Phosphoinositides decrease ATP sensitivity of the cardiac ATP-sensitive K+ channel: A molecular probe for the mechanism of ATP-sensitive inhibition

Zheng Fan, Jonathan C. Makielski

Research output: Contribution to journalArticle

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Abstract

Anionic phospholipids modulate the activity of inwardly rectifying potassium channels (Fan, Z., and J.C. Makielski. 1997. J. Biol. Chem. 272:5388-5395). The effect of phosphoinositides on adenosine triphosphate (ATP) inhibition of ATP-sensitive potassium channel (K(ATP)) currents was investigated using the inside-out patch clamp technique in cardiac myocytes and in COS-1 cells in which the cardiac isoform of the sulfonylurea receptor, SUR2, was coexpressed with the inwardly rectifying channel Kir6.2. Phosphoinositides (1 mg/ml) increased the open probability of KATe in low [ATP] (1 μM) within 30 s. Phosphoinositides desensitized ATP inhibition with a longer onset period (>3 min), activating channels inhibited by ATP (1 mM). Phosphoinositides treatment for 10 min shifted the half-inhibitory [ATP] (K(i)) from 35 μM to 16 mM. At the single-channel level, increased [ATP] caused a shorter mean open time and a longer mean closed time. Phosphoinositides prolonged the mean open time, shortened the mean closed time, and weakened the [ATP] dependence of these parameters resulting in a higher open probability at any given [ATP]. The apparent rate constants for ATP binding were estimated to be 0.8 and 0.02 mM-1 ms-1 before and after 5-min treatment with phosphoinositides, which corresponds to a K(i) of 35 μM and 5.8 mM, respectively. Phosphoinositides failed to desensitize adenosine inhibition of K(ATP). In the presence of SUR2, phosphoinositides attenuated MgATP antagonism of ATP inhibition. Kir6.2ΔC35, a truncated Kir6.2 that functions without SUR2, also exhibited phosphoinositide desensitization of ATP inhibition. These data suggest that (a) phosphoinositides strongly compete with ATP at a binding site residing on Kir6.2; (b) electrostatic interaction is a characteristic property of this competition; and (c) in conjunction with SUR2, phosphoinositides render additional, complex effects on ATP inhibition. We propose a model of the ATP binding site involving positively charged residues on the COOH-terminus of Kir6.2, with which phosphoinositides interact to desensitize ATP inhibition.

Original languageEnglish (US)
Pages (from-to)251-269
Number of pages19
JournalJournal of General Physiology
Volume114
Issue number2
DOIs
StatePublished - Aug 1 1999

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Molecular Probes
Phosphatidylinositols
Adenosine Triphosphate
Binding Sites
Sulfonylurea Receptors
Inwardly Rectifying Potassium Channel

All Science Journal Classification (ASJC) codes

  • Physiology

Cite this

Phosphoinositides decrease ATP sensitivity of the cardiac ATP-sensitive K+ channel : A molecular probe for the mechanism of ATP-sensitive inhibition. / Fan, Zheng; Makielski, Jonathan C.

In: Journal of General Physiology, Vol. 114, No. 2, 01.08.1999, p. 251-269.

Research output: Contribution to journalArticle

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