The basolateral Ca2+-dependent K+ channel in rat colonic crypt cells.
Previous studies have indicated that a 16-pS K+ channel (KCca) in the basolateral membrane is responsible for the acetylcholine-induced whole-cell K+ conductance in these cells. In the present study we have examined this channel in excised inside-out patches of the basolateral membrane. Over a wide voltage range this channel showed inward rectification. The Ca2+ sensitivity was very marked, with a Hill coefficient of three and with half-maximal activation at 330 nmol/l. After several minutes most channels showed a slow run-down. Channel activity could be refreshed by addition of ATP (1 mmol/l) to the bath solution. The non-metabolizable derivative 5'-adenylylimidodiphosphate (AMP-PNP) had no such effect. In contrast, it inhibited channel activity by some 50%. ATP and its derivatives had no effect on the Ca2+ sensitivity. Channels activated by ATP were subsequently studied in the presence of alkaline (10 kU/l) or acidic (1 kU/l) phosphatase. Both phosphatases reduced channel activity significantly. These data suggest that the 16-pS K+ channel is directly controlled by cytosolic Ca2+. This regulatory step is probably distal to an activation produced by protein-kinase-C-dependent phosphorylation. As is the case for several other K+ channels, high concentrations of non-metabolizable ATP analogues inhibit this channel.
Nielsen
M S
MS
Physiologisches Institut, Albert-Ludwigs-Universität, Hermann-Herder-Strasse 7, D-79104 Freiburg, Germany.
Warth
R
R
Bleich
M
M
Weyand
B
B
Greger
R
R
D000135:Acid Phosphatase / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000469:Alkaline Phosphatase / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000502:physiology; D003106:Colon / Q000502:physiology* / Q000648:ultrastructure; D004553:Electric Conductivity; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D015221:Potassium Channels; D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate; D000469:Alkaline Phosphatase; D000135:Acid Phosphatase; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium