SCNN1B protein, human; C507052:SCNN1G protein, human; D013871:Thiones; D008914:Minoxidil; C008704:pyrithione; D012964:Sodium; D014700:Verapamil; C102635:1-ethyl-2-benzimidazolinone; D011188:Potassium; D002118:Calcium