Calcium channels regulate a wide range of cellular activities. Based on physiological and pharmacological evidence, diverse calcium channel types exist and are presumably derived from independent genes. The regulation of these calcium channel genes during normal development and their effects on other genes are poorly understood. This project utilizes naturally occurring mutations in the calcium channel genes of vertebrates to gain insights into the structure of calcium channels and the modifications in electrophysiological and cellular functions that ensue from the altered structures. Muscular dysgenesis (mdg) of mice is a mutation in the gene for the alpha 1 subunit of the skeletal muscle dihydropyridine (DHP) receptor and leads to loss of normal calcium channels and excitation-contraction coupling. However, dysgenic muscle does contain a low level of a mRNA hybridizable with DHP receptor alpha 1 cDNA and also expresses an unusual calcium current. Detailed molecular characterizations (via cDNA cloning) of this DHP receptor mRNA from dysgenic muscle will be carried out to obtain insights into the structural domains within the normal DHP receptor which give rise to its electrophysiological properties. Expression of the """"""""dysgenic mRNA"""""""" in heterologous systems and antisense RNA inhibition of expression in dysgenic myotubes will be used to establish definitively whether this mRNA encodes a novel calcium channel. The crooked neck dwarf (cn) chicken and the cardiomyopathic (cm) hamster are known to exhibit functional alterations in their calcium currents. These mutants strains will be investigated along similar molecular genetic lines to determine if the functional alterations arise from mutations in the calcium channel genes in these mutants also. Finally, the effects of the DHP receptor on the accumulation of other mRNAs involved in muscle differentiation will be examined in normal myotubes developing under experimental paralysis in culture. These multi-disciplinary and collaborative studies will provide valuable new insights into the structure-function relationships, and the regulation, of calcium channel genes.
