In experiments, transient myocardial ischemia causes myocardial cells to increase in size. This effect is due in part to which of the following?

Question

In experiments, transient myocardial ischemia causes myocardial cells to increase in size.  This effect is due in part to which of the following?

Quizplus · Accepted Answer

When blood flow cannot meet myocardial demands, cardiac myocytes transition from aerobic to anaerobic metabolism. However, anaerobic metabolism cannot maintain proper intracellular ATP levels, and ADP, AMP and adenosine accumulate. Without ATP, the membrane Na⁺/K⁺-ATPases and the sarcoplasmic reticulum Ca²⁺-ATPases fail, leading to increased intracellular Na⁺ and Ca²⁺ and increased intramitochondrial Ca²⁺ concentrations. These increased concentrations attract free water, causing cellular and mitochondrial swelling. Failure of the sarcoplasmic reticulum to resequester Ca²⁺ leads to cessation of contraction within ischemic zones of myocardium. (Choice A) The cell membrane Na⁺/K⁺-ATPase pump normally brings K⁺ into the cell in exchange for Na+. Thus, in ischemic tissue, intracellular K⁺ is decreased. (Choice C) Cellular HCO₃^- is not elevated in cardiac ischemia. Anaerobic metabolism leads to lactic acid production and a decrease in pH. Tissue CO₂, the conjugate acid of HCO₃^-, is thus elevated in ischemic myocardium. (Choice D) Protein phosphorylation cascades play a role in a variety of processes including second messenger signaling and regulation of apoptosis. The cell's response to ischemia does involve initiating certain metabolic processes through protein phosphorylation, but this does not cause cell swelling. (Choice E) Ischemia causes a net solute gain within cardiac myocytes. Elevated concentrations of Na⁺ and Ca²⁺ draw free water into the cells, causing edema. Educational Objective: Ion pump failure due to ATP deficiency during cardiac ischemia causes intracellular accumulation of Na⁺ and Ca²⁺. The increased intracellular solute concentration draws free water into the cell, causing the cellular and mitochondrial swelling that is observed histologically.

In Experiments, Transient Myocardial Ischemia Causes Myocardial Cells to Increase