HETEROGENEITY OF ASTROCYTE RESTING MEMBRANE-POTENTIALS AND INTERCELLULAR COUPLING REVEALED BY WHOLE-CELL AND GRAMICIDIN-PERFORATED PATCH RECORDINGS FROM CULTURED NEOCORTICAL AND HIPPOCAMPAL SLICE ASTROCYTES

Astrocytes are thought to regulate the extracellular potassium concent ration by mechanisms involving both voltage-dependent and transport-me diated ion fluxes combined with intercellular communication via gap ju nctions, Mechanisms regulating resting membrane potential (RMP) play a fundamental role in determining glial contribution to buffering of ex tracellular potassium and uptake of potentially toxic neurotransmitter s. We have investigated the passive electrophysiological properties of cultured neocortical astrocytes and astrocytes recorded in hippocampa l slices from 18-25 d postnatal rats. These experiments revealed a wid e range of astrocyte RMPs that were independent of developmental facto rs, length of culturing, cellular morphology, the electrophysiological techniques used (whole-cell vs perforated recording), cell-specific e xpression of Na-/2HCO(3)(-) co-transporters, or voltage-dependent Nachannels. Exposure of cultured astrocytes to differentiation-inducing factor; (such as cAMP) or inhibition of proliferation (by serum depriv ation) did not significantly influence RMP. Expression of ATP-sensitiv e potassium channels was absent in these glia; thus, K-(ATP)-related m echanisms did not contribute to cell resting potential. In both cultur ed and slice astrocytes, spontaneous electrophysiological changes were commonly observed, These reversible events, which resulted in differe ntial sensitivity to potassium channel blockers (cesium and barium) an d sudden current-voltage profile changes, were attributable to dynamic changes in cell-to-cell coupling, as confirmed by recordings from iso lated pairs of cells. We conclude that the heterogeneity of astrocytic RMP and intercellular coupling both in culture and in situ are intrin sic properties of glia that may contribute to transcellular transport of potassium, We propose a model in which spatial buffering may be fac ilitated by heterogeneous mechanisms controlling glial RMP in combinat ion with dynamic changes in intercellular coupling.