Mast cells show dramatic morphological changes when undergoing exocytosis. We have investigated whether the first of those morphological changes, swelling of the secretory granule, precedes-and therefore possibly initiates-secretion or whether it occurs after fusion of the granule and plasma membranes. We used cell membrane capacitance to detect the moment when granule and plasma membrane become continuous. We measured large capacitance increases, often preceded by transients in capacitance. The rise-times of the capacitance increases were half-maximal at 2-59 msec. We observed cells with high-resolution video microscopy while these measurements were done. The capacitance increase always preceded the granular swelling that leads to exocytosis. To rule out the possibility that fusion was induced by a mechanical stress imparted by the internal pressure of a taut granule, we performed control experiments using cells in which vesicles were shrunken with hyperosmotic solutions. With these flaccid granules, again, the capacitance rise always preceded the swelling of the granules. We conclude that swelling cannot be the driving force for membrane fusion in this system.

The remarkable optical and electrical properties of nanostructured materials are considered now as a source for a variety of biomaterials, biosensing, and cell interface applications. In this study, we report the first example of hybrid bionanodevice where absorption of light by thin films of quantum confined semiconductor nanoparticles of HgTe produced by the layer-by-layer assembly stimulate adherent neural cells via a sequence of photochemical and charge-transfer reactions. We also demonstrate an example of nanoscale engineering of the material driven by biological functionalities.

A B ST R A C T Ba § ion blocks K § conductance at concentrations in the nanomolar range. This blockage is time and voltage dependent. From the time dependence it is possible to determine the forward and reverse rate constants for what appears to be an essentially first-order process of Ba ++ interaction. The voltage dependence of the rate constants and the dissociation constants place the site of interaction near the middle of the membrane field. Comparison of the efficacy of Ba § block at various internal K § concentrations suggests that Ba § is probably a simple competitive inhibitor of K + interaction with the K + conductance. The character of Ba ++ block in high external K + solutions suggests that Ba + § ion may be "knocked-off" the site by inward movement of external K § Examination of the effects of other divalent cations suggests that the channel may have a closed state with a divalent cation inside the channel. The relative blockage at different temperatures implies a strong interaction between Ba + § and the K § conductance.

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