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Old 07-31-2010
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Heart cardiac muscle contraction

Micro electrodes placed in cardiac muscle cells detect a rapid decrease in cytoplasmic calcium level immediately preceding relaxation. Which of the following mediates the observed response?

A- Voltage dependent calcium channels
B- Ryanodine receptors
C- Na/Ca exchanger pump
D- Troponin C
E- Calmodulin
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C, because
A- resp. for phase 2 of myocyte AP
B- found only in skeletal muscle
D- resp. for initation of actin/myosin cycling
E- found only in smooth muscle
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Old 07-31-2010
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yes the answer is C.

the easiest way to remember is the figure in kaplan pharmacology that describes the action of digoxin to block Na/K+ ATPase n then the increased in Na intracellular causes a block in Na/Ca exchange, thus increasing intracellular Ca2+ as well.
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Old 05-21-2012
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Quote:
Originally Posted by Androide89 View Post
C, because
A- resp. for phase 2 of myocyte AP
B- found only in skeletal muscle
D- resp. for initation of actin/myosin cycling
E- found only in smooth muscle
Ryanodine receptors (RyRs)are not restricted to striated muscle.
RyR1 is expressed predominantly in fast- and slow-twitch skeletal muscle
RyR2 was originally purified from cardiac muscle (it is the major isoform expressed there), but is also robustly expressed in neurons, and in visceral and arterial smooth muscle too.
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