Expression of Ca2+ channel subunits during cardiac ontogeny in mice and rats: Identification of fetal ?1C and ? subunit isoforms

Abstract

Functional cardiac L-type calcium channels are composed of the pore-forming alpha(1C) subunit and the regulatory beta(2) and alpha(2)/delta subunits. To investigate possible developmental changes in calcium channel composition, we examined the temporal expression pattern of alpha(1C) and beta(2) subunits during cardiac ontogeny in mice and rats, using sequence-specific antibodies. Fetal and neonatal hearts showed two size forms of alpha(1C) with 250 and 220 kDa. Quantitative immunoblotting revealed that the rat cardiac 250-kDa alpha(1C) subunit increased about 10-fold from fetal days 12-20 and declined during postnatal maturation, while the 220-kDa alpha(1C) decreased to undetectable levels. The expression profile of the 85-kDa beta(2) subunit was completely different: beta(2) was not detected at fetal day 12, rose in the neonatal stage, and persisted during maturation. Additional beta(2)-stained bands of 100 and 90 kDa were detected in fetal and newborn hearts, suggesting the transient expression of beta(2) subunit variants. Furthermore, two fetal proteins with beta(4) immunoreactivity were identified in rat hearts that declined during prenatal development. In the fetal rat heart, beta(4) gene expression was confirmed by RT-PCR. Cardiac and brain beta(4) mRNA shared the 3 prime region, predicting identical primary sequences between amino acid residues 62-519, diverging however, at the 5 prime portion. The data indicate differential developmental changes in the expression of Ca(2+) channel subunits and suggest a role of fetal alpha(1C) and beta isoforms in the assembly of Ca(2+) channels in immature cardiomyocytes.

Identification and expression of voltage‐gated calcium channel β subunits in Zebrafish

“…We detected a high level of cacnb4b transcript in the cerebellum in accordance with a role for CACNB4b in regulating motor behaviors. The ␤4 subunit is also expressed by the fetal heart in rats and precedes expression of the ␤2 subunit (Haase et al, 2000). Similarly in zebrafish cacnb4a was expressed by the embryonic heart during 24 -72 hpf when neither cacnb2a nor cacnb2b expression was detected.…”

“…␤2 is the predominant ␤ subunit in the heart and targeted knockout of ␤2 results in prenatal death due to cardiac failure in mice (Ball et al, 2002). During embryonic development of the rat, however, ␤2 subunit in not detected in the heart until fetal day 15 and its abundance increases steadily with the maturation of the heart until birth (Haase et al, 2000). Similarly, as assayed by in situ hybridization expression of neither cacnb2a nor cacnb2b was detected in the developing cardiac tissue during the earliest stages of heart development in zebrafish.…”

“…CACNB4 is essential for the function of neural circuits controlling motor behaviors because it is mutated in mouse lethargic mutants that exhibit an epilepsy-like phenotype (Burgess et al, 1997;Haase et al, 2000). Both zebrafish CACNB4 homologs are expressed widely in brain, consistent with the neural function of CACNB4.…”

“…In excitable cells, such as muscles, neurons and endocrine cells, voltage-gated calcium channels play important roles in a variety of processes, including excitation-contraction coupling, synaptic transmission, and hormone secretion (Sheng et al, 1994;Rettig et al, 1997;Schredelseker et al, 2005). In addition, Ca 2ϩ entering through voltagegated calcium channels can serve as a second messenger in signaling pathways to regulate gene expression in developmental processes, including mesoderm patterning, neural induction, process outgrowth, neuronal migration, and cardiac cell differentiation (Komuro and Rakic, 1992;Moorman and Hume, 1993;Moreau et al, 1994;Leclerc et al, 1995Leclerc et al, , 1997Leclerc et al, , 2000Brosenitsch et al, 1998;Haase et al, 2000;Palma et al, 2001;Rottbauer et al, 2001).…”

Diversity and Developmental Expression of L-type Calcium Channel β2 Proteins and Their Influence on Calcium Current in Murine Heart

“…In heart, the principal CaV␣ 1 subunit, CaV␣ 1 c (CaV1.2), is encoded by the Cacna1C gene (5). Four genes (Cacnb1-4) encoding CaV␤ subunits have been identified that are expressed in the heart of different species including human, rabbit, and rat (6,7,8).…”