Card 25 / 30: You have spent years to identify the gene for a rare, dominantly inherited paralytic disease. The disease is characterized by a temporary inability to generate action potentials in the muscle after heavy exercise. The gene you finally identify encodes an inwardly rectifying potassium channel, and the disease is correlated with a single amino acid change in its selectivity filter. Experiments on mutant channels expressed in cultured cells indicate that the channel becomes less selective for K+ when lactic acid builds up and the residue is protonated. What is the single most likely etiology for the disease?
A) Na+ influx depolarizes the muscle to a region where voltage-gated Na+ channels are largely inactivated.
B) Because the channel is less K+ -selective, K+ leaks into the muscle, shifting the K+ Nernst potential more negative and hyperpolarizing the cell
C) Ca2+ influx stimulates continuous neurotransmitter release, and desensitization of nACh receptors
D) K+ accumulation in the T-tubules depolarizes the muscle cells

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