Overdose on specific substances - Calcium Channel Blockers

Question 1

Calcium channel blockers act specifically to block calcium channels in what organ?

A. heart
B. adrenal glands
C. vasculature
D. brain stem

Answer 1

B. adrenal glands

Question 2

[Ca2+] is higher (intracellularly/extracellularly).

Answer 2

extracellularly

Question 3

By what 4 mechanisms to calcium channel blockers act to reduce blood pressure?

Answer 3

1. reduce vasoconstriction of arteries by preventing uncovering of tropomyosin. Calcium-troponin binding induces troponin conformation change, which uncovers tropomyosin. This prevents cross linkage of actin heads for contraction.
2. The same mechanism above occurs in cardiomyocytes (negative inotropic effect)
3. Slows the conduction of APs in phase 4 of the cardiac pacemaker cells
4. Blocking release of aldosterone from the adrenal cortex, which prevents activation of the RAAS

Question 4

Explain the mechanism of action by which calcium chloride overcomes CCB overdose.

Answer 4

CCB act through competitive inhibition. However, it is important to remember that calcium is NOT the substrate for calcium channels.

Instead, you are simply increasing the extracellular [Ca2+], hoping that the Ca2+ will flow into the cardiomyocytes and increase contractility/BP/HR.