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cardiac inotropy - sao
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07-16-2006, 06:07 PM
Cardiac inotropy is enhanced by
a. Agonists coupled to Gi-protein. b. Decreased calcium binding to troponin-C. c. Decreased release of calcium by terminal cisternae. d. Protein kinase A phosphorylation of L-type calcium channels.
07-16-2006, 07:48 PM
The correct answer is œd because phosphorylation of the L-type calcium channels by protein kinase A increases the permeability of the channel to calcium, thereby permitting more calcium to enter the cell during depolarization, which triggers the release of calcium by the sarcoplasmic reticulum.
Choice œa is incorrect because Gi-protein activation decreases cAMP formation, thereby decreasing inotropy. Choice œb is incorrect because calcium binding to TN-C enhances inotropy. Choice œc is incorrect because it is the calcium that is released by the terminal cisternae of the sarcoplasmic reticulum that binds to TN-C leading to contraction |
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