A novel type of ATP block on a Ca(2+)-activated K(+) channel from bullfrog erythrocytes

• Published in: Biophysical journal Vol. 79; no. 1; pp. 287 - 297
• Main Authors: Shindo, M, Imai, Y, Sohma, Y
• Format: Journal Article
• Language: English
• Published: United States 01-07-2000
• Subjects: Adenosine Diphosphate - pharmacology; Adenosine Monophosphate - pharmacology; Adenosine Triphosphate - metabolism; Adenosine Triphosphate - pharmacology; Adenylyl Imidodiphosphate - pharmacology; Animals; Calcium - metabolism; Calcium - pharmacology; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Dose-Response Relationship, Drug; Enzyme Inhibitors - pharmacology; Erythrocytes - cytology; Erythrocytes - drug effects; Erythrocytes - metabolism; Hypoglycemic Agents - pharmacology; In Vitro Techniques; Magnesium - pharmacology; Membrane Potentials - drug effects; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels - metabolism; Protein Kinase C - antagonists & inhibitors; Rana catesbeiana
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(00)76291-6

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.