Chapter 4 - Ion Channels and Transporters Flashcards
In terms of ion channel currents, what are microscopic currents?
Microscopic currents are the currents that stem from ions moving through a single ion channel.
This question is meant to help you reflect on the scale of the topics covered in this chapter. A correct answer is not necessary.
The current passing through a single ion channel is measured in pA (pico-ampere, a billionth ampere). A current of 1 pA reflects the flow of hundres, thousands, millions or billions of ions per millisecond?
Thousands.
What is the relationship between microscopic Na+ currents and macroscopic Na+ currents?
They are similar, and all research indicates that the microscopic currents are responsible for the macroscopic currents.
The microscopic currents are responsible for the macroscopic currents. How many single ion channels would you need to observe to come to that conclusion?
More than one. This is because individual channels open and close in a random manner. Repeated depolarization of the membrane potential causes each Na+ channel to open and close many times. When the current responses to a large number of such stimuli are averaged together, the collective response has a time course that looks much like the macroscopic Na+ current.
“Fugu” is a pufferfish that can be ordered at specialized restaurants in Japan. Only chefs who have qualified three or more years of rigorous training are allowed to prepare the fish, and serving the tasty liver was banned in 1984. Why?
The fugu fish carries in its organs lethal doses of a toxin called tetrodotoxin. Tetrodotoxin produces a potent and specific obstruction of the Na+ channels responsible for action potential generation. This can completely paralyze a victim.
Genetic studies have identified genes in the human genome that code for more than X ion channels.
More than 100!
Na+ channels from many different cell types are dramatically different from each other. True or false?
False. They’re really quite similar. However, at least 10 genes for Na+ channels have been identified. This does indicate variation.
What is the most diverse class of voltage-gated ion channels?
The K+ channels.
The K+ channels are “by far the largest and most diverse class of voltage-gated ion channels”. How many are there, and what differences are found between types?
Nearly 100 K+ channels are known; these fall into several distinct groups that differ substantially in the action, gating, and inactivation properties.
Ion channels are often divided into groups based on their method of activation/inactivation. Mention 4 groups.
Voltage-gated ion channels.
Ligand-gated ion channels.
Strech-activated ion channels.
Heat-activated ion channels.
What are ligand-gated ion channels?
They are a class of ion channels that change the permeability of a membrane by reacting to signal molecules (ligands).
In a nerve cell, which ion is in electrochemical equilibrium? (Na+, K+. Cl-, Ca2+)
None of the ions of physiological importance are in electrochemical equilibrium.
What generates and maintains the concentrational gradients for the ions in the neuron?
Active transporters.
What are active transporters?
Active transporters are plasma membrane proteins that generate and maintain concentration gradients.
How do active transporters work?
Active transporters carry out their task by forming complexes with the ions they are translocating.
