Calcium clamp in single nerve cells

Control of local intracellular calcium concentration with dynamic-clamp controlled 2-photon uncaging

The variations of the intracellular concentration of calcium ion ([Ca(2+)](i)) are at the heart of intracellular signaling, and their imaging is therefore of enormous interest. However, passive [Ca(2+)](i) imaging provides no control over these variations, meaning that a full exploration of the functional consequences of [Ca(2+)](i) changes is difficult to attain. The tools designed so far to modify [Ca(2+)](i), even qualitatively, suffer drawbacks that undermine their widespread use. Here, we describe an electro-optical technique to quantitatively set [Ca(2+)](i), in real time and with sub-cellular resolution, using two-photon Ca(2+) uncaging and dynamic-clamp. We experimentally demonstrate, on neurons from acute olfactory bulb slices of Long Evans rats, various capabilities of this technique previously difficult to achieve, such as the independent control of the membrane potential and [Ca(2+)](i) variations, the functional knocking-in of user-defined virtual voltage-dependent Ca(2+) channels, and the standardization of [Ca(2+)](i) patterns across different cells. Our goal is to lay the groundwork for this technique and establish it as a new and versatile tool for the study of cell signaling.

Synaptic plasticity and Ca2+ signalling in astrocytes

There is a growing body of evidence suggesting a functional relationship between Ca2+ signals generated in astroglia and the functioning of nearby excitatory synapses. Interference with endogenous Ca2+ homeostasis inside individual astrocytes has been shown to affect synaptic transmission and its use-dependent changes. However, establishing the causal link between source-specific, physiologically relevant intracellular Ca2+ signals, the astrocytic release machinery and the consequent effects on synaptic transmission has proved difficult. Improved methods of Ca2+ monitoring in situ will be essential for resolving the ambiguity in understanding the underlying Ca2+ signalling cascades.

Glutamate-induced increases in intracellular free Mg2+ in cultured cortical neurons

Intracellular free Mg2+ concentrations ([Mg2+]i) in single rat brain neurons were measured with the Mg(2+)-sensitive fluorescent dye magfura-2. Addition of glutamate with glycine raised [Mg2+]i from 1 to more than 11 mM compared with the resting concentration of 0.5 mM, an effect mediated by N-methyl-D-aspartate receptors. Most of the increase in [Mg2+]i was independent of extracellular Mg2+, but was dependent on extracellular Ca2+. The second component of the increase induced by glutamate was independent of extracellular Ca2+, but required extracellular Mg2+ and was amplified by extracellular Na+ removal. These results indicate that regulation of [Mg2+]i by neurotransmitters such as glutamate may be important in controlling neuronal excitability.