S1. Imaging seminar

Question 1

What is the primary role of calcium in cardiac contraction

Answer 1

Triggering muscle contraction by enabling actin-myosin cross-bridge formation

Question 2

How does calcium regulate mitochondrial ATP production

Answer 2

By modulating matrix enzymes like pyruvate and glutamate dehydrogenase

Question 3

What is the significance of minimal ATP reserves in the heart

Answer 3

It emphasizes the need for continuous ATP production by mitochondria

Question 4

What is the function of ‘Rhod-2’ in experiments

Answer 4

To measure cytosolic calcium levels

Question 5

What does ‘MityCam’ specifically measure

Answer 5

Mitochondrial calcium levels

Question 6

What experimental tool quantifies mitochondrial calcium influx

Answer 6

Stopped-flow fluorometry with Rhod-2 and Fura-2

Question 7

Which metabolic substrates enhance calcium-sensitive ATP production

Answer 7

Pyruvate and glutamate

Question 8

What is the role of the mitochondrial calcium uniporter (MCU)

Answer 8

It transports calcium into the mitochondrial matrix

Question 9

What happens to mitochondrial membrane potential (ΔΨm) at high workloads

Answer 9

It is maintained by calcium-sensitive NADH production

Question 10

Why is calcium sensitivity important for mitochondrial ATP production

Answer 10

It allows ATP synthesis to match the workload dynamically

Question 11

What is the unique feature of mammalian ATP synthase compared to bacterial

Answer 11

Higher voltage threshold and non-saturating ATP production curve

Question 12

What is the role of ΔΨm in ATP production

Answer 12

ΔΨm provides the driving force for ATP synthesis by ATP synthase

Question 13

Why is studying mitochondrial calcium signaling challenging

Answer 13

Due to sparse MCU channels and low conductance

Question 14

What is the physiological relevance of ΔΨm maintenance during high workload

Answer 14

Ensures sustained ATP production without ΔΨm collapse

Question 15

Why are MCU channels considered sparse

Answer 15

Only 15-65 channels per mitochondrion in cardiac tissue

Question 16

How does high ADP affect mitochondrial membrane potential

Answer 16

It depolarizes ΔΨm unless calcium is elevated

Question 17

What is the effect of elevated inorganic phosphate on ATP production

Answer 17

It diminishes ATP production at super-physiological levels

Question 18

Why does ATP production depend on ΔΨm

Answer 18

It is driven by proton influx through ATP synthase

Question 19

What is the role of luciferase in ATP production assays

Answer 19

To measure ATP levels via luminescence

Question 20

Why is pyruvate crucial in ATP production experiments

Answer 20

It enables calcium-sensitive ATP production pathways

Question 21

What technique is used to assess ΔΨm quantitatively

Answer 21

Tetramethylrhodamine methyl ester (TMRM) fluorescence

Question 22

Why is ΔΨm critical in cardiovascular health

Answer 22

It supports sustained ATP production for heart function

Question 23

What does MCU dysfunction imply for ATP production

Answer 23

Impaired calcium uptake disrupts NADH generation and ATP synthesis

Question 24

How might altered calcium signaling contribute to heart disease

Answer 24

It can lead to inadequate ATP production under stress conditions

Question 25

What is the unexpected behavior of ATP synthase at high ΔΨm

Answer 25

ATP production exceeds expected rates, suggesting adaptive stoichiometry

Question 26

What is adaptive stoichiometry in ATP synthase

Answer 26

Increased protons per ATP produced at hyperpolarized ΔΨm

Question 27

What is the effect of isoproterenol on calcium dynamics

Answer 27

It elevates both cytosolic and mitochondrial calcium transients

Question 28

Why is studying ΔΨm-voltage curves important

Answer 28

To understand unique characteristics of mammalian ATP synthesis

Question 29

What do simultaneous ADP and calcium experiments reveal

Answer 29

Calcium mitigates ADP-induced ΔΨm depolarization

Question 30

How does ΔΨm behave in isolated mitochondria with no ADP

Answer 30

It remains hyperpolarized at approximately -170 mV

Question 31

How can mitochondrial studies aid heart disease research

Answer 31

By identifying targets to enhance ATP production

Question 32

What do findings about MCU suggest for drug development

Answer 32

Potential for targeting MCU to optimize cardiac energy metabolism

Question 33

What can FRET-based tools measure in mitochondrial studies

Answer 33

Real-time calcium dynamics in cellular compartments

Question 34

What is the relationship between workload and mitochondrial ATP production

Answer 34

ATP production increases with workload due to calcium-sensitive NADH generation

Question 35

What is the role of ATP synthase in mitochondria

Answer 35

It synthesizes ATP using the proton gradient across the inner mitochondrial membrane

Question 36

Why is the mitochondrial calcium uniporter important for cardiac function

Answer 36

It regulates calcium uptake into the mitochondria, crucial for ATP production

Question 37

How do changes in cytosolic calcium affect mitochondrial calcium levels

Answer 37

Cytosolic calcium transients drive calcium influx into mitochondria via the MCU

Question 38

What is the effect of workload on mitochondrial membrane potential

Answer 38

Workload increases the demand for ATP, maintaining ΔΨm through NADH production

Question 39

How does calcium enhance ATP production during increased workload

Answer 39

Calcium activates dehydrogenases that boost NADH production, sustaining ΔΨm

Question 40

What is the significance of studying calcium dynamics in cardiomyocytes

Answer 40

It helps understand energy production and signaling mechanisms critical for heart health