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Addition of norepinephrine to a solution bathing an isolated cardiac papillary muscle leads to an increase in amount of work performed by the muscle at a given load with out changing the muscles initial length. The increase in work done by the muscle at its new steady state level is the result of an increase in which if the following

A)overlap of thin and thick filaments at the initial length
B)Sarcoplasmic calcium concentration while the load is lifted
C) Sarcoplasmic phosphocreatine concentration
4)Stiffness of series elastic elements

hi ....b...is more likely to be my answer...this is a case of isometric contraction of the papillary muscle in a solution (in my assumption that solution has high cacium concentration ...remember cardiac muscle relies on extracellular calcium concentration unlike skeletal muscle....)...

---and when norepinephrine is added it increases the intracellular calcium concentration ...to maintain the isometric contraction