Question

Primary Active Transporter Na+/K+ ATPase pump. Describe how this pump maintains Na+ and K+ ionic gradients across the cell membrane. SECONDARY ACTIVE TRANSPORTERS: How do these secondary transporters benefit from the ionic gradients created by primary active transporters? What is the difference between cotransport/countertransport?

(Please don't write the answer on a separate page all over the place. I'm new to A&P 1 and I'm still learning, so I need to be explained, rather than shown notes like what I take in class.)

Answer 1

Na+/K+ ATPase pump

It is called as a pump because it transport ions against its concentration gradient by using ATP.

• this pump is present on the cell membrane and it transports 3 sodium ions to the outside of the cell for each two potassium ions to the inside.
• so there is a net deficit of positive ions inside the cell. so this will result in a negative potential inside the cell when compared to outside. (Because of this pump, sodium ion outside is 142 mEq/L, sodium ion inside 14 mEq/L, potassium ion outside is 4 mEq/L , potassium ion inside is 140 mEq/L. )
• by looking at these concentration of ions , both inside and outside of the cell membrane , it's clear that these pumps work against concentration gradient (that is from lower concentration to higher concentration using ATP)
• it is actually needed for maintenance of resting membrane potential (only a minor role of nearly -4 mv) [remaining is by the diffusion of potassium and small quantities of sodium diffusion ]

SECONDARY ACTIVE TRANSPORTERS

For explaining this we need to consider the example of a co- transport

lets take the example of Na⁺ - glucose co transporter in the Proximal convoluted tubule of the kidney and Na⁺ - H⁺ counter transport.

1. Na+/K+ ATPase pump woks and because sodium is pumped outside there if deficit of sodium inside the cell.

2. this gradient can pull Na⁺ along with glucose using a carrier protein- its co-transport

3. this gradient can pull Na⁺ inside along with outward movement of H⁺ - its counter transport (two opposite directions)

co transport and counter transport requires carrier protein. i doesn't directly need ATP, and it works along the concentration gradient created by the primary active transport.

Note: there are other co-transporter and counter transporters in our body.

i hope its helps. please refer the image before going through pints 1,2,and 3.