Distribution and translocation of isoforms of protein kinase C in rat submandibular acinar cells

The distribution of six isoforms of protein kinase C (PKC) in seromucous acinar cells of rat submandibular gland was examined and their translocation from the cytosolic- to the membrane fraction after different stimuli investigated. Western blotting, immunostaining with isoform-specific antibodies and scanning densitometry showed that PKC-α and ϵ were distributed fairly evenly between the cytosol and membranes in resting cells, while isoforms- β, δ and ζ were all predominantly localized (over 80%) in membranes. PKC-γ was not detected. PKC-α was mobilized to the membrane fraction by the phorbol ester, TPA, but not by the phosphoinositide-coupled agonists carbachol, methoxamine and substance P (SP). PKC-ϵ was translocated by TPA and carbachol but not by SP or methoxamine. Biochemical assay of total PKC confirmed that cytosolic enzyme activity was significantly reduced by TPA and carbachol to 29% and 75% respectively of control levels. These results suggest that muscarinic regulation of the mucosecretory response in the rat submandibular gland may be mediated by the PKC-ϵ isoform.