Mitochondrial potassium

transport: the role of the

MitoKATP

Mitochondrial potassium

transport: the role of the

MitoKATP

WeiGuo

2005.1.14

WeiGuo

2005.1.14

Mitochondrial potassium cycle Mitochondrial potassium cycle

• Mitochondria are structurally complex. The inner

membrane contains the essential components of

the electron transport proteins and all of the

exchange carriers

• Mitochondria are structurally complex. The inner

membrane contains the essential components of

the electron transport proteins and all of the

exchange carriers

Mitochondrial potassium cycleMitochondrial potassium cycle

• The mitochondrial K+ cycle consists of influx and

efflux pathways for K+, H+, and anions

• These ions are exchanged between the matrix and

the intermembrane space ( IMS ); however, the

outer membrane (OM) does not present a barrier

to further exchange of small ions with the cytosol

• The mitochondrial K+ cycle consists of influx and

efflux pathways for K+, H+, and anions

• These ions are exchanged between the matrix and

the intermembrane space ( IMS ); however, the

outer membrane (OM) does not present a barrier

to further exchange of small ions with the cytosol

Influx pathway for potassiumInflux pathway for potassium

IMS

matrix

MitoKAT

P

K+

leak

K+ K+

H+

ETS

∆Ψ

Matrix alkalinizatio

n

Pi-

OH-

Pi-H+ symporte

r

Electron transport system (ETS) generates membrane potential (∆Ψ). ∆Ψ can drive K+ influx by diffusion (‘‘K+ leak’’) and via the mitoKATP. This K+ for H+ exchange will alkalinize the matrix, causing phosphate to enter via the Pi-H+ symporter.

Efflux pathway for potassiumEfflux pathway for potassium

• Net uptake of K+ salts will be accompanied by

osmotically obligated water, resulting in matrix

swelling. Excess matrix K+ is then ejected by the

K+/H+ antiporter

• Net uptake of K+ salts will be accompanied by

osmotically obligated water, resulting in matrix

swelling. Excess matrix K+ is then ejected by the

K+/H+ antiporter

K+-H+

antiporter

Early work on the potassium cycleEarly work on the potassium cycle

• Diffusive K+ influx would be sufficient to cause

matrix water content to increase, with eventual

lysis. This would be avoided by the K+/H+

antiporter

• Diffusive K+ influx would be sufficient to cause

matrix water content to increase, with eventual

lysis. This would be avoided by the K+/H+

antiporter

synthesizing ATP at very high rates

∆Ψ decreases matrix contraction

mito-KATP

Maintain matrix volume

MitoKATP meets a different need in

volume regulation

MitoKATP on matrix and IMS volumes MitoKATP on matrix and IMS volumes

• MitoKATP opening was shown to regulate matrix

volume during ischemia and state 3 respiration

• MitoKATP opening was shown to regulate matrix

volume during ischemia and state 3 respiration

Addition of antimycin A to simulate ischemia

DE

depolarization and decrease in

diffusive K+ influxaddition of ADP to trigger state 3 respiration

10–15% contraction in matrix volume

matrix volume return to original state

5-HD

MitoKATP on matrix and IMS volumesMitoKATP on matrix and IMS volumes

• Changes in IMS could be estimated by means of

membrane surface areas (SA)

• Studies shown that mitoKATP opening decreases

IMS volume

• Physiological changes in matrix volume may have

important effects on IMS structure–function

• Changes in IMS could be estimated by means of

membrane surface areas (SA)

• Studies shown that mitoKATP opening decreases

IMS volume

• Physiological changes in matrix volume may have

important effects on IMS structure–function

Two distinct consequences of opening mitoKATP Two distinct consequences of opening mitoKATP

• When ∆Ψ is high → opening mitoKATP → matrix

alkalinization → production of reactive oxygen

species (ROS) ↑

• When ∆Ψ is depressed → opening mitoKATP →

prevent contraction of the matrix and expansion of

the IMS

• When ∆Ψ is high → opening mitoKATP → matrix

alkalinization → production of reactive oxygen

species (ROS) ↑

• When ∆Ψ is depressed → opening mitoKATP →

prevent contraction of the matrix and expansion of

the IMS

Is mitoKATP involved in all modes of cardioprotection ?Is mitoKATP involved in all modes of cardioprotection ?

• Ischemic preconditioning √

• Calcium preconditioning √

• KCO preconditioning √

• Delayed preconditioning √

• Adaptive preconditioning √

• Na+/H+ exchange inhibition √

• Ischemic post-conditioning ?

• Ischemic preconditioning √

• Calcium preconditioning √

• KCO preconditioning √

• Delayed preconditioning √

• Adaptive preconditioning √

• Na+/H+ exchange inhibition √

• Ischemic post-conditioning ?

During which phase is mitoKATP opening crucial for cardioprotection?

During which phase is mitoKATP opening crucial for cardioprotection?

