Micromolar concentrations of steroids and of aldosterone antagonists inhibit the outwardly rectifying chloride channel with different kinetics

Abstract

We used the patch-clamp technique to analyse the open/close kinetics of single, outwardly rectifying, intermediate-conductance (ORIC) Cl- channels from cultured epithelial cells under control conditions and in presence of different inhibitors. As observed previously in excised inside/out patches under control conditions, the switching kinetics were characterized by one open-state time constant (tau0 is approximately 30 ms) and three closed-state time constants (tau(cl)is approximately = to 0.2 ms, tau(c2) is approximately = 2 ms and tau(c3) is approximately = 60 ms). Aldosterone, six further steroids and two aldosterone antagonists inhibited channel open probability (NPo) concentration dependently with the potency at 10 micromol/l increasing in the sequence: hydrocortisone, corticosterone, P-oestradiol, cortisone, aldosterone, testosterone, progesterone, canrenone, spironolactone. Although all substances decreased tau(o), neither the steroids nor the aldosterone antagonists affected tau(cl), tau(c2) or tau(c3) or induced additional transitions with additional time constants. Instead, the steroids increased the prevalence of tau(c2) in the dwell-time histograms and the aldosterone antagonists increased the prevalence of tau(c3), both in a concentration-dependent manner. These observations may be explained by a model in which one open state leads to one of three closed states with rate constants alpha, beta and gamma, and in which beta or gamma increase under the influence of steroids or aldosterone antagonists, respectively. Cytosol, which contains a Cl- channel inhibitor of unknown molecular structure, (Krick et al., Pflügers Arch 418:491, 1991) was also tested, but the results did not conform to the blocker mechanisms described above. This shows that there are even further modes of channel inhibition and argues against the cytosolic Cl- channel inhibitor being a steroid.

An outwardly rectifying anion channel in human leukaemic K562 cells

“…The channels described in this research were highly selective for Cl -over Na + and had a conductance consistent with previous reports on ORCC [12,14,20]. Gluconate currents and E r were observed when most of the internal Cl -ions had been replaced by gluconate, although the gluconate/Cl permeability ratio for these channels was very low under bionic conditions.…”

“…ORCC channels can be observed after application of a brief depolarizing [19] or hyperpolarizing [20] pulses. The channel is characterized by a disparity between the amplitudes of inwards and outwards unitary current in symmetrical solution.…”

“…We assessed the effect of glibenclamide [20,21,22]. The drug, added to the cytoplasmic side of the patch reduced the activity at all potentials.…”

Rapid, non-genomic actions of progesterone and estradiol on steady-state calcium and resting calcium influx in lens epithelial cells

“…Electrophysiological evidence for an action of steroids on ion channels is accumulating for a variety of cell systems and a variety of channel types including ligand-gated receptors (e.g. acetylcholine receptors) [1,4], inwardly rectifying K + channels [9,29], outwardly rectifying intermediate conductance Cl -channels (ORIC) [31], epithelial Na + channels [35], and smooth muscle L-type Ca 2+ channels [7]. Since there is currently no evidence to indicate steroid-induced increases in those ionic conductances that typically mediate resting Ca 2+ influx (e.g., non-selective cation channels, Ca 2+ leakage channels), it is quite possible that the increases in resting Ca 2+ influx induced by progesterone (Fig.…”

Voltage‐dependent K+ channel acts as sex steroid sensor in endocrine cells of the human ovary

“…Clearly, in other organs, ion channels (e.g., inwardrectifying K þ channel, L-type Ca 2þ channel) were found to be steroid-sensitive (Steidl et al, 1991;Nakajima et al, 1995;Singleton et al, 1999;Okabe et al, 2000;Rabe and Frömter, 2000;Kelly and Levin, 2001;Henriquez and Riquelme, 2002;Von Ledebur et al, 2002;Oliver et al, 2004). A well studied example is the BK Ca channel, for which both opening and blocking were reported (White et al, 1995;Valverde et al, 1999;Li and Hay, 2000;Chiang and Wu, 2001;Deenadayalu et al, 2001;Dick et al, 2001;Clarke et al, 2002).…”