Homeostasis of neuronal activity is crucial to neuronal physiology. In dendrites, hyperpolarization-activated cyclic nucleotide-gated channel (HCN) 1 is considered to play critical roles in this process. While electrophysiological Studies have demonstrated the dynamic modulation Of 1(h) Current mediated by HCN1 proteins, little is known about the Underlying molecular and cellular mechanisms. In this study, we utilized cortical cultured neurons and biochemical methods to identify molecular and cellular mechanisms that mediate the physiological regulation of HCN1 channel functions in cortical neurons. Pharmacological manipulations of neuronal activity resulted in changes in the expression level of HCN1. In addition, the surface expression of HCN1 was dynamically regulated by neuronal activity. Both of these changes led to functional modulations of HCN I channels. Our study suggests that coordinated changes in protein expression and surface expression of HCN1 serve as the key regulatory mechanisms controlling the function of endogenous HCN1 protein in cortical neurons. (C) 2009 Elsevier Inc. All rights reserved.