Calcium channel β subunit heterogeneity: Functional expression of cloned cDNA from heart, aorta and brain

Complemetary DNAs encoding three novel and distinct β subunits (CaB2a, CaB2b and CaB3) of the high voltage activated (L-type) calcium channel have been isolated from rabbit heart. Their deduced amino acid sequence is homologous to the β subunit originally cloned from skeletal muscle (CaB1). CaB2a and CaB2b are splicing products of a common primary transcript (CaB2). Northern analysis and specific amplification of CaB2 and CaB3 specific cDNAs by polymerase chain reactions showed that CaB2 is predominantly expressed in heart, aorta and brain, whereas CaB3 is most abundant in brain but also present in aorta, trachea, lung, heart and skeletal muscle. A partial DNA sequence complementary to a third variant of the CaB2 gene, subtype CaB2c, has also been cloned from rabbit brain. Coexpression of CaB2a, CaB2b and CaB3 with α1heart enhances not only the expression in the oocyte of the channel directed by the cardiac α1 subunit alone, but also effects its macroscopic characteristics such as drug sensitivity and kinetics. These results together with the known α1 subunit heterogeneity, suggest that different types of calcium currents may depend on channel subunit composition.