Evans Blue is not a suitable inhibitor of the epithelial sodium channel δ-subunit

The subunit of epithelial sodium channel in humans-a potential player in vascular physiology

Vascular epithelial sodium channels (ENaCs) made up of canonical α, β, and γ subunits have attracted more attention recently owing to their physiological role in vascular health and disease. A fourth subunit, δ-ENaC, is expressed in various mammalian species, except mice and rats, which are common animal models for cardiovascular research. Accordingly, δ-ENaC is the least understood subunit. However, the recent discovery of δ subunit in human vascular cells indicates that this subunit may play a significant role in normal/pathological vascular physiology in humans. Channels containing the δ subunit have different biophysical and pharmacological properties compared with channels containing the α subunit, with the potential to alter the vascular function of ENaC in health and disease. Hence, it is important to investigate the expression and function of δ-ENaC in the vasculature to identify whether δ-ENaC is a potential new drug target for the treatment of cardiovascular disease. In this review, we will focus on the existing knowledge of δ-ENaC and implications for vascular physiology and pathophysiology in humans.

Hydrogen sulfide stimulates CFTR in Xenopus oocytes by activation of the cAMP/PKA signalling axis

Hydrogen sulfide (H₂S) has been recognized as a signalling molecule which affects the activity of ion channels and transporters in epithelial cells. The cystic fibrosis transmembrane conductance regulator (CFTR) is an epithelial anion channel and a key regulator of electrolyte and fluid homeostasis. In this study, we investigated the regulation of CFTR by H₂S. Human CFTR was heterologously expressed in Xenopus oocytes and its activity was electrophysiologically measured by microelectrode recordings. The H₂S-forming sulphur salt Na₂S as well as the slow-releasing H₂S-liberating compound GYY4137 increased transmembrane currents of CFTR-expressing oocytes. Na₂S had no effect on native, non-injected oocytes. The effect of Na₂S was blocked by the CFTR inhibitor CFTR_inh172, the adenylyl cyclase inhibitor MDL 12330A, and the protein kinase A antagonist cAMPS-Rp. Na₂S potentiated CFTR stimulation by forskolin, but not that by IBMX. Na₂S enhanced CFTR stimulation by membrane-permeable 8Br-cAMP under inhibition of adenylyl cyclase-mediated cAMP production by MDL 12330A. These data indicate that H₂S activates CFTR in Xenopus oocytes by inhibiting phosphodiesterase activity and subsequent stimulation of CFTR by cAMP-dependent protein kinase A. In epithelia, an increased CFTR activity may correspond to a pro-secretory response to H₂S which may be endogenously produced by the epithelium or H₂S-generating microflora.