Question

This question is about the potassium ion: 1) what does potassium do at the passive potassium channels of neurons, 2) what is the role for potassium in the voltage-gated potassium channels, and 3) what is the role of potassium in chemically-gated channels that open a channel for potassium? Also, for 1), 2), and 3), where are each of these located on the neuron?

Answer 1

1) There are several types of potassium channels, having its own pharmacological properties. A single neuron contains more than one type of potassium channel.

Depolarization of the membrane is caused by outward flow of the potassium. This occurs through the delayed rectifier channel (IDR), which, activated by the influx of Na+. By repolarizing the membrane, the IDR channel restricts the duration of the nerve impulse and participates in the regulation of the repetitive firing of the neuron.

IA channels are opened by depolarization following hyperpolarization because of the outward current. By increasing the interval between action potentials, neurons are able to fire repetitively at low frequencies.

IK(Ca) channel, is activated by high concentrations of intracellular Ca2+  results in hyperpolarization of the membrane so that they appear to slow the repetitive firing of nerve impulses.

The IM channel is opened by depolarization but is deactivated only by the neurotransmitter acetylcholine. This property may serve to regulate the sensitivity of neurons to synaptic input.

The rectifier channel (IIR)  closes with depolarization and opens with hyperpolarization, allowing an unusual inward diffusion of K+. The IIR channel prolongs depolarization of the neuron and helps produce long-lasting nerve impulses.