Single potassium channels in neuropile glial cells of the leech central nervous system

Pfl�gers Archiv European Journal of Physiology

1998

We have measured membrane current, membrane potential and intracellular Na+ and Ca2+ concentrations, [Na+]i and [Ca2+]i, of the giant glial cell in the nervous system of the leech Hirudo medicinalis using conventional microelectrodes and the fluorescent dyes sodium-binding benzofuran isophthalate (SBFI) and fura-2. When the Na+ was removed from the saline, the membrane conductance increased twofold from 1.29±0.1 µS to 2.57±0.18 µS (mean ± SEM; n=27). The rise in membrane conductance was accompanied by a current, which reversed around –74 mV, and the amplitude of K+-induced depolarizations or currents increased during Na+ removal, suggesting an increase in the K+ conductance of the glial membrane. We also monitored [Ca2+]i when removing external Na+ in the presence and absence of external Ca2+, and during injection of the Ca2+-chelator BAPTA into the cells. Our results indicate that Na+ modulates a K+ conductance of these glial cells, independent of intra- and extracellular Ca2+.

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Sodium-sensitive, calcium-independent potassium conductance in the leech giant glial cell

Nett

Pfl�gers Archiv European Journal of Physiology

1998

“…2). It is characterized mainly by a large K ϩ conductance (Kuffler and Potter, 1964), and different types of K ϩ channels have been identified (Mu ¨ller and Schlue, 1997;Nett and Deitmer, 1998a). The resting membrane potential of the giant glial cell varies between Ϫ50 mV and Ϫ75 mV.…”

Section: Resting Membrane Potentialmentioning

confidence: 99%

Leech giant glial cell: functional role in a simple nervous system

Rose

Munsch

et al. 1999

Glia

The giant glial cell in the central nervous system of the leech Hirudo medicinalis has been the subject of a series of studies trying to link its physiological properties with its role in neuron-glia interactions. Isolated ventral cord ganglia of this annelid offer several advantages for these studies. First, single giant glial cells can easily be identified and are quite accessible to electrophysiological and microfluorometric studies. Second, only two giant macroglial cells are located in the neuropil of each ganglion, rendering them well suited for studying neuron-glia interactions. Third, many neurons can be identified and are well known with respect to their physiology and their roles in controlling simple behaviors in the leech. This review briefly outlines the major recent findings gained by studying this preparation and its contributions to our knowledge of the functional role of glia in nervous systems. Emphasis is directed to glial responses during neuronal activity and to the analysis of intracellular Ca 2ϩ and H ϩ transients mediated by neurotransmitter receptors and ion-driven carriers. Among its numerous properties, the leech giant glial cell prominently expresses a large K ϩ conductance, voltage-dependent Ca 2ϩ channels, ionotropic non-NMDA glutamate receptors, and an electrogenic, reversible Na ϩ -HCO 3 Ϫ cotransporter.

“…Leech NG cells are equipped with Ca 2+ ‐dependent K + channels (Müller & Schlue 1997). Therefore, we studied a possible dependence of the myomodulin A‐induced hyperpolarization on extracellular Ca 2+ by removing Ca 2+ from the saline and adding 0.5 m m of the Ca 2+ chelator ethylene glycol‐bis‐(β‐aminoethyl ether)‐ N , N , N ′, N ′‐tetraacetic acid (EGTA).…”

Section: Resultsmentioning

confidence: 99%

Peptide‐mediated glial responses to Leydig neuron activity in the leech central nervous system

Schmidt

1999

Eur J of Neuroscience

Neuronal activity may lead to a variety of responses in neighbouring glial cells; in general, an ensemble of neurons needs to be active to evoke a K+- and/or neurotransmitter-induced glial membrane potential change. We have now detected a signal transfer from a single neuromodulatory Leydig neuron to the giant neuropil glial cells in the central nervous system of the leech Hirudo medicinalis. Activation of a Leydig neuron, two of which are located in each segmental ganglion, elicits a hyperpolarization in the giant neuropil glial cells. This hyperpolarization could be mimicked by bath application of the peptide myomodulin A (1 nM-1.0 microM). Myomodulin-like immunoreactivity has recently been found to be present in a set of leech neurons, including Leydig neurons (Keating & Sahley 1996, J. Neurobiol., 30, 374-384). The glial responses to Leydig neuron stimulation persisted in a high-divalent cation saline, when polysynaptic pathways are suppressed, indicating that the effects on the glial cell were direct. The glial responses to myomodulin A application persisted in high-Mg2+/low-Ca2+ saline, when chemical synaptic transmission is suppressed, indicating a direct effect of myomodulin A on the glial membrane. The glial hyperpolarization evoked by myomodulin A was dose dependent (EC50 = 50 nM) and accompanied by a membrane conductance increase of approximately 25%. Ion substitution experiments indicated that myomodulin A triggered a Ca2+-independent K+ conductance. Thus, our results suggest, for the first time, direct signal transmission from an identified modulatory neuron to an identified glial cell using a myomodulin-like peptide.