Final answer:
Epinephrine and norepinephrine increase cardiac calcium levels by phosphorylating calcium channels and enhancing calcium-ATPase activity, both facilitating greater calcium ion influx and availability for heart muscle contractions.
Step-by-step explanation:
Mechanisms by which epinephrine and norepinephrine enhance the amount of calcium in cardiac muscle cells during a fight-or-flight response include the phosphorylation of calcium channels and the enhancement of calcium-ATPase activity. When epinephrine and norepinephrine bind to beta-1 receptors, a cascade of events is triggered that culminates with the phosphorylation of calcium channels, resulting in an increased influx of calcium ions into the cardiac cells. Additionally, the activity of calcium-ATPase, an enzyme that pumps calcium out of the cytoplasm into the sarcoplasmic reticulum, is heightened, which indirectly increases the amount of calcium available during each cardiac contraction because more is rapidly sequestered and then released with each heartbeat.