Question

increasing intracellular cAMP leads to smooth muscle relaxation by: Group of answer choices inhibiting IP3 channels, leading to decreased Ca2 in the sarcoplasm and reduced contraction. Increasing the relative activity of MLCP, leading to a decrease in tension. Activating K channels, increasing K leaking out of the cell which hyperpolarizes it and decreases the likelihood of Ca2 entry. Lower levels of MLCK activity, leading to decreased contraction.

Answer 1

1. Inhibiting IP3 channels, leading to decreased Ca2 in the sarcoplasm and reduced contraction.

2. Increasing the relative activity of MLCP, leading to a decrease in tension.

3. Activating K channels, increasing K leaking out of the cell which hyperpolarizes it and decreases the likelihood of Ca2 entry.

Step-by-step explanation

In smooth muscle, cyclic AMP (cAMP) mediates relaxation because cAMP inhibits a specific kinase required for myosin light chain protein (MLCP) phosphorylation, thereby triggering contraction in the smooth muscles. It has been shown that cAMP inhibits 1,4,5-trisphosphate (IP3)-dependent calcium ions (Ca 2+) release by activation of the cGMP-dependent protein kinase (PKG). PKG proteins act to modulate Ca2+ oscillations by stimulating sarcoplasmic Ca2+-ATPase membrane proteins, increasing Ca2+ in the sarcoplasmic reticulum stores and Ca2+ efflux from the cells, and activate voltage-gated potassium (K) channels, thereby leading to membrane hyperpolarization and reducing Ca2+ entry through Ca2+ channels.