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Na+-selective, double-barrelled microelectrodes were used to measure intracellular Na+ activity (aiNa) and membrane potential (Em) in neuropile glial cells of isolated segmental ganglia in the leech Hirudo medicinalis. Bath application of glutamate (10(-3) M) resulted in membrane depolarizations of about 5 mV and a concomitant increase of aiNa by between 2 and 10 mM. Kainate (10(-4) M) elicited depolarizations of up to 40 mV amplitude followed by a prominent after hyperpolarization. During kainate, aiNa increased by 7 to 25 mM. In contrast to glutamate, an initial decrease of aiNa was detected during the action of kainate. N-methyl-D-aspartate (NMDA, 10(-5)-10(-3) M) had no effect of Em and aiNa. The results indicate that leech glial cells have a kainate-preferring non-NMDA glutamate receptor.

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In the cardia of larvae of Aedes aegypti Linnaeus 1758, Anopheles stephensi Liston 1901, Culex pipiens fatigans Wiedemann 1828, and Odagmia ornata Meigen 1818a single, tube-like peritrophic membrane is formed continuously which extends through the whole midgut and hindgut. Its fine structure differs in the genera which were investigated. The morphological differences are paralleled by biochemical dif ferences which could be visualized with lectins labelled with colloidal gold as an electron dense marker. Either peritrophic membranes or midgut epithelium or ultrathin sections of peritrophic membranes were incubated with lectin-gold conjugates. Specificity of binding could be determined by competition with the respective sugars. N-acetylglucosamine und N-acetylgalactosamine residues were found on both sides of the peritrophic membrane of these species. Fucose residues were localized only on the epithelium side of the peritrophic membrane of larvae of A. aegypti. The midgut epithelium of all species did not bind any of the lectins tested. Gel electrophoresis of the peritrophic membranes of blackfly larvae, Odagmia ornata, showed protein / glycoprotein bands with apparent molecular weights of 140, 130, 75, 63, 54, 22, 18, 16 and 12 kDa. Glycoproteins with specificity for soy bean agglutinin (SBA)-gold, which binds to N-acetyl galactosamine, with apparent molecular weights of 22, 18, 16 and 12 kDa could be demonstrated on nitrocellulose blots.

The pHi regulation from intracellular acidosis in the central nervous system appears to be mediated by mechanisms driven by the large inwardly directed Na+ gradient. The involvement of these mechanisms in pHi regulation of neurones and glial cells has been investigated in the leech central nervous system using ion-selective microelectrodes. For recovery from acidification, there appear to be three separate mechanisms: Na+/H+ exchange, Na(+)-dependent Cl-/HCO3- exchange, and Na+-HCO3- cotransport. All three mechanisms have a profound effect on the maintenance of pHi homeostasis in glial cells; whereas in leech neurones, as in other neuronal cells studied previously, the predominant mechanisms are Na+/H+ and Na(+)-dependent Cl-/HCO3- exchange. In addition to acid extrusion mechanisms we also found evidence for Na(+)-independent Cl-/HCO3- exchange. At alkaline pHi this exchanger may mediate some of the pHi recovery from intracellular alkalinization.