• MitoKATP is proposed to play distinct roles in

each phase of ischemia– reperfusion

• MitoKATP is proposed to play distinct roles in

each phase of ischemia– reperfusion

Preconditioning

phase

Ischemic

phase

Reperfusion

phase

As a end-effector

of cardioprotection

As a end-effector

of cardioprotection

As a trigger of

cardioprotection

During the preconditioning phaseDuring the preconditioning phase

• The role of mitoKATP opening is to increase

production of ROS

• Moderate increases in ROS play an important

second messenger role in a variety of signaling

pathways

• The role of mitoKATP opening is to increase

production of ROS

• Moderate increases in ROS play an important

second messenger role in a variety of signaling

pathways

A proposed mechanism for increased ROSA proposed mechanism for increased ROS

ROS↑

IMS

Matrix

Matrix alkalinizatio

n

OH-

Pi-H+ symporte

r Pi-K+ K+

MitoKATP K+

leak

Pi- uptake will be less than K+ uptake

K+ uptake creating a gradient for uptake of Pi on the Pi–H+ symporter, Pi uptake will be less than K+ uptake, because Pi is present in much lower concentrations than K+. For this reason, matrix pH always increases when matrix volume increases due to uptake of K+ and Pi.

During the ischemic phaseDuring the ischemic phase

• mitochondrial permeability transition (MPT)

• The primary role of matrix Ca2 + is to stimulate ROS

production upon reperfusion

• Ca2 + cannot open MPT unless ROS are present

• Cytosolic Ca2 + may play an additional role in

promoting ROS oxidation of adenine nucleotide

translocase (ANT)

• mitochondrial permeability transition (MPT)

• The primary role of matrix Ca2 + is to stimulate ROS

production upon reperfusion

• Ca2 + cannot open MPT unless ROS are present

• Cytosolic Ca2 + may play an additional role in

promoting ROS oxidation of adenine nucleotide

translocase (ANT)

The mechanism by which mitoKATP

protects the heart during ischemia phase

The mechanism by which mitoKATP

protects the heart during ischemia phase

• The opening of mitoKATP preserves the structure–

function of the IMS and maintains the low

permeability of the outer membrane to adenine

nucleotides, thereby preserving ADP for

phosphorylation upon reperfusion

• The opening of mitoKATP preserves the structure–

function of the IMS and maintains the low

permeability of the outer membrane to adenine

nucleotides, thereby preserving ADP for

phosphorylation upon reperfusion

Outer mitochondrial membrane permeability to

ADP and ATP was controlled by voltage-dependent

anion channel (VDAC)

• In heart, VDAC is normally in a low-conductance state that is poorly permeable to nucleotides, and energy transfers are mediated instead by creatine and creatine phosphate.

matrix

IMS

Outer Mem

Inner Mem

ATP

ADP

ANT

VDAC

CKCr / PCr

•During ischemia, ∆Ψ will decrease, resulting in reduced uptake of K+,contraction of the matrix, and expansion of the IMS

MitoKATP regulation of VDAC permeability to

nucleotides during ischemia

•This means that all of cellular ATP is available for hydrolysis, and, ultimately, unavailability of ADP for rephosphorylation upon reperfusion

•IMS expansion will cause Mi-CK to dissociate from VDAC, leading to a high outer membrane conductance to ATP and ADP

During the reperfusion phase During the reperfusion phase

• The opening of mitoKATP facilitates rapid energy

conversion to phosphocreatine (PCr) . Under

these conditions, mitochondria will not produce a

burst of ROS upon reperfusion, and the

irreversible opening of the MPT will not occur

• The opening of mitoKATP facilitates rapid energy

conversion to phosphocreatine (PCr) . Under

these conditions, mitochondria will not produce a

burst of ROS upon reperfusion, and the

irreversible opening of the MPT will not occur

Outer Mem

Inner Mem

ATP / ADP

ANT

VDAC

CK

Energy transfer from mitochondria to myofibrils is

mediated by two parallel

pathways—creatine/creatine phosphate (Cr/CrP)

and ATP/ADP

• In the Cr/CrP system, myofibrillar creatine kinase converts ADP to creatine. Mi-CK bridge the IMS between outer membrane VDAC and inner membrane ANT.

Cr / PCr

• Cr/CrP is more efficient

•About 67% of the energy production in heart has been found to arise from the CK system

• During reperfusion, expansion of the IMS will cause Mi-CK to dissociate from VDAC, leading to a high outer membrane conductance to ATP and ADP

MitoKATP facilitates rapid energy conversion to

phosphocreatine (PCr) during the reperfusion

phase

• If mitoKATP is open, the outer membrane will retain its low permeability to nucleotides, and the mitochondria can restore energy levels using the more efficient metabolic channeling via Mi-CK

SummarySummary

• Mitochondria potassium cycle

• Two distinct consequences of Opening mitoKATP

• mitoKATP plays cardio-protective effect during all

three phases of the ischemia–reperfusion injury

• Mitochondria potassium cycle

• Two distinct consequences of Opening mitoKATP

• mitoKATP plays cardio-protective effect during all

three phases of the ischemia–reperfusion injury

Thank you !