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The [beta] subunits of voltage-gated [Ca.sup.2+] channels are known to be regulators of the channels' gating properties. Here we report a striking additional function of a [beta] subunit. Screening of chicken cochlear and brain cDNA libraries identified [[beta].sub.4c], a short splice variant of the [[beta].sub.4] subunit. Although [[beta].sub.4c] occurs together with the longer isoforms [[beta].sub.4a] or [[beta].sub.4b] in the brain, eye, heart, and lung, the cochlea expresses exclusively [[beta].sub.4c]. The association of [[beta].sub.4c] with the [Ca.sup.2+]-channel [[alpha].sub.1] subunit has slight but significant effects on the kinetics of channel activation and inactivation. Yeast two-hybrid and biochemical assays revealed that [[beta].sub.4c] interacts directly with the chromo shadow domain of chromobox protein 2/heterochromatin protein 1[gamma] (CHCB2/HP1[gamma]), a nuclear protein involved in gene silencing and transcriptional regulation. Coexpression of this protein specifically recruits [[beta].sub.4c] to the nuclei of mammalian cells. Furthermore, [[beta].sub.4c] but not [[beta].sub.4a] dramatically attenuates the gene-silencing activity of chromobox protein 2/heterochromatin protein 1[gamma]. The [[beta].sub.4c] subunit is therefore a multifunctional protein that not only constitutes a portion of the [Ca.sup.2+] channel but also regulates gene transcription.

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RGK (Rad-Gem-Rem) GTPases have been described as potent negative regulators of the Ca2+ influx via high-threshold voltage-activated Ca2+ channels. Recent work, mostly performed on Cav1.2 Ca2+ channels, has highlighted the crucial role played by the channel auxiliary Cavβ subunits and identified several GTPase and β-subunit protein domains involved in this regulation. We now extend these conclusions by producing the first complete characterization of the effects of Gem, Rem, and Rem2 on the neuronal Cav2.1 Ca2+ channels expressed with Cavβ1 or Cavβ2 subunits. Current inhibition is limited to a decrease in amplitude with no modification in the voltage dependence or kinetics of the current. We demonstrate that this inhibition can occur for Cavβ constructs with impaired capacity to induce current potentiation, but that it is lost for Cavβ constructs deleted for their β-interaction domain. The RGK C-terminal last ~80 amino acids are sufficient to allow potent current inhibition and in vivo β-subunit/Gem interaction. Interestingly, although Gem and Gem carboxy-terminus induce a completely different pattern of β-subunit cellular localization, they both potently inhibit Cav2.1 channels. These data therefore set the status of neuronal Cav2.1 Ca2+ channel inhibition by RGK GTPases, emphasizing the role of short amino acid sequences of both proteins in β-subunit binding and channel inhibition and revealing a new mechanism for channel inhibition. [ABSTRACT FROM AUTHOR]

This article provides a first person narrative of the author's experiences with bullfighting in Spain.

Starting from a comparative study of different Ca2+ chelators on the G-protein-induced inhibition of the CaV2.1 Ca channels, we demonstrate that BAPTA and DM-nitrophen are able to interact, in a Ca2+- and lipid-dependent manner, with phospholipid monolayers. Critical insertion pressure and sensitivity to charged lipids indicated that insertion in the lipid film may occur in biological membranes as those found on Xenopus oocytes. This novel property is not found for EGTA and EDTA and may participate to the unusual ability of BAPTA-related molecules to chelate Ca2+ ions in the very close vicinity of the plasma membrane, where most of the Ca2+-dependent signalling triggered by voltage-gated Ca2+ currents occurs. [Copyright &y& Elsevier]

The β subunits of voltage-gated Ca[sup 2+] channels are known to be regulators of the channels' gating properties. Here we report a striking additional function of a β subunit. Screening of chicken cochlear and brain cDNA libraries identified β[sub 4c], a short splice variant of the β[sub 4] subunit. Although β[sub 4c] occurs together with the longer isoforms β[sub 4a] or β[sub 4b] in the brain, eye, heart, and lung, the cochlea expresses exclusively β[sub 4c]. The association of β[sub 4c] with the Ca[sup 2+]-channel α[sub 1] subunit has slight but significant effects on the kinetics of channel activation and inactivation. Yeast two-hybrid and biochemical assays revealed that β[sub 4c] interacts directly with the chromo shadow domain of chromobox protein 2/heterochromatin protein 1γ, (CHCB2/HP1γ), a nuclear protein involved in gene silencing and transcriptional regulation. Coexpression of this protein specifically recruits β[sub 4c] to the nuclei of mammalian cells. Furthermore, β[sub 4c] but not β[sub 4a] dramatically attenuates the genesilencing activity of chromobox protein 2/heterochromatin protein 1γ. The β[sub 4c] subunit is therefore a multifunctional protein that not only constitutes a portion of the Ca[sup 2+] channel but also regulates gene transcription. [ABSTRACT FROM AUTHOR]