The protein tyrosine kinase PYK2, which is highly expressed in the central nervous system, is rapidly phosphorylated on tyrosine residues in response to various stimuli that elevate the intracellular calcium concentration, as well as by protein kinase C activation. Activation of PYK2 leads to modulation of ion channel function and activation of the MAP kinase signalling pathway. PYK2 activation may provide a mechanism for a variety of short- and long-term calcium-dependent signalling events in the nervous system.

The family of mammalian genes related to the Drosophila Shaker gene, consisting of four subfamilies, is thought to encode subunits of tetrameric voltage-gated K+ channels. There is compelling evidence that subunits of the same subfamily, but not of different subfamilies, form heteromultimeric channels in vitro, and thus, each gene subfamily is postulated to encode components of an independent channel system. In order to identify cells with native channels containing subunits of one of these subfamilies (Shaw-related or ShIII), the cellular distribution of ShIII transcripts was examined by Northern blot analysis and in situ hybridization. Three of four ShIII genes (KV3.1, KV3.2, and KV3.3) are expressed mainly in the CNS. KV3.4 transcripts are also present in the CNS but are more abundant in skeletal muscle. In situ hybridization studies in the CNS reveal discrete and specific neuronal populations that prominently express ShIII mRNAs, both in projecting and in local circuit neurons. In the cerebral cortex, hippocampus, and caudate- putamen, subsets of neurons can be distinguished by the expression of specific ShIII mRNAs. Each ShIII gene exhibits a unique pattern of expression; however, many neuronal populations expressing KV3.1 transcripts also express KV3.3 mRNAs. Furthermore, KV3.4 transcripts are present, albeit at lower levels, in several of the neuronal populations that also express KV3.1 and/or KV3.3 mRNAs, revealing a high potential for heteromultimer formation between the products of three of the four genes. Expression of ShIII cRNAs in Xenopus oocytes was used to explore the functional consequences of heteromultimer formation between ShIII subunits. Small amounts of KV3.4 cRNA, which expresses small, fast-inactivating currents when injected alone, produced fast-inactivating currents that are severalfold larger when coinjected with an excess of KV3.1 or KV3.3 cRNA. This amplification is due to both an increase in single-channel conductance in the heteromultimeric channels and the observation that less than four, perhaps even a single KV3.4 subunit is sufficient to impart fast- inactivating properties to the channel. The oocyte experiments indicate that the apparently limited, low-level expression of KV3.4 in the CNS is potentially significant. The anatomical studies suggest that heteromultimer formation between ShIII proteins might be a common feature in the CNS. Moreover, the possibility that the subunit composition of heteromultimers varies in different neurons should be considered, since the ratios of overlapping signals change from one neuronal population to another. In order to proceed with functional analysis of native ShIII channels, it is important to known which subunit compositions might occur in vivo. The studies presented here provide important clues for the identification of native homo- and heteromultimeric ShIII channels in neurons.

GABAergic (GABA ‫؍‬ ␥-aminobutyric acid) neurons from different brain regions contain high levels of parvalbumin, both in their soma and in their neurites. Parvalbumin is a slow Ca 2؉ buffer that may affect the amplitude and time course of intracellular Ca 2؉ transients in terminals after an action potential, and hence may regulate short-term synaptic plasticity. To test this possibility, we have applied paired-pulse stimulations (with 30-to 300-ms intervals) at GABAergic synapses between interneurons and Purkinje cells, both in wild-type (PV؉͞؉) mice and in parvalbumin knockout (PV؊͞؊) mice. We observed pairedpulse depression in PV؉͞؉ mice, but paired-pulse facilitation in PV؊͞؊ mice. In paired recordings of connected interneuronPurkinje cells, dialysis of the presynaptic interneuron with the slow Ca 2؉ buffer EGTA (1 mM) rescues paired-pulse depression in PV؊͞؊ mice. These data show that parvalbumin potently modulates short-term synaptic plasticity.GABA ͉ cerebellum ͉ basket cells ͉ stellate cells ͉ Purkinje cells T he immediate consequences of past neuronal activity on synaptic strength are often examined by measuring the ratio (called paired-pulse ratio, or PPR) between the mean synaptic current in response to a test stimulation over that obtained with a conditioning stimulus. If the PPR is larger than 1, the synapse is considered as facilitating, whereas values smaller than 1 are characteristic of depressing synapses. However, facilitation and depression presumably coexist in all experimental conditions, and the PPR that is measured may be viewed as a balance between these two competing processes (1, 2).Current hypotheses link facilitation to the fact that some of the Ca 2ϩ ions entering the presynaptic terminal during the first stimulus are still present when the second stimulus is delivered (3, 4). Several modes of action have been envisaged for the residual calcium. It could act by binding to high affinity sites of the normal exocytosis machinery (5), by binding to special sites responsible for facilitation (2, 6), or by modulating the degree of saturation of high affinity Ca 2ϩ buffers (7, 8), but direct evidence in favor of any of these possibilities is still lacking.Depression is a complex phenomenon including both pre-and postsynaptic components. It may involve depletion of a readily releasable pool of vesicles, saturation or desensitization of postsynaptic receptors, or still other processes (7, 9).Calcium-binding proteins such as parvalbumin (PV), calretinin, and calbindin D 28k are important modulators of intracellular calcium dynamics in neurons (10) and could therefore influence both facilitation and depression. Effects of these calcium buffers are determined by their affinities for Ca 2ϩ ions and by the kinetics (on and off rates) of binding and releasing of Ca 2ϩ . PV is in this regard interesting because it has a slow dissociation rate (about 1 s Ϫ1 ) and a slow apparent association rate (about 10 7 M Ϫ1 ⅐s Ϫ1 ), due to the fact that Mg 2ϩ ions compete with Ca 2ϩ ions for binding. As a result...