Maxi K+ channels in the basolateral membrane of the exocrine frog skin gland regulated by intracellular calcium and pH.
With the single-channel patch-clamp technique we have identified Ca2+-sensitive, high-conductance (maxi) K+ channels in the basolateral membrane (BLM) of exocrine gland cells in frog skin. Under resting conditions, maxi K+ channels were normally quiescent, but they were activated by muscarinic agonists or by high serosal K+. In excised inside-out patches and with symmetrical 140mmol/l K+, single-channel conductance was 200pS and the channel exhibited a high selectivity for K+ over Na+. Depolarization of the BLM increased maxi K+ channel activity. Increasing cytosolic free Ca2+ (by addition of 100nmol/l thapsigargin to the bathing solution of cell-attached patches also increased channel activity, whereas thapsigargin had no effect when added to excised inside-out patches. An increase in cytosolic free Ca2+ directly activated channel activity in a voltage-dependent manner. Maxi K+ channel activity was sensitive to changes in intracellular pH, with maximal activity at pH 7.4 and decreasing activities following acidification and alkalinization. Maxi K+ channel outward current was reversibly blocked by micromolar concentrations of Ba2+ from the cytosolic and extracellular site, and was irreversibly blocked by micromolar concentrations of charybdotoxin and kaliotoxin from the extracellular site in outside-out patches.
Andersen
H K
HK
Zoophysiological Laboratory, August Krogh Institute, Universitetsparken 13, DK 2100 Copenhagen, Denmark.
Urbach
V
V
Van Kerkhove
E
E
Prosser
E
E
Harvey
B J
BJ
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005088:Exocrine Glands / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011893:Rana esculenta; D012867:Skin / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D013729:Terpenes; D001464:Barium; D019284:Thapsigargin; D002118:Calcium