Flashcards in Membrane Transporters II Deck (9)
Some transporters act like ion channels, shuttling a single solute species in either direction. This is called _______. The best known example of this is the glucose transporter.
The glucose transporter will
transport glucose in either direction, and burns no energy in the process. Thus, it is not a pump.
How, then, do cells concentrate glucose?
The answer is that as soon as a glucose molecule gets into the cell, it is phosphorylated to Glucose-6-Phosphate. G-6-P doesn't fit on the transporter, and so is "trapped" inside. The empty ‘carrier’ can then ‘return’ to the outside of the membrane
in the absence of glucose,
the transporter is not even present in the plasma membrane; it is sequestered inside the cell
_______ triggers a biochemical cascade that causes the vesicle membranes to fuse with the surface membrane, exposing the _______ transporter to the ECF. The transporter then gets busy and ‘carries’ glucose inside. When insulin subsides, the transporter molecules are reinternalized.
Way cells are encouraged to take up K from the ECF: C
o Ca+2 ions bind to the outside surface of cell membranes. Through an electrostatic action, they trick the Na+ channels into thinking the membrane has been hyperpolarized. This increases threshold potential through a mechanism that is still unclear, thus restoring normal gradient between threshold for an action potential, quieting down the aberrant, spontaneous depolarization of individual cardiac cells.
o Screen the naked fixed negative charges in cell membranes
o Hyperpolarizes the local Vm
o Makes it more difficult for the cell to fire an action potential
o VERY LOCALIZED EFFECT!
Way cells are encouraged to take up K from the ECF: B
o The presence of excess bicarbonate ions will stimulate an exchange of cellular H+ for Na+, thus leading to stimulation of the sodium-potassium ATPase which will stimulate uptake of K+ into the cell
Way cells are encouraged to take up K from the ECF: I/G
Give Insulin and Glucose
o Similarly stimulates the Na+/K+ pump, drawing K+ into the cell from the blood