Energetics of Muscle Contraction

Question 1

Metabolic Pathways

o ATP Sinks (3 principal)

Answer 1

§ NaK ATPase
§ SERCA
§ Myosin ATPase

Question 2

ATP sources

Answer 2

Anaerobic alactic reactions
Anaerobic lactic metabolism
§ Aerobic glycolysis

Question 3

Anaerobic alactic reactions

Answer 3

Creatine phosphokinase

Adenylate kinase reaction

Question 4

Comparison of Chemical and Thermomechanical Estimates of Enthalpy Production
o The energy balance sheet
§ Goal is to

Answer 4

balance the enthalpy produced as heat and work during
contraction and to compare this with the amount of energy that can be
explained by chemical reactions

Question 5

Unexplained enthalpy

§ The inference is that unexplained enthalpy components must be due to

Answer 5

unspecified chemical reactions which occur during contraction.
§ Some analysis has led to suggestions that some of the heat produced in
an isometric tetanus is due to the binding of calcium ions to the protein
parvalbumin and, to a lesser extent, troponin

Question 6

Total Heat Production

Answer 6

§ Resting (or Basal)
§ Active Heat Production
Recovery

Question 7

§ Resting (or Basal) Heat Production

Answer 7

• The rate of heat production by passive muscle is appreciable
• The RHP of skeletal muscle contributes ~1/2 total BMR
• Cardiac muscle ~ 5x more than skeletal
• RHP often increased when a muscle is stretched
• Demonstrated that NaK ATPase makes a relatively small
contribution to RHP and nature of other processes involved
remains unclear
• Speculation: May be due to protein synthesis, and in part, to a
proton leakage current across the inner mitochondrial
membrane, and thereby ‘short circuiting’ the chemiosmotic
process of oxidative phosphorylation

Question 8

Initial Heat Production

Answer 8

Appears within a few seconds after a single contraction
at 0 degC, and is followed over the next 20-30 minutes
by recovery heat, the two components being of similar
magnitude
o Attributed to those cellular events associated with
contraction (twitch or tetanus) and relaxation
o Arises from alactic, anaerobic sources

Question 9

Recovery Heat Production

Answer 9

Delayed (reflecting slower kinetics)
o Arises from regeneration of PCr by both anaerobic
(lactic) and aerobic processes

Question 10

Mechanical efficiency

Answer 10

𝜀 = Work/ change in heat + work

total enthaly

Question 11

o Thermodynamics efficiency

Answer 11

𝜂 =Work/ change in Gibbs free energy

Question 12

Shortening Heat

o Shortening heat is defined as

Answer 12

the total amount of heat produced in isotonic
contraction, in excess of that produced in isotonic contraction, in excess of that
produced in the isometric contraction at the same length of the sarcomere

Question 13

The shortening heat is proportional to the __________shortened, with a constant of
proportionality approximately __________ of the speed of shortening
o In all probability, this shortening heat cannot result from a greater rate of crossbridges
turnover since it is not produced by ATP of phosphoryl-creatine
splitting.
o The shortening heat seems to be produced by an extra chemical reaction
occurring in shortening muscle, presumable a noncyclic reaction, whose extent
depends only on the extent of shortening.

Answer 13

distance

independent

Question 14

Initial Heat Production Can be further split into:

Answer 14

Labile Heat
• It is suggested that labile heat may be
attributed to the binding of calcium to
parvalbumin
• We do, however, see a length-dependence
on labile heat, so may in fact be due to
§ Stable Heat
• Due to cross bridges
• Therefore length dependent