Specific CFTR mutations confer residual CFTR function to rectal epithelia, which is related closely to a mild disease phenotype. Quantification of rectal CFTR-mediated Cl- secretion may be a sensitive test to predict the prognosis of CF disease and identify CF patients who would benefit from therapeutic strategies that would increase residual CFTR activity.

The acid-and volume-sensitive TASK2 K ؉ channel is strongly expressed in renal proximal tubules and papillary collecting ducts. This study was aimed at investigating the role of TASK2 in renal bicarbonate reabsorption by using the task2 ؊͞؊ mouse as a model. After backcross to C57BL6, task2 ؊͞؊ mice showed an increased perinatal mortality and, in adulthood, a reduced body weight and arterial blood pressure. Patch-clamp experiments on proximal tubular cells indicated that TASK2 was activated during HCO 3 ؊ transport. In control inulin clearance measurements, task2 ؊͞؊ mice showed normal NaCl and water excretion. During i.v. NaHCO3 perfusion, however, renal Na ؉ and water reabsorption capacity was reduced in ؊͞؊ animals. In conscious task2 ؊͞؊ mice, blood pH, HCO 3 ؊ concentration, and systemic base excess were reduced but urinary pH and HCO 3 ؊ were increased. These data suggest that task2 ؊͞؊ mice exhibit metabolic acidosis caused by renal loss of HCO 3 ؊ . Both in vitro and in vivo results demonstrate the specific coupling of TASK2 activity to HCO 3 ؊ transport through external alkalinization. The consequences of the task2 gene inactivation in mice are reminiscent of the clinical manifestations seen in human proximal renal tubular acidosis syndrome.

Using equivalent short circuit current (ISC) measurements we examined the effect of extracellular ATP on transepithelial ion transport in M‐1 mouse cortical collecting duct cells. Apical addition of ATP produced a rapid transient peak increase in ISC. This was followed by a fall below basal ISC due to a reduction in the amiloride‐sensitive ISC component. The ATP‐induced ISC increase was preserved in the presence of apical amiloride while it was reduced in the absence of extracellular Cl− and in the presence of the apical Cl− channel blockers diphenylamine‐2‐carboxylic acid (DPC, 1 mM), DIDS (300 μM) and niflumic acid (100 μM). The stimulatory effect of apical ATP on ISC was concentration dependent with an EC50 of about 0.6 μM. Basolateral ATP elicited a similar ISC response. Experiments using the ATP scavenger hexokinase demonstrated that the ATP effects were elicited via separate apical and basolateral receptors. ATP and UTP applied to either the apical or the basolateral bath equi‐potently stimulated ISC while ‘purified’ ADP and UDP had no effect consistent with P2Y2 purinoceptors, the expression of which was confirmed using RT‐PCR. Intracellular calcium concentration ([Ca2+]i) measurements using fura‐2 demonstrated that ATP and UTP elicited a rise in [Ca2+]i with EC50 values of 1.1 and 0.6 μM, respectively. The shape and time course of the calcium response were similar to those of the ISC response. The peak ISC response was preserved in the nominal absence of extracellular calcium but was significantly reduced in cells pre‐incubated with the calcium chelator BAPTA AM. We conclude that in M‐1 cells extracellular ATP reduces amiloride‐sensitive Na+ absorption and stimulates Cl− secretion via calcium‐activated Cl− channels through activation of P2Y2 purinoreceptors located in the apical and basolateral membrane.

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.

Posttreatment sulfide infusion after blunt chest trauma did not affect the impaired lung mechanics and gas exchange but attenuated stress protein expression and apoptotic cell death. This protective effect was amplified by moderate hypothermia. The simultaneous reduction in cystathionine-β synthase and cystathionine-γ lyase expression supports the role of H2S-generating enzymes as an adaptive response during stress states.