Members of the TMEM16 (Anoctamin) family of membrane proteins have been shown to be essential constituents of the Ca2+-activated Cl− channel (CaCC) in many cell types. In this study, we have investigated the electrophysiological properties of mouse TMEM16F. Heterologous expression of TMEM16F in HEK293 cells resulted in plasma membrane localization and an outwardly rectifying ICl,Ca that was activated with a delay of several minutes. Furthermore, a significant Na+ current was activated, and the two permeabilities were correlated according to PNa = 0.3 PCl. The current showed an EC50 of 100 µM intracellular free Ca2+ concentration and an Eisenman type 1 anion selectivity sequence of PSCN > PI > PBr > PCl > PAsp. The mTMEM16F-associated ICl,Ca was abolished in one mutant of the putative pore region (R592E) but retained in two other mutants (K616E and R636E). The mutant K616E had a lower relative permeability to iodide, and the mutant R636E had an altered anion selectivity sequence (PSCN = PI = PBr = PCl > PAsp). Our data provide evidence that TMEM16F constitutes a Ca2+-activated anion channel or a pore-forming subunit of an anion channel with properties distinct from TMEM16A.

Anoctamin 6 (ANO6), also known as TMEM16F, has been shown to be a calcium-activated anion channel with delayed calcium activation. The cellular function of ANO6 is under debate, and different groups have come to different conclusions about ANO6’s physiological role. Although it is now quite well established that ANO6 is distinct from the volume-regulated anion channel, it is still unclear whether ANO6 or other anoctamins can be activated by cell swelling. In this study, we suggest that ANO1, ANO6, and ANO10 do not contribute to the volume-activated current in ANO-overexpressing HEK293 cells. Furthermore, knock-down of ANO6 in Ehrlich ascites tumor cells (EATC) and Ehrlich–Lettre ascites (ELA) did not decrease but instead significantly increased swelling-activated membrane currents. Knock-down of ANO6 in EATC did not reduce regulatory volume decrease (RVD) in the absence of extracellular calcium, whereas it significantly reduced RVD in the presence of calcium. Interestingly, we found that knock-down of ANO6 in ELA cells resulted in a decrease in cisplatin-induced caspase-3 activity, confirming earlier findings that ANO6 is involved in apoptosis. Finally, knock-down of ANO1 and ANO6 did not affect the volume-sensitive release of taurine in ELA cells. Thus, our data provide evidence that ANO6 cannot be activated directly by cell swelling unless Ca2+ is present. We also conclude that ANO6 carries a current during RVD, provided extracellular calcium is present. Thus, swelling activation of ANO6 requires the presence of free calcium.

59 patients with obstructive prostatic hypertrophy (BPH) were evaluated regarding the influence of prostatectomy on upper urinary tract function by means of [51Cr]EDTA clearance and gamma camera renography measurements. 25 patients were randomly allocated to transvesical and 34 patients to transurethral prostatectomy. At the 6-month follow-up a slight decrease in glomerular filtration rate (GFR) was seen in the total patient group. Residual renal activity 20 min following injection (A20) as well as half-peak time values showed upper urinary tract obstruction in 54% of the patients preoperatively, whereas dilatation of the upper urinary tract was demonstrated at i.v. pyelography in only 15%. Patients with renographic obstruction preoperatively had low GFR values compared with patients without obstruction. In patients with upper urinary tract obstruction, prostatectomy relieved the obstruction, even in the case of normal urography. In patients with normal upper urinary tract, a clinically insignificant decrease in GFR and increase in A20 and half-peak time was observed. No differences with regard to upper urinary tract function were seen on comparing transurethral with transvesical prostatectomy.