Polymerase chain reaction cloning of L-type calcium channel sequences from the heart and the brain

The impact of splice isoforms on voltage-gated calcium channel alpha1 subunits

Semi-conserved exon boundaries in members of the CACNA1 gene family result in recurring pre-mRNA splicing patterns. The resulting variations in the encoded pore-forming subunit of the voltage-gated calcium channel affect functionally significant regions, such as the vicinity of the voltage-sensing S4 segments or the intracellular loops that are important for protein interaction. In addition to generating functional diversity, RNA splicing regulates the quantitative expression of other splice isoforms of the same gene by producing transcripts with premature stop codons which encode two-domain or three-domain channels. An overview of some of the known splice isoforms of the alpha(1) calcium channel subunits and their significance is given.

Calcium antagonists and vasodilatation

Calcium antagonists comprise a diverse group of chemically unrelated agents that interact with voltage-operated calcium channels (L-type) and thereby inhibit smooth muscle contractility. They are used to treat several major cardiovascular disorders, including hypertension and angina pectoris; they are also studied in congestive heart failure and in atherosclerosis. The current view is that their therapeutic action is related to vasodilatation. This view is an oversimplification, as will be shown in this review. It will also be illustrated that all calcium antagonists are not identical pharmacological agents.

Ca2+ channels: diversity of form and function

The past year has seen some significant advances in our understanding of the structural and functional properties of neuronal voltage-gated Ca2+ channels. Molecular cloning and protein purification studies have identified structural components, and expression studies are beginning to define the biophysical and pharmacological properties of the cloned channels. A number of studies of native Ca2+ channels show that the concept of channel modulation includes gating by both voltage and ligands.

Tissue-specific expression of high-voltage-activated dihydropyridine-sensitive L-type calcium channels

The cloning of the cDNA for the alpha 1 subunit of L-type calcium channels revealed that at least two genes (CaCh1 and CaCh2) exist which give rise to several splice variants. The expression of mRNA for these alpha 1 subunits and the skeletal muscle alpha 2/delta, beta and gamma subunits was studied in rabbit tissues and BC3H1 cells. Nucleic-acid-hybridization studies showed that the mRNA of all subunits are expressed in skeletal muscle, brain, heart and aorta. However, the alpha 1-, beta- and gamma-specific transcripts had different sizes in these tissues. Smooth muscle and heart contain different splice variants of the CaCh2 gene. The alpha 1, beta and gamma mRNA are expressed together in differentiated but not in proliferating BC3H1 cells. A probe specific for the skeletal muscle alpha 2/delta subunit did not hybridize to poly(A)-rich RNA from BC3H1 cells. These results suggest that different splice variants of the genes for the alpha 1, beta and gamma subunits exist in tissues containing L-type calcium channels, and that their expression is regulated in a coordinate manner.