EXPRESSION OF AN ACIDIC ISOFORM OF CALPONIN IN RAT-BRAIN - WESTERN BLOTS ON ONE-DIMENSIONAL OR 2-DIMENSIONAL GELS AND IMMUNOLOCALIZATION INCULTURED-CELLS

Calponin, an actin- and Ca2+-calmodulin-binding protein characterized as an inhibitory factor of the smooth-muscle actomyosin activity, has also been shown to be present in some non-muscle cells. However, there is a controversy as to whether calponin is present or not in brain. S everal laboratories indicate that this protein is absent in chicken or bovine brains, while Applegate et al. [Applegate, Feng, Green and Tau bman (1994) J. Biol. Chem. 269, 10683-10690] have recently reported th e identification of an mRNA specific for a 36 kDa non-muscle calponin analogue in homogenates of rat brains. For the first time we demonstra te, by Western blots and in situ immunofluorescence localization using monoclonal as well as affinity-purified polyclonal antibody to gizzar d calponin, that a 36-37 kDa and a 35-36 kDa calponin-like proteins ar e expressed respectively in pig and rat brains and in rat cerebellar c ultured cells. The acidic pI (5.2-5.4) of the rat brain protein reveal ed by isoelectric focusing is in good agreement with that of the prote in coded for by the calponin isoform mRNA described by Applegate et al . and is different from that of the protein from chicken gizzard (pI 9 .9). Brain calponin-like protein is different from two other Ca2+-calm odulin-binding proteins previously identified in brain, namely caldesm on and adducin, and from tropomyosin.