A disrupter of actin microfilaments impairs sulfonylurea-inhibitory gating of cardiac KATP channels

Abstract

The efficacy with which sulfonylurea drugs inhibit cardiac ATP-sensitive K+ (KATP) channels is reduced during metabolic compromise and cellular contracture. Disruption of the actin microfilament network, which occurs under similar conditions, reduces the sensitivity of the channel toward intracellular ATP. To investigate whether a disrupter of actin microfilaments could also affect the responsiveness of the KATP channel to sulfonylurea drugs, single-channel currents were measured in the inside-out configuration of excised patches from guinea pig ventricular myocytes. Treatment of the internal side of patches with deoxyribonuclease (DNase) I (100 micrograms/ml), which forms complexes with G actin and prevents actin filament formation, antagonized sulfonylurea-induced inhibition of KATP channels that was coupled with a loss of sensitivity to ATP. The apparent dissociation constant and Hill coefficient for the inhibitory effect of glyburide, a prototype sulfonylurea, on KATP-channel opening were, respectively, 0.13 microM and 0.95 before and 2.7 microM and 0.98 after DNase treatment. DNase did not alter intraburst kinetic properties of the channel. When DNase was denatured or coincubated with purified actin (200 micrograms/ml), it no longer decreased glyburide-induced channel inhibition. This suggests that sulfonylurea-inhibitory gating of cardiac KATP channels may also be regulated through a mechanism involving subsarcolemmal actin microfilament networks.

Dual role of K ATP channel C-terminal motif in membrane targeting and metabolic regulation

“…For well over a decade, the ion channel field has struggled to identify the molecular link between the K ATP channel and the cytoskeleton (24)(25)(26). The presence of an adapter complex was first proposed in the mid 1990's, based on a series of experiments that demonstrated a striking stimulatory effect of actin filament disrupting agents on K ATP channel opening (25).…”

“…The presence of an adapter complex was first proposed in the mid 1990's, based on a series of experiments that demonstrated a striking stimulatory effect of actin filament disrupting agents on K ATP channel opening (25). Specifically, disruption of the actin cytoskeleton has been shown to activate K ATP channel activity in excitable cells by reducing the sensitivity of K ATP channels to ATP-dependent channel closure (24)(25)(26). Thus, impairment in ATP sensitivity indicates a transduction pathway of inhibitory gating signals determined by the integrity of the submembrane cytoskeletal network.…”

Ketogenic Diet Metabolites Reduce Firing in Central Neurons by Opening KATPChannels

“…There are precedents for such a loss of sulfonylurea sensitivity. Sulfonylurea sensitivity of K ATP channels can vary greatly between different cells expressing identical Kir6 and SUR subtypes and can vary with physiological changes in negatively charged lipids (Koster et al, 1999;Krauter et al, 2001), metabolic stress (Findlay, 1993), reactive oxygen species (Krippeit-Drews et al, 1999), intracellular Ca 2ϩ (Koriyama et al, 2001), cytoskeletal disruption (Brady et al, 1996), or nucleotide levels (Brady et al, 1998). Ketone bodies could alter one of these parameters (in parallel with ATP production) to produce blocker insensitivity.…”

ATP-sensitive K channel channel/enzyme multimer: Metabolic gating in the heart

“…There are several contributors including physical interactions between the channel and the actin cytoskeleton [95][96][97][98][99], as well as additional metabolic systems such as lactate dehydrogenase (LDH) that, like CK and AK has also been shown to physical associate with K ATP channel proteins [8,91,100]. LDH catalyzes the reaction NADH + pyruvate ↔ lactate + NAD.…”