CHRONIC STIMULATION DIFFERENTIALLY MODULATES EXPRESSION OF MESSENGER-RNA FOR DIHYDROPYRIDINE RECEPTOR ISOFORMS IN RAT FAST-TWITCH SKELETAL-MUSCLE

This study examined the effects of low frequency chronic stimulation o n expression of the mRNA encoding the two isoforms of the alpha 1 subu nit of the dihydropyridine receptor (DHPR) calcium channel, a critical component of skeletal muscle excitation-contraction coupling. RNase p rotection assay was used to determine alteration in isoform expression in 5-day, 9-day and 13-day chronically stimulated rat tibialis anteri or muscle, and to compare it with soleus and extensor digitorum longus muscles. Low frequency chronic stimulation was associated not only wi th a significant decrease in the mRNA level of the skeletal isoform of the DHPR, but also with a significant increase in the mRNA level of t he cardiac isoform of the DHPR, the overwhelming majority of which was the adult splice variant. Significant levels of cardiac DHPR mRNA exp ression were also found in normal adult slow twitch soleus muscle, The se findings raise the question of a potential role for the cardiac DHP R in certain adult skeletal muscles. (C) 1997 Academic Press.