Glycogen

Question 1

glycogen cannot leave muscle because myocytes lack which enzyme?

Answer 1

muscle does NOT express glucose-6-phosphatase —> all stored glycogen is used by the muscle tissue (cannot disperse into bloodstream as liver can)

Question 2

what are the hallmarks of hepatic vs muscle glycogen metabolism disorders, and why does this make sense?

Answer 2

hepatic glycogen metabolism disorders —> fasting hypoglycemia, hepatomegaly

muscle glycogen metabolism disorders —> muscle pain/cramps, exercise intolerance, myoglobinuria, variable cardiomyopathy

this makes sense because liver maintains fasting glucose levels (via glucose-6-phosphatase), while muscle keep glycogen stores to itself (selfish tissue)

Question 3

what is the purpose of PAS-D staining?

Answer 3

PAS-D = periodic acid-Schaffer-diastase (amylase)

differentiates glycogen - appears magenta on PAS stained slide, absent on PAS-D slide

Question 4

what is the forearm ischemic exercise test (FIET) use for?

Answer 4

helps diagnose metabolic disorder of muscle function - failure to elevate lactate in blood collected from ischemically exercised muscles confirms an abnormality of glucose metabolism

serum lactate measured at rest, then again after a minute of hand-grip exercise with an inflated BP cuff