Abstract
Voltage-gated Ca2+ channels in vertebrates comprise at least seven molecular subtypes, each of which produces a current with distinct kinetics and pharmacology. Although several invertebrate Ca2+ channel alpha1 subunits have also been cloned, their functional characteristics remain unclear, as heterologous expression of a full-length invertebrate channel has not previously been reported. We have cloned a cDNA encoding the alpha1 subunit of a voltage-gated Ca2+ channel from the scyphozoan jellyfish Cyanea capillata, one of the earliest existing organisms to possess neural and muscle tissue. The deduced amino acid sequence of this subunit, named CyCaalpha1, is more similar to vertebrate L-type channels (alpha1S, alpha1C, and alpha1D) than to non-L-type channels (alpha1A, alpha1B, and alpha1E) or low voltage-activated channels (alpha1G). Expression of CyCaalpha1 in Xenopus oocytes produces a high voltage-activated Ca2+ current that, unlike vertebrate L-type currents, is only weakly sensitive to 1,4-dihydropyridine or phenylalkylamine Ca2+ channel blockers and is not potentiated by the agonist S(-)-BayK 8644. In addition, the channel is less permeable to Ba2+ than to Ca2+ and is more permeable to Sr2+. CyCaalpha1 thus represents an ancestral L-type alpha1 subunit with significant functional differences from mammalian L-type channels.
Highlights
Voltage-gated Ca2ϩ channels are essential for coupling the depolarization of excitable cells to Ca2ϩ influx across the plasma membrane, leading to initiation of second messenger cascades and other intracellular events
We report here the cloning and functional expression of CyCa␣1, a voltage-gated Ca2ϩ channel ␣1 subunit from Cyanea
CyCa␣1 has the molecular structure of an L-type channel ␣1 subunit, certain aspects of the pharmacology and physiology of the expressed channel distinguish it from mammalian L-type channels
Summary
Voltage-gated Ca2ϩ channels are essential for coupling the depolarization of excitable cells to Ca2ϩ influx across the plasma membrane, leading to initiation of second messenger cascades and other intracellular events. We report here the cloning and functional expression of CyCa␣1, a voltage-gated Ca2ϩ channel ␣1 subunit from Cyanea. Primary Structure of the Cyanea Ca2ϩ Channel—The initial fragment of CyCa␣1 was isolated using two degenerate oligonucleotide primers corresponding to regions that are highly conserved in all known Ca2ϩ channel ␣1 subunits.
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