Distinct modes of regulated receptor insertion to the somatodendritic plasma membrane.

Many neural signaling receptors are regulated by endocytosis, but little is known about receptor insertion into the plasma membrane. Time-lapse imaging of the beta2 adrenergic receptor expressed in cultured rat hippocampal neurons, using pH-sensitive green fluorescent protein tagging and total internal reflection fluorescence microscopy, resolved distinct vesicular fusion events mediating receptor insertion into the somatodendritic plasma membrane. A 'transient' insertion mode resulted in rapid lateral dispersion of receptors immediately after insertion. A 'persistent' insertion mode resulted in the retention of inserted receptors in surface-accessible domains, which were relatively immobile for a prolonged 'wait' period before dispersing laterally. Distinct insertion modes were oppositely regulated by receptor activation and by mechanisms differing in their dependence on the signaling effector cyclic AMP-dependent protein kinase. These results reveal a new mechanism for homeostatic regulation of postsynaptic signaling and a 'kiss-and-wait' mode of regulated membrane protein insertion in neurons.