The provided code models the BK (Big Potassium) channel, which is a type of calcium-activated potassium channel found in various cells, including neurons. BK channels are key regulators of cellular excitability and have been implicated in processes such as neurotransmitter release, muscle contraction, and the tuning of electrical activity in neurons.
Ion Specificity and Conductance: The model describes a potassium channel (BK channel), specifically indicated by the equilibrium potential EK = -0.09, which corresponds to the typical reversal potential for potassium ions (K⁺) in biological cells. These channels allow for the flow of potassium ions out of the neuron, which contributes to the hyperpolarization of the membrane potential.
Calcium Activation: BK channels are activated by intracellular calcium concentrations, as shown by y, which represents calcium levels in the code. Calcium binding to these channels increases their probability of being open, thus coupling membrane potential changes with the intracellular calcium signaling pathways.
Voltage Dependence: The code uses variables x, xmin, and xmax to represent membrane potential, affirming that the BK channel opening is also voltage-dependent. The exponent terms involving ZFbyRT reflect how channel kinetics change with the membrane potential, influencing a and b rates which likely represent state transitions for the channel.
Kinetics and Temperature Effects: The code calculates transition rates (a and b) that depend on voltage and calcium concentration, attempting to mirror experimental data from Berkefeld et al., 2006. Temperature effects are included through the variable Temp, setting conditions similar to those used in the referenced studies.
Empirical Calibration: Reference to Berkefeld et al., 2006 indicates that this model's parameters are empirically tuned to match observed data. The model primarily attempts to replicate BK channel behaviors under varying calcium concentrations, reproducing shifts in channel behavior such as activation thresholds and kinetics.
The model's key focus is to replicate the dual dependency of the BK channel on both membrane voltage and intracellular calcium concentration, reflecting its role in modulating the electrical properties of cells based on intracellular signaling and external voltages.