Micromolar concentrations of steroids and of aldosterone antagonists inhibit the outwardly rectifying chloride channel with different kinetics.
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.
Rabe
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A
Institut für Nieren-und Membranphysiologie der J.W. Goethe-Universität, Frankfurt/Main, Germany.
Frömter
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D000450:Aldosterone / Q000494:pharmacology*; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D002192:Canrenone / Q000494:pharmacology; D018118:Chloride Channels / Q000737:chemistry / Q000502:physiology*; D003345:Corticosterone / Q000494:pharmacology; D003600:Cytosol / Q000737:chemistry / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology; D019073:HT29 Cells; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D008055:Lipids / Q000737:chemistry; D000451:Mineralocorticoid Receptor Antagonists / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011374:Progesterone / Q000494:pharmacology; D013148:Spironolactone / Q000494:pharmacology*; D013739:Testosterone / Q000494:pharmacology
D000893:Anti-Inflammatory Agents; D018118:Chloride Channels; D008055:Lipids; D000451:Mineralocorticoid Receptor Antagonists; D013148:Spironolactone; D013739:Testosterone; D000450:Aldosterone; D011374:Progesterone; D004958:Estradiol; D002192:Canrenone; D003345:Corticosterone; D006854:Hydrocortisone