Secretion: Dense-core vesicles can kiss-and-run too Cristina R Artalejo, Abdeladim Elhamdani, H.Clive Palfrey  Current Biology  Volume 8, Issue 2, Pages R62-R65 (January 1998) DOI: 10.1016/S0960-9822(98)70036-3

Figure 1 At the top is shown the oxidation reaction which converts catecholamines to quinones and which, in the presence of an electric field, generates electrons that can be measured by amperometry. Below is illustrated the set-up for patch amperometry [6]. The carbon fibre electrode is contained within a patch electrode, allowing the simultaneous recordings shown in the inset: catecholamine release (upper trace), capacitance increase (middle trace) and membrane conductance (lower trace). In the recordings shown, a dense-core vesicle attaches to the membrane via a flickering fusion pore (note noise in record) that allows passage of catecholamine recorded as a discrete foot signal not associated with the subsequent spike (top trace). Note that, at the asterisk, the fusion pore flickers open and closed, also reflected in the capacitance trace. Current Biology 1998 8, R62-R65DOI: (10.1016/S0960-9822(98)70036-3)

Figure 2 A comparison of the kiss-and-run and complete fusion models of dense-core vesicle exocytosis. In the complete fusion model (left), the dense-core vesicle membrane becomes continuous with the plasma membrane, and vesicle proteins mix with plasma membrane proteins. Secretion is by ‘degranulation’, in which the entire vesicular content is extruded. Catecholamine molecules are released from the matrix and all components enter the extracellular space. Retrieval is by coated pits, which become vesicles that carry dense-core vesicle membrane proteins to sites of new dense-core vesicle assembly. In the kiss-and-run model (right), dense-core vesicles connect to the membrane via a ‘fusion pore’. One possibility (shown) is that catecholamine release occurs through the fusion pore by ion exchange with incoming Na+ ions (counterions could also enter the vesicle across its own membrane [12]). Rapid endocytosis [11] ensues, pinching off the dense-core vesicle intact from the membrane. Refilling with new transmitter can then take place immediately, rapidly reforming a mature dense-core vesicle. Rings around retracting vesicles in both pathways represent dynamin, known to be involved in the pinch-off reaction. Current Biology 1998 8, R62-R65DOI: (10.1016/S0960-9822(98)70036-3)