The concentration of troponin C, TnC (the Ca 2+ binding proteins of the thin fil

Question

The concentration of troponin C, TnC (the Ca2+ binding proteins of the thin filament) in heart muscle cells is estimated at about 70 nmol/g wet weight of tissue. O2 consumption is estimated to be about 0.09 mL O2 per min per g wet weight of tissue. Assume the TnC is 60% saturated during normal, resting contractions. Assume that 80% of the activating Ca2+ originates from SR stores. Assume a heart rate of 70/min. Assume free energy of ATP hydrolysis is 57 kJ/mol and that metabolism obtains 20.3 kJ/L O2 consumed.

A. How much Ca2+ is released and taken back up per heartbeat, per g of tissue?

B: How much energy is consumed to take Ca2+ back up into the SR, per heartbeat?

C: What fraction of the cell’s energy consumption is used for this purpose?

D: How much Ca2+ enters and leaves the cell across the SL membrane?

E: What fraction of the cell’s energy consumption is used for this purpose?

Explanation / Answer

A) amount of TnC present=70nmol/g wet weight

It is60% saturated at rest, thus active massis 60/100*70=42nmol/g

B) oxygen consumption for 1 gm weight of tissue=0.09ml

For 42 nmol/g, O2 required is 0.09x42=3.78ml

Energy required for 1 lt of O2=20.3kj

For 3.78 ml of O2= 20.3x1000/1000x3.78

=76.734j

C) Energy required is 57 kj

Fraction of energy used up= 76.734/57000

D)80% of the TnC used comes from SL

80/100×42=33.6

E) energy used for this purpose is same as (C) i.e.76.734/57000

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