Key pointsr A planar nanocrystalline diamond array with nine ultra-microelectrodes (9-Ch NCD-UMEA) has been designed for high spatial resolution of amperometric recordings in single chromaffin cells.r The 9-Ch NCD-UMEA operates in voltammetric and amperometric mode to reveal low doses of adrenaline, dopamine and serotonin. The lowest detectable concentration of adrenaline is ß5 μM.r Using mouse and bovine chromaffin cells, single quantal exocytotic events are recorded from nine microareas of 12-27 μm 2 . We found an excellent correspondence with recordings from the cell apex using carbon fibre electrodes. r In the bovine, secretion is heterogeneous. There are areas of high and medium activity covering 54% of the cell surface and areas of low and no activity covering the remainder. The 'non-active zones' (silent) cover 24% of the cell surface and persist for minutes as the 'active zones' . r The 9-Ch NCD-UMEA brings new insights into the spatial mapping of secretory sites in chromaffin cells.Abstract Here we describe the ability of a high-density diamond microelectrode array targeted to resolve multi-site detection of fast exocytotic events from single cells. The array consists of nine boron-doped nanocrystalline diamond ultra-microelectrodes (9-Ch NCD-UMEA) radially distributed within a circular area of the dimensions of a single cell. The device can be operated in voltammetric or chronoamperometric configuration. Sensitivity to catecholamines, tested by dose-response calibrations, set the lowest detectable concentration of adrenaline to ß5 μM. Catecholamine release from bovine or mouse chromaffin cells could be triggered by electrical stimulation or external KCl-enriched solutions. Spikes detected from the cell apex using carbon fibre microelectrodes showed an excellent correspondence with events measured at the bottom of the cell by the 9-Ch NCD-UMEA, confirming the ability of the array to resolve single quantal secretory events. Subcellular localization of exocytosis was provided by assigning each quantal event to one of the nine channels based on its location. The resulting mapping highlights the heterogeneous distribution of secretory activity in cell microdomains of 12-27 μm 2 . In bovine chromaffin cells, secretion was highly heterogeneous with zones of high and medium activity in 54% of the cell surface and zones of low or no activity in the remainder. The 'non-active' ('silent') zones covered 24% of the total and persisted for 6-8 min, indicating stable location. The 9-Ch NCD-UMEA therefore appears suitable for investigating the microdomain organization of neurosecretion with high spatial resolution.

Turturici M, Mohammed M, Roatta S. Evidence that the contraction-induced rapid hyperemia in rabbit masseter muscle is based on a mechanosensitive mechanism, not shared by cutaneous vascular beds. J Appl Physiol 113: 524 -531, 2012. First published June 7, 2012 doi:10.1152/japplphysiol.00237.2012.-Several mechanisms have been hypothesized to contribute to the rapid hyperemia at the onset of exercise. The aim of the present study was to investigate the role played by the mechanosensitivity of the vascular network. In 12 anesthetized rabbits blood flow was recorded from the exclusively muscular masseteric artery in response to brief spontaneous contractions (BSC) of the masseter muscle, artery occlusion (AO), muscle compression (MC), and muscle stretch (MS). Activation of masseter muscle was monitored by electromyography (EMG). Responses to AO were also recorded from the mostly cutaneous facial and the central ear arteries. Five animals were also tested in the awake condition. The hyperemic response to BSC (peak amplitude of 394 Ϯ 82%; time to peak of 1.8 Ϯ 0.8 s) developed with a latency of 300 -400 ms from the beginning of the EMG burst and 200 -300 ms from the contractioninduced transient flow reduction. This response was neither different from the response to AO (peak amplitude ϭ 426 Ϯ 158%), MC, and MS (P ϭ 0.23), nor from the BSC response in the awake condition. Compared with the masseteric artery, the response to AO was markedly smaller both in the facial (83 Ϯ 18%,) and in the central ear artery (68 Ϯ 20%) (P Ͻ 0.01). In conclusion, the rapid contractioninduced hyperemia can be replicated by a variety of stimuli affecting transmural pressure in muscle blood vessels and is thus compatible with the Bayliss effect. This prominent mechanosensitivity appears to be a characteristic of muscle and not cutaneous vascular beds. muscle stretch; myogenic response; rapid dilatation; reactive hyperemia; muscle compression SKELETAL MUSCLE BLOOD FLOW has long been known to exhibit a rapid increase at the onset of exercise (1,9,12,22,27). The mechanisms behind this phenomenon are still a matter of debate despite the many new insights provided by different research groups in recent years. In particular it has been shown that the contraction-induced compression of venous compartments (muscle pump) cannot fully account for the blood flow increase and that the additional occurrence of a rapid active dilatation is required (18,33,45,46). Other studies have shown that this rapid dilatation is mediated neither by changes in sympathetic neural drive (7, 41), nor by ACh spillover from the motor endplate (6, 33), nor by endothelium-released NO (6), although this last assertion is debated (see DISCUSSION). As early as 1974, Mohrman and Sparks (31) hypothesized that the rapid dilatation could result from the myogenic response of muscle blood vessels to decreased transmural pressure, which in turn results from the increase in intramuscular (extravascular) pressure produced by the contraction. They showed, in fact, that the rapid hypere...

In conclusion, for its high sensitivity and reliability this technique is adequate to characterize mechano-vascular reactivity and may prove useful in the investigation of the underlying mechanisms, with implications in the control of vascular tone and blood pressure in health and disease.

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The complex interplay of neural, metabolic, myogenic and mechanical mechanisms that regulate blood flow in skeletal muscle (MBF) is still incompletely understood. For the first time, a method is presented for high time-resolution recording of MBF from a purely muscular artery in physiological conditions. Ultrasound perivascular flow probes were implanted (n = 15) mono- or bilaterally around the masseteric branch of the facial artery in nine rabbits and tested up to 16 days after implant. Reliable and stable recordings were achieved in 50% of implants. Blood flow was observed to increase from a resting level of 0.2-0.3 ml min(-1) up to 4.0-6.0 ml min(-1) during spontaneous masticatory activity. In addition, within single masticatory cycles marked back flow transients could be observed (peak flow = -10 ml min(-1)) during powerful masticatory strokes but not during mild mastication. The possibility of (1) surgically removing the sympathetic supply to the relevant vascular bed and of (2) bilaterally monitoring the perfusion of masseter muscles thus allowing to use one side as control side for different types of interventions makes this model a useful tool for disentangling the different mechanisms involved in the control of MBF.