Heterologous expression studies have shown that the activity of voltage-gated Ca 2؉ channels is regulated by their ␤ subunits in a ␤ subunit isoform-specific manner. In this study we therefore investigated if one or several ␤ subunit isoforms associate with L-type Ca 2؉ channels in different regions of mammalian brain.All four ␤ subunit isoforms (␤1b, ␤2, ␤3, and ␤4) are expressed in cerebral cortex as shown in immunoblots. Immunoprecipitation of (؉)-[3 H]isradipine-labeled Ltype channels revealed that the majority of ␤ subunitassociated L-type channels was associated with ␤3 (42 ؎ 8%) and ␤4 (42 ؎ 7%) subunits, whereas ␤1b and ␤2 were present in a smaller fraction of channel complexes. ␤3 and ␤4 were also the major L-type channel ␤ subunits in hippocampus. In cerebellum ␤1b, ␤2, and ␤3 but not ␤4 subunits were expressed at lower levels than in cortex. Accordingly, ␤4 was the most prominent ␤ subunit in cerebellar L-type channels. This ␤ subunit composition was very similar to the one determined for 125 I--conotoxin-GVIA-labeled N-type and 125 I--conotoxin-MVIIClabeled P/Q-type channel complexes in cerebral cortex and cerebellum.Our data show that all four ␤ subunit isoforms associate with L-type Ca 2؉ channels in mammalian brain. This ␤ subunit heterogeneity may play an important role for the fine tuning of L-type channel function and modulation in neurons.Voltage-gated Ca 2ϩ channels control the depolarization-induced influx of extracellular Ca 2ϩ into neurons and other electrically excitable cells. They exist as hetero-oligomeric complexes of different subunits (␣1, ␣2-␦, and ␤). Different types of neuronal Ca 2ϩ channels (termed L-, N-, P-, Q-, and R-type; 1) are discriminated by biophysical and pharmacological criteria (for reviews see Refs. 2-5). N-and P/Q-type channels are blocked by peptide toxins (-CTx

Within-species variation in genome size has been documented in many animals and plants. Despite its importance for understanding eukaryotic genome diversity, there is only sparse knowledge about how individual-level processes mediate genome size variation in populations. Here we study a natural population of the rotifer Brachionus asplanchnoidis whose members differ up to 1.9-fold in diploid genome size, but were still able to interbreed and produce viable offspring. We show that genome size is highly heritable and can be artificially selected up or down, but not below a certain basal diploid genome size for this species. Analyses of segregation patterns in haploid males reveal that large genomic elements (several megabases in size) provide the substrate of genome size variation. These elements, and their segregation patterns, explain the generation of new genome size variants, the short-term evolutionary potential of genome size change in populations, and some seemingly paradoxical patterns, like an increase in genome size variation among highly inbred lines. Our study suggests that a conceptual model involving only two variables, (1) a basal genome size of the population, and (2) a vector containing information on additional elements that may increase genome size in this population (size, number, and meiotic segregation behaviour), can effectively address most scenarios of short-term evolutionary change of genome size in a population.

Aminoglycoside antibiotics can cause neuromuscular block by inhibiting Ca2+ influx into motor nerve terminals. P/Q-type Ca2+ channels, which are formed by alpha 1A subunits, are mainly responsible for depolarization-dependent presynaptic Ca2+ entry in motor neurons. We therefore investigated the possibility that aminoglycosides function as P/Q-type channel blockers. They inhibited [125I]-omega-CTx-MVIIC binding to P/Q-type channels in guinea pig cerebellum membranes with nanomolar IC50 values (e.g., 8 nM for neomycin). Divalent cations decreased the apparent affinity of neomycin. Barium inward currents through alpha 1A subunits expressed in Xenopus oocytes were partially blocked by therapeutic concentrations of aminoglycosides. This explains that therapeutically relevant concentrations of these drugs decrease the reserve of neuromuscular transmission, which can lead to neuromuscular block. We conclude that micromolar concentrations of aminoglycosides block not only N-type but also P/Q-type channels in mammalian neurons.

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Sex-specific markers are a prerequisite for understanding reproductive biology, genetic factors involved in sex differences, mechanisms of sex determination, and ultimately the evolution of sex chromosomes. The Western mosquitofish, Gambusia affinis, may be considered a model species for sex-chromosome evolution, as it displays female heterogamety (ZW/ZZ), and is also ecologically interesting as a worldwide invasive species. Here, de novo RNA-sequencing on the gonads of sexually mature G. affinis was used to identify contigs that were highly transcribed in females but not in males (i.e., transcripts with ovary-specific expression). Subsequently, 129 primer pairs spanning 79 contigs were tested by PCR to identify sex-specific transcripts. Of those primer pairs, one female-specific DNA marker was identified, Sanger sequenced and subsequently validated in 115 fish. Sequence analyses revealed a high similarity between the identified sex-specific marker and the 3´ UTR of the aminomethyl transferase (amt) gene of the closely related platyfish (Xiphophorus maculatus). This is the first time that RNA-seq has been used to successfully characterize a sex-specific marker in a fish species in the absence of a genome map. Additionally, the identified sex-specific marker represents one of only a handful of such markers in fishes.