The code provided models an SK (small conductance) type calcium-activated potassium current, which is a critical component in neuronal excitability and signaling processes. Here's a detailed explanation of the biological mechanisms represented in the code:
SK Channels: These are a subtype of potassium channels that are activated by intracellular calcium ions (Ca²⁺). They are crucial for regulating membrane potential and contributing to afterhyperpolarization (AHP) following action potentials. The SK channels provide a feedback mechanism that modulates neuronal excitability based on intracellular calcium levels.
Calcium Dependency: The dynamics of SK channels heavily depend on the concentration of intracellular calcium (cai). A rise in intracellular calcium, typically due to influx through voltage-gated calcium channels or release from intracellular stores, increases the probability of SK channel opening.
cai (intracellular calcium concentration): This is the trigger for SK channel activation. The code uses the rates procedure to define the relationship between calcium concentration and channel gating (via zInf).
z (gating variable): Represents the fraction of open SK channels, ranging from 0 (closed) to 1 (fully open). The dynamic nature of z is characterized by its time evolution (z'), which models how quickly SK channels respond to changes in calcium concentration.
gSK_E2bar: This parameter represents the maximum possible conductance of the SK-type channels. It signifies the channel's capacity to allow potassium ions (K⁺) to flow through when fully open.
Modulation of Neuronal Firing: SK channels are involved in controlling the frequency and pattern of neuronal firing. By providing a hyperpolarizing K⁺ current in response to elevated calcium levels, these channels help terminate action potentials and prevent excessive firing that might lead to hyperexcitability.
Afterhyperpolarization (AHP): The potassium current generated through SK channels contributes to AHP, a period of reduced neuronal excitability following an action potential. This is crucial for pacing neuronal firing and shaping the overall firing pattern of neurons.
Synaptic Integration: In neurons, SK channels play an essential role in shaping synaptic responses and integrating synaptic input by modulating the membrane potential in response to activity-dependent calcium signals.
Neuronal Plasticity and Health: Proper functioning of SK channels influences various neural processes, including synaptic plasticity, learning, and memory. Additionally, dysregulation of SK channels can be implicated in neurological disorders, such as epilepsy and ataxia.
In summary, the code models the biophysical properties and functional role of SK-type calcium-activated potassium channels in neurons, particularly their involvement in the calcium-dependent regulation of membrane potential and neuronal excitability.