fg-9041 and zinc-chloride

Glial cells in fiber tracts express various functional transmitter receptors, e.g., got glutamate. However, little is known about their biophysical and pharmacological profile. Using the in situ patch-clamp technique, kainate- and AMPA-induced conductance changes of glial precursor cells in the rat corpus callosum were investigated to study these aspects. Precursor cells were identified by their voltage-gated currents and were easily discernable from astrocytes and oligodendrocytes. Kainate induced two overlying effects in these cells: the activation of a cationic current and the block of potassium conductances. Cesium in the pipette solution blocked potassium conductances nearly completely and the ionic profile of the kainate-induced cationic current could be studied in detail. Full replacement of the sodium in the bath by calcium resulted only in a small kainate-induced (calcium) inward current flow, but the kainate-induced outward current carried by Cs+ was less affected reflecting a weak calcium permeability. The kainate response could be blocked by 6,7-dinitroquinoxaline-2,3-dione (DNQX) and millimolar zinc concentrations. Co-application of micromolar concentrations of zinc slightly enhanced the kainate-induced current, while Evans Blue was without any significant effect. Cyclothiazide increased the kainate response by a factor of x6 while concanavalin A did not enlarge it. The AMPA-induced current was amplified by a factor of x39 by cyclothiazide. The present data suggested the expression of weakly calcium-permeable AMPA receptors on glial precursor cells in the rat corpus callosum. Only a small fraction of the agonist-induced current could be seen without the appropriate blockers of receptor desensitization. An additional expression of kainate-preferring glutamate receptors could not be shown.

Topics: Animals; Benzothiadiazines; Calcium; Chlorides; Concanavalin A; Corpus Callosum; Diuretics; Evans Blue; Kainic Acid; Neuroglia; Patch-Clamp Techniques; Quinoxalines; Rats; Receptors, AMPA; Receptors, Kainic Acid; Sodium Chloride Symporter Inhibitors; Zinc Compounds