Passive diffusion/calcium/thiazide diuretics

[Lothric]

Hey,

Thiazide diuretics can be given to treat kidney stones composed of calcium ions. The mechanism is blocking the sodium-chloride cotransporter in DCT which stimulates the sodium-calcium exchanger so that the [ca2+] intracellularly decreases. This will establish a concentration gradient for calcium ions, causing them to passively diffuse to the DCT cells from the urine.

This awoke the following question:

1. When ions diffuse the concentration gradient plays a central role. Does the concentration gradient only apply for one particular ion or is the gradient established from the sum of all solutes in two compartments separated by a permeable membrane?

E.g., because the intracellular calcium ion concentration is lower, the concentration gradient for calcium ions increases between urine and cell. However, there are overall still more solutes intracellularly (except for calcium ions when thiazide diuretics is given) than in urine.

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[sahell]

Depends on permeability. DCT has a Ca channel (stimulated by PTH), making it permeable. The principle applies as long as the solute is permeable.

When you say the sum of all solutes all that comes to mind is osmolalilty and that should only affect water transport if it's an effective osmole.

 

[Lothric]

Depends on permeability. DCT has a Ca channel (stimulated by PTH), making it permeable. The principle applies as long as the solute is permeable.

When you say the sum of all solutes all that comes to mind is osmolalilty and that should only affect water transport if it's an effective osmole.

Let's assume the membrane is permeable. So the concentration gradient only applies for one particular ion? Let's take sodium ions as an example and let's assume there are overall more solutes intracellularly than in blood plasma. Sodium ions would diffuse into the cell, right, because there are fewer of them inside the cell despite there overall being more solutes in the cell. Am I correct on this?

 

[sahell]

That's right. Na, K , Ca may all have different concentration gradients. If the membrane is permeable to the solute it will flow along its concentration gradient so as to reach equilibrium. The rate of diffusion will be proportional to the concentration gradient in simple diffusion.

 

[Lothric]

That's right. Na, K , Ca may all have different concentration gradients. If the membrane is permeable to the solute it will flow along its concentration gradient so as to reach equilibrium. The rate of diffusion will be proportional to the concentration gradient in simple diffusion.

Thank you for your help man.

 

[sahell]

No worries. I'd appreciate a like. Apparently I need a couple likes before I can post links (I guess so that people don't spam)