Biophys J, July 2000, p. 287-297, Vol. 79, No. 1

A Novel Type of ATP Block on a Ca²⁺-Activated K⁺ Channel from Bullfrog Erythrocytes

Department of Physiology, Osaka Medical College, Takatsuki, Osaka 569-8686, Japan

Using the patch-clamp technique, we have identified an intermediate conductance Ca²⁺-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 Ca²⁺ concentration (K_1/2 = 600 nM) but voltage-independent. These basic characteristics are similar to those of human and frog erythrocyte Ca²⁺-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 ~10 µM ATP (P₀ 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 Mg²⁺, 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.

Biophys J, July 2000, p. 287-297, Vol. 79, No. 1
© 2000 by the Biophysical Society   0006-3495/00/07/287/11  $2.00