Figure 4.
Feed-forward hyperpolarization of SMCs by KIR channel activation by K+ and Vm. A small amount of K+ released from neurons or astrocytes during neuronal activity may activate KIR channels on the SM and possibly also diffuse to KIR channels on ECs. Activation of KIR channels initiates membrane hyperpolarization, in the process promoting further KIR channel activation to amplify hyperpolarization and lead to Vm reaching EK. EC hyperpolarization, either due to K+ activation of KIR or resulting from conducted signaling from downstream capillaries, could also be transmitted to the SMs by gap junctions, further amplifying SMC hyperpolarization.