The voltage-sensitive sodium channel confers electrical excitability on neurons, a fundamental property required for higher processes including cognition. The ion-conducting ␣-subunit of the channel is regulated by two known auxiliary subunits, ␤1 and ␤2. We have identified rat and human forms of an additional subunit, ␤3. It is most closely related to ␤1 and is the product of a separate gene localized to human chromosome 11q23.3. When expressed in Xenopus oocytes, ␤3 inactivates sodium channel opening more slowly than ␤1 does. Structural modeling has identified an amino acid residue in the putative ␣-subunit binding site of ␤3 that may play a role in this difference. The expression of ␤3 within the central nervous system differs significantly from ␤1. Our results strongly suggest that ␤3 performs a distinct neurophysiological function.T he voltage-sensitive sodium channel plays a fundamental role in excitable cells, transiently increasing the sodium permeability of the plasma membrane in response to changes in membrane potential and thus propagating the action potential (1, 2). Not surprisingly, mutations in sodium channel genes are implicated in several pathologies, including epilepsy and cardiac arrhythmias (3-5), and therapeutic drugs, including antiepileptics, local anesthetics, and anticonvulsants (6), act on the channel.In the central nervous system, the channel is conventionally described as a heterotrimer composed of a 260-kDa ␣-subunit, a noncovalently associated 36-kDa ␤1-subunit, and a disulfidelinked 33-kDa ␤2-subunit (2). The ␣-subunit forms the ion pore and is responsible for the voltage-sensitive characteristics of the complex. There are multiple isoforms of the ␣-subunit expressed in different regions of the brain and peripheral nervous system that differ in their kinetic properties (1). The ␤-subunits are auxiliary components acting in a regulatory capacity (7). ␤1 increases the fraction of ␣-subunits operating in a fast gating mode, thus accelerating the activation and inactivation kinetics of the channel and modulating the frequency with which neurons fire (8). The ␤2-subunit is required for the efficient assembly of the channel but has minor effects on gating kinetics. These two ␤-subunits are distantly related by sequence (9).We now report the cloning and analysis of the rat and human forms of a previously uncharacterized sequence that we call ␤3. It is homologous to ␤1, but differs from ␤1 both in its distribution within the brain and in some of its kinetic properties. The discovery of this subunit increases the complexity of the sodium channel and raises further questions about the role of these auxiliary subunits. Materials and MethodsCloning Methodology. We isolated a variant of the rat pheochromocytoma cell line PC12 (termed A35C), which lacks typical neuronal properties (10). To discover previously unidentified neuroendocrine-specific genes, subtractive cloning was used to identify transcripts expressed at a level in the variant cells lower than that in normal PC12 cells. Total RNA wa...

PD134308 and PD135158 are potent and selective antagonists at the cholecystokinin type B (CCK-B) receptors with ICSO values of 1.6 nM and 3.5 nM, respectively, in the radioligand binding assay andKe values of7.82 and 12.9 nM, respectively, in their blocking action on CCK responses in the rat lateral hypothalamic slice. PD134308 and PD135158 produced potent anxiolytic effects in the mouse black/white box test after either subcutaneous or oral administration. There was no evidence of the development of tolerance to the anxiolytic action of either PD134308 or PD135158 in mice treated twice daily for 7 days, nor was there any sign of withdrawal anxiogenesis after abrupt termination of this treatment. Both CCK-B antagonists were able to suppress the withdrawal anxiogenesis and produce an anxiolytic effect in mice previously made tolerant to diazepam. PD134308 and PD135158 produced potent anxiolytic effects in the rat elevated plus maze test and the rat social interaction test. The effects were comparable in magnitude to those seen with diazepam. However, unlike diazepam, PD134308 and PD135158 did not produce sedation. The CCK-B antagonists also showed powerful anxiolytic activity in the "marmoset human threat test." These results provide evidence of a selective role for CCK-B receptors in the control of anxiety.PD134308 and PD135158 are members of a class of anxiolytic agents that have a greatly improved prorfle compared with benzodiazepines or serotonin-related anxiolytics.

1 This study examined the action of gabapentin (gabapentin,1-(aminomethyl) 2+ in¯ux were signi®cantly reduced by *25-30% in the presence of gabapentin (25 mM). 4 Gabapentin potently inhibited the peak whole-cell Ca 2+ channel current (I Ba ) in a dosedependent manner with an estimated IC 50 value of 167 nM. Block was incomplete and saturated at a maximal concentration of 25 mM. 5 Inhibition was signi®cantly decreased in the presence of the neutral amino acid L-isoleucine (25 mM) but unaected by application of the GABA B antagonist, saclofen (200 mM), suggesting a direct action on the a 2 d subunit of the Ca 2+ channel. 6 Gabapentin inhibition was voltage-dependent, producing an *7 mV hyperpolarizing shift in current voltage properties and reducing a non-inactivating component of whole-cell current activated at relatively depolarized potentials. 7 The use of speci®c Ca 2+ channel antagonists revealed a mixed pharmacology of the gabapentinsensitive current (N-, L-and P/Q-type), which is dominated by N-type current. 8 The present study is the ®rst to demonstrate that gabapentin directly mediates inhibition of voltage-gated Ca 2+ in¯ux in DRG neurones, providing a potential means for gabapentin to eectively mediate spinal anti-nociception.

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