Question

Malignant hyperthermia is a genetic abnormality in which exposure to certain agents, especially the widely used general anes. thetic halothane, produces a dramatic rise in body temperature, acidosis, hyperkalemia, and muscle rigidity. Death is rapid if the condition is untreated and may occur the first cime a susceptible person is anacstictiad. The defect causes an inappropriate release of \(\mathrm{Ca}^{2+}\) from the sarcoplasmic reticulum of muscle. Many heat-producing processes are stimulated in an uncontrolled fashion by the release of \(\mathrm{Ca}^{2+}\), including glycolysis and glycogenolysis. \(\mathrm{Ca}^{2+}\) increases glycogenolysis by A. activating phosphorylase kinase \(b\), even in the absence of \(c A M P\). B. binding to phosphorylase b. C. activating phosphoprotein phosphatase. D. inhibiting phosphoprotein phosphatase. E. protecting \(\mathrm{CAMP}\) from degradation.

Short answer

Answer: Activating phosphorylase kinase b, even in the absence of cAMP.

Step-by-step solution

Glycogenolysis is the process by which glycogen is broken down into glucose-1-phosphate (and ultimately glucose), allowing it to be used for energy production. It involves the action of several enzymes, including phosphorylase kinase, phosphorylase, and phosphoprotein phosphatase. #Step 2: Analyze the options# Now we will analyze each option to see which one best explains the role of \(\mathrm{Ca}^{2+}\) in increasing glycogenolysis. A. Activating phosphorylase kinase b, even in the absence of cAMP.

Phosphorylase kinase activates glycogen phosphorylase, which is responsible for breaking down glycogen. Phosphorylase kinase is itself activated by \(\mathrm{Ca}^{2+}\). So, this option could be true. B. Binding to phosphorylase b.

Phosphorylase b is an inactive form of glycogen phosphorylase. The activation of glycogen phosphorylase is performed by phosphorylase kinase, rather than by direct interaction with \(\mathrm{Ca}^{2+}\). Therefore, this option is not true. C. Activating phosphoprotein phosphatase.

Phosphoprotein phosphatase is an enzyme that dephosphorylates and inactivates glycogen phosphorylase, leading to decreased glycogenolysis. Thus, activating phosphoprotein phosphatase would not increase glycogenolysis, so this option is not true. D. Inhibiting phosphoprotein phosphatase.

If \(\mathrm{Ca}^{2+}\) inhibits phosphoprotein phosphatase, it would prevent the dephosphorylation and inactivation of glycogen phosphorylase. This would lead to increased glycogenolysis. This option is plausible. E. Protecting cAMP from degradation.

cAMP is a signaling molecule involved in the activation of phosphorylase kinase, among other cellular processes. However, the protection of cAMP from degradation is not directly related to the \(\mathrm{Ca}^{2+}\) ion, so this option is not true. #Step 3: Determine the correct option# After analyzing all the options, we found that option A (activating phosphorylase kinase b, even in the absence of cAMP) and option D (inhibiting phosphoprotein phosphatase) are both plausible explanations for how \(\mathrm{Ca}^{2+}\) increases glycogenolysis. However, option A is a more direct effect of \(\mathrm{Ca}^{2+}\) on the enzymes involved in glycogenolysis, whereas option D is an indirect effect. Therefore, the correct answer is: **A. Activating phosphorylase kinase b, even in the absence of cAMP.**