Controlling drug activity with light offers the possibility of enhancing pharmacological selectivity with spatial and temporal regulation, thus enabling highly localized therapeutic effects and precise dosing patterns. Here we report on the development and characterization of what is to our knowledge the first photoswitchable allosteric modulator of a G protein-coupled receptor. Alloswitch-1 is selective for the metabotropic glutamate receptor mGlu5 and enables the optical control of endogenous mGlu5 receptors.

The trabecular meshwork is a tissue located in the anterior chamber angle of the eye, and it is a crucial determinant of intraocular pressure values because of its resistance to the evacuation of aqueous humor from the eye. Here we bring together classical and recent discoveries on the function of the trabecular meshwork, keys to understanding eye pathophysiology.

Control of membrane traffic: Photoswitchable inhibitors of protein-protein interactions were applied to photoregulate clathrin-mediated endocytosis (CME) in living cells. Traffic light (TL) peptides acting as "stop" and "go" signals for membrane traffic can be used to dissect the role of CME in receptor internalization and in cell growth, division, and differentiation.

We describe a new approach for making real-time measurements of exocytosis and endocytosis in neurons and neuroendocrine cells. The method utilizes interference reflection microscopy (IRM) to image surface membrane in close contact with a glass coverslip (the "footprint"). At the synaptic terminal of retinal bipolar cells, the footprint expands during exocytosis and retracts during endocytosis, paralleling changes in total surface area measured by capacitance. In chromaffin cells, IRM detects the fusion of individual granules as the appearance of bright spots within the footprint with spatial and temporal resolution similar to total internal reflection fluorescence microscopy. Advantages of IRM over capacitance are that it can monitor changes in surface area while cells are electrically active and it can be applied to mammalian neurons with relatively small synaptic terminals. IRM reveals that vesicles at the synapse of bipolar cells rapidly collapse into the surface membrane while secretory granules in chromaffin cells do not.

We investigated the Ca 2؉ signal regulating fast exocytosis at the ribbon synapse of retinal bipolar cells by using total internal reflection fluorescence microscopy to image fluorescent Ca 2؉ indicators and interference reflection microscopy to monitor exocytosis. Depolarization generated Ca 2؉ ''microdomains'' that expanded over the time scale during which the rapidly releasable pool (RRP) of vesicles was released (<40 ms). Replacing mobile Ca 2؉ buffers in the terminal with 10 mM EGTA prevented expansion of microdomains and decreased the number of rapidly releasable vesicles by a factor of 2. Conversely, decreasing the concentration of EGTA in the terminal to 0.1 mM increased the apparent width of a Ca 2؉ microdomain from 580 nm to 930 nm and increased the size of the RRP size by a factor of 1.5. The [Ca 2؉ ] over the area that the microdomain expanded was estimated to be 2-7 M. These results indicate that vesicles within the RRP are located hundreds of nanometers from Ca 2؉ channels, and that fusion of these vesicles can be triggered by low micromolar levels of Ca 2؉ . Variable distances between docked vesicles and Ca 2؉ channels at the active zone, therefore, provide an explanation for the heterogeneous release probability of vesicles comprising the RRP.