clar697
Forum Guru
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Addition of norepinephrine to a solution bathing in isolated cardiac papillary muscle leads to an increase in the amount of work performed by the muscle at a given load, without changing the muscle’s initial length. The increase in work done by the muscle at its new steady-state level is the result of an increase in which of the following?
A) Overlap of thick and thin filaments at the initial length
B) Sarcoplasmic Ca++ concentration while load is lifted
C) Sarcoplasmic phosphocreatinine concentration
D) Stiffness of the series elastic elements
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| hitesh
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B) Sarcoplasmic Ca++ concentration while load is lifted
NE will stimulate B1 receptors, which act by Gs>> c-AMP>> Ca2+ mechanism.
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| littledoc
Forum Newbie
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muscle,s length is not changed so preload is not changed, therefore increase in performance can be explained on the basis of incrased contractility. & contractility is due to Ca++
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| dkmj13
Forum Junior
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B) Sarcoplasmic Ca++ concentration while load is lifted
But the explanation is not directly related to Gs mech (PLC directly increases Ca++). It happens indirectly .
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| alirizvi
Forum Senior
Topics: 11
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Yea i dnt think its camp induce Ca++..
Its more with the phase 4 of S.A node. Gs will increase conductance to Na+ K+ K+ ..
Inc Na inc HR. Inc Ca+ in upstroke velocity. Inc K+ eflux dec AP duration.
When u have more Na inside cell due to inc conductance. You will stimulate the Na+Ca counter transport and increase Ca+ more and that can be Ca++ induced Ca++ activation at the SR pump.
Also with choice A. remember heart is never at Lo ( optimum length ? ) thats why u can inc PRELOAD, inc stretch and inc. cardiac output upto certain amount. But then if u go passed Lo then u will start dec cardiac output like congest heart failure etc.
And with choice B i dnt know because it says which will INCREASE and saroplasmic ca++ should decrease since it is being pumped out of SR.
so maybe C ? because protein kinase A does phosphorylate enzymes etc.. But phosphocreatine i have read about in skeletal muscle never in cardiac. However it does provide ATP anaerobicazlly. and SR has ATPase pump.
Edited by alirizvi on 10/01/08 - 09:06 AM
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