Sun10October0740PM 18

Which of the following best describes the pathway of endothelial nitric oxide (eNO)?

(Please select 1 option)

Inhibition of guanylyl cyclase, decreases cGMP concentration leading to vasoconstriction Incorrect answer selected

Stimulation of guanylyl cyclase, decreases cGMP concentration leading to vasodilation

Inhibition of guanylyl cyclase, increases cGMP concentration leading to vasodilation

Stimulation of guanylyl cyclase, increases cGMP concentration leading to vasoconstriction

Stimulation of guanylyl cyclase, increases cGMP concentration leading to vasodilation This is the correct answer

Explanation

Nitric oxide (NO) or endothelial-derived relaxant factor (EDRF) is a powerful vasodilator. It is a calcium-dependant cell-signalling molecule that is generated from nitric oxide synthetases from the precursor L-arginine. There are three main isoforms induceable (iNO), neuronal (nNO) and endothelial (eNO).

eNO stimulates intracellular guanylyl cyclase which generates cyclic GMP (cGMP) from an action on guanylyl tri-phosphate (GTP). The cGMP activates protein kinase G (PKG). PKG phosphorylates cell membrane proteins that regulate intracellular calcium concentrations and level of calcium sensitisation.

Vasodilatation of the smooth muscle results from:

Inhibition on calcium entry into the cell (reducing Ca2+ concentrations)

Hyperpolarisation of cells by activation of H+ channels, and

Activation of light chain phosphatase.

Answer Statistics

1

2%

2

11%

3

19%

4

3%

5

67%

Times answered: 242