Am I correct in my thinking about cyclic AMP?

Question

I've been working on this for awhile, but I'm not sure if I'm really getting it. If a patient injects, into the venous system, a polar molecule that, when placed in a test-tube with isolated protein kinase A, completely inhibits the activity of protein kinase A predict the respiratory and cardiovascular effects.(physiologic effects)

I predicted the respiratory effects to be: bronchoconstriction and the cardiovascular system effects to be:lowered heart rate, decreased contractility, and vasodiltion.

I'm worried that because the molecule is polar, target cells can't respond to the molecule?(since beta receptors require epinephrine?) which is correct?

What if the molecule were polar cyclic AMP? Can receptors respond to that since its not epinephrine? I'm thinking it may not produce any effects at all. Someone set me straight on this.

Answer 1

Your prediction of the physiological effects of the polar molecule that inhibits protein kinase A activity is partially correct. Protein kinase A is an enzyme that plays a crucial role in many cellular processes, including the regulation of cardiovascular and respiratory function. Inhibition of protein kinase A activity could lead to decreased heart rate, decreased contractility, and vasodilation, which could result in decreased blood pressure and decreased perfusion to the lungs.

However, it is unlikely that the polar molecule injected into the venous system would directly affect protein kinase A activity in vivo, as it may not be able to cross the cell membrane and reach the intracellular target. Additionally, the molecule may be rapidly cleared from the bloodstream by the liver or kidneys before it can exert any physiological effects.

Regarding your question about cyclic AMP, it is a signaling molecule that is produced in response to the binding of certain hormones or neurotransmitters to their receptors on the cell surface, including beta-adrenergic receptors that respond to epinephrine. Cyclic AMP can activate protein kinase A and other downstream signaling pathways, leading to physiological effects such as vasodilation and bronchodilation. However, if a polar form of cyclic AMP is injected into the bloodstream, it may not be able to cross the cell membrane and activate the downstream signaling pathways. Therefore, it is unlikely to produce any physiological effects in vivo.

Answer 2

Naina is correct. They specify that this molecule is polar so that it's clear that it stays soluble and will effect proteins in the blood the plasma and proteins in the cytosol of the cells. If it were non-polar you would expect to enter the membranes and have a more prominent effect on the cellular membranes and integral membrane proteins/receptors.

Answer 3

Hi Larissa

 

A simple  way of thinking about this is that molecule is an inhibitor for protein kinase A.  Every pathway  requiring Protein-kinase A mediated phosphorylation would be affected.

 

Find out the effects of  protein-kinase inhibition on respiratory and cardiovascular system and effect of various inhibitors. Based on that one can formulate a presumption about the molecule. It I better to interpret that molecular belongs toa particular class of inhibitors rather than concluding it as a specific compound.

 

Hope this helps.