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Jan 8, 2013
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Fellow SDNers,

I wanted to ask a question on the action potential(AP), Ca+2 transient and cardiac muscle twitch is affected when we either experimentally introduce more extracellular Ca+2 or administer isoproterenol.

From what I understand when you would increase the extracellular Ca+2 more would enter through the L-type channel resulting in a larger plateau phase of the AP, therefore more depolarization and hence more Ca+2 released from the sarcoplasmic reticulum(SR) by the action of the Ca+2 induced Ca+2 release (Ryanodine receptors on SR), if more Ca+2 released from SR then larger Ca+2 transient, but how would the rate of removal be affected based on SERCA/phospholamban?

Whereas isoproterenol, would decrease the duration of the AP because the cell would depolarize and repolarize faster, therefore the Ca+2 transient will increase rapidly but will also decreased rapidly because isoproterenol has effects on the phospholamban, as well?

All in all, could someone please give me some direction and explain to me how each of the three components would be affected and how the muscle twitch in the cardiac muscle will differ in the two scenarios?