CELLULAR pH Flashcards
On what scale is pH measured?
Logarithmic
What is the calculation for pH?
pH = -log [H+]
If the pH dropped from 7.4 to 7.1, what has happened to the [H+]?
It has increased by double.
What are protons important for?
- Important as a second messenger
2. Activation/inactivation of protein function for regulation
What are the methods that can be employed to measure intracellular pH?
- Microelectrodes - use of two microelectrodes to pierce the membrane of the cell. One of V1 containing a proton sensitive resin and V2 measuring everything. The voltage difference in the two electrodes is proportional to the proton concentration inside the cell.
- Fluorescent indicators - cells loaded with inactive form and trapped inside upon activation. The indicator is excited with a frequency of light, and when this occurs it emits another frequency of light. The amount of fluorescense is proportional to the pH. The cell is exposed to a proton ionophore making the membrane permeable to H+ so the pH inside the cell = pH outside of the cell. The pH of the proton ionophore bath = intracellular pH.
What are the controls of intracellular pH?
- Buffering System
- Acid Extrusion
- Acid Loading
What is a buffer?
Any system that moderates the effects of an acid or alkali load by consuming or releasing protons.
Action to minimise pH changes to protect the cell.
What is buffering power?
The amount of strong base/acid that must be added to a solution in order to raise/decrease the pH by a given amount.
If the pH increases, what is the action of the buffering system?
If the pH has increased there has been a decrease in proton concentration, therefore a proton donation must occur.
COOH —– COO- + H+
If the pH decreases what is the action of the buffering system?
If the pH has decreased then there has been an increase in proton concentration, therefore a proton must be accepted.
NH2 ——- NH3+
When does acid extrusion occur?
Acid extrusion occurs when there is a decrease in pH and therefore an increase in H+ concentration. After the buffer system has done as much as possible, a secondary system, the acid extrusion system must be activated in order to removed excess H+ from the cell.
Give an example of an exchanger that carries out acid extrusion and how it functions.
The Na/H exchanger exchanges intracellular H+ from extracellular Na+ in a one to one ratio.
This exchanger relies on the gradient set up by the Na/K ATPase.
The exchanger does a have set point - in alkaline environments it is inactive.
Has allosteric sites to increase the activity of the protein.
Give an example of a Na/H exchanger.
NHE1 - a housekeeping gene that regulates cell volume and pH.
What drugs inhibit the NHE1 exchanger?
Low concentrations of amiloride.
EIPA
When does acid loading occur?
When there is an increase in pH, there has been a decrease in proton concetration. After the buffer system has attempted to minimise this change, a secondary system is in place. Acid loading attempts to decrease the pH by moving protons back into the cell.
