Gap junctions are conductive channels that connect the interiors of coupled cells. We determined whether gap junctions propagate transcellular signals during metabolic stress and whether such signaling exacerbates cell injury. Although overexpression of the human proto-oncogene bcl2 in C6 glioma cells normally increased their resistance to injury, the relative resistance of bcl2+ cells to calcium overload, oxidative stress and metabolic inhibition was compromised when they formed gap junctions with more vulnerable cells. The likelihood of death was in direct proportion to the number and density of gap junctions with their less resistant neighbors. Thus, dying glia killed neighboring cells that would otherwise have escaped injury. This process of glial 'fratricide' may provide a basis for the secondary propagation of brain injury in cerebral ischemia.

Potassium channels play major roles in the regulation of many aspects of neuronal excitability. These channels are particularly well suited for such multiplicity of roles since there is a large diversity of channel types. This diversity contributes to the ability of specific neurons (and possibly different regions of the same neuron) to respond uniquely to a given input. Neuronal integration depends on the local response of spatially segregated inputs to the cell and the communication of these integration centers with the axon. Therefore, the functional implications of a given set of K+ channels varies depending on their precise location on the neuronal surface. Site-specific antibodies were utilized to characterize the distribution of KV3.1b, a subunit of voltage-gated K+ channels in CNS neurons. KV3.1b subunits are expressed in specific neuronal populations of the rat brain, such as cerebellar granule cells, projecting neurons of deep cerebellar nuclei, the substantia nigra pars-reticulata, the globus pallidus, and the ventral thalamus (reticular thalamic nucleus, ventral lateral geniculate and zona incerta). The KV3.1b protein is also present in various neuronal populations involved in the processing of auditory signals, including the inferior colliculus, the nuclei of the lateral lemniscus, the superior olive, and some parts of the cochlear nuclei; as well as in several other neuronal groups in the brainstem (e.g., in the oculomotor nucleus, the pontine nuclei, the reticulotegmental nucleus of the pons, trigeminal and vestibular nuclei, and the reticular formation) and subsets of neurons in the neocortex, the hippocampus and the caudate-putamen shown by double staining to correspond to neurons containing parvalbumin. KV3.1b subunits are localized predominantly in somatic and axonal membranes (particularly in axonal terminal fields) but are much less prominent in dendritic arborizations. This distribution is different than that of other subunits of voltage gated K+ channels and is consistent with a role in the modulation of action potentials. KV3.1b proteins have a cellular and subcellular distribution different than the related KV3.2 subunits which express in Xenopus oocytes currents similar to those expressed by KV3.1b.

Gap junctions are highly conductive channels that allow the direct transfer of intracellular messengers such as Ca 2ϩ and inositol triphosphate (IP 3 ) between interconnected cells. In brain, astrocytes are coupled extensively by gap junctions. We found here that gap junctions among astrocytes in acutely prepared brain slices as well as in culture remained open during ischemic conditions. Uncoupling first occurred after the terminal loss of plasma membrane integrity. Gap junctions therefore may link ischemic astrocytes in an evolving infarct with the surroundings. The free exchange of intracellular messengers between dying and potentially viable astrocytes might contribute to secondary expansion of ischemic lesions.

G-protein-gated inward rectifier potassium (GIRK) channels are coupled to numerous neurotransmitter receptors in the brain and can play important roles in modulating neuronal function, depending on their localization in a given neuron. Site-directed antibodies to the extreme C terminus of GIRK1 (or KGA1), a recently cloned component of GIRK channels, have been used to determine the relative expression levels and distribution of the protein in different regions of the rat brain by immunoblot and immunohistochemical techniques. We report that the GIRK1 protein is expressed prominently in the olfactory bulb, hippocampus, dentate gyrus, neocortex, thalamus, cerebellar cortex, and several brain stem nuclei. In addition to the expected localization in somas and dendrites, where GIRK channels may mediate postsynaptic inhibition, GIRK1 proteins were also found in axons and their terminal fields, suggesting that GIRK channels can also modulate presynaptic events. Furthermore, the distribution of the protein to either somatodendritic or axonal-terminal regions of neurons varied in different brain regions, which would imply distinct functions of these channels in different neuronal populations. Particularly prominent staining of the cortical barrels of layer IV of the neocortex, and the absence of this staining with unilateral kainate lesions of the thalamus, suggest that the GIRK1 protein is expressed in thalamocortical nerve terminals in which GIRK channels may mediate the actions of mu opiate receptors.