A novel type of ATP block on a Ca(2+)-activated K(+) channel from bullfrog erythrocytes.
Using the patch-clamp technique, we have identified an intermediate conductance Ca(2+)-activated K(+) channel from bullfrog (Rana catesbeiana) erythrocytes and have investigated the regulation of channel activity by cytosolic ATP. The channel was highly selective for K(+) over Na(+), gave a linear I-V relationship with symmetrical 117.5 mM K(+) solutions and had a single-channel conductance of 60 pS. Channel activity was dependent on Ca(2+) concentration (K(1/2) = 600 nM) but voltage-independent. These basic characteristics are similar to those of human and frog erythrocyte Ca(2+)-activated K(+) (Gardos) channels previously reported. However, cytoplasmic application of ATP reduced channel activity with block exhibiting a novel bell-shaped concentration dependence. The channel was inhibited most by approximately 10 microM ATP (P(0) reduced to 5% of control) but less blocked by lower and higher concentrations of ATP. Moreover, the novel type of ATP block did not require Mg(2+), was independent of PKA or PKC, and was mimicked by a nonhydrolyzable ATP analog, AMP-PNP. This suggests that ATP exerts its effect by direct binding to sites on the channel or associated regulatory proteins, but not by phosphorylation of either of these components.
Shindo
M
M
Department of Physiology, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan.
Imai
Y
Y
Sohma
Y
Y
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004912:Erythrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011892:Rana catesbeiana
D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000266:Adenylyl Imidodiphosphate; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D008274:Magnesium; D002118:Calcium