ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Calcium-dependent phospholipid-sensitive protein kinase [protein kinase C (PKC)] was partially purified from the carp (Cyprinus carpio) retina through DE 52 ion exchange and Cellulofine gel filtration chromatography. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) activated PKC in the nanomolar range. A major 38-kDa protein in the retinal supernatants (105,000 g) was phosphorylated in vitro by PKC during a short period (3 min). Other phosphoproteins also appeared during a further prolonged period (〉15 min). Rod-bipolar and dopamine (DA) interplexiform cells in the fish retina were immunoreactive to a monoclonal antibody to PKC (α/β-subtype). The PKC antibody recognized a 78-kDa native PKC enzyme by means of an immunoblotting method. Subsequently, the effects of two kinds of PKC activators were investigated on [3H]DA release from retinal cell fractions containing DA cells that had been preloaded with [3H]DA. A phorbol ester (TPA) induced a calcium- and dose-dependent [3H]DA release during a short period (2 min), with the minimal effective dose being 1 nM. Other phorbols having no tumor-promoting activity, such as 4β-phorbol and 4α-phorbol 12, 13-didecanoate, were ineffective on [3H]DA release. A synthetic diacylglycerol [1-oleoyl-2-acetylglycerol (OAG)], which is an endogenous PKC activator, was also able to induce a significant release of [3H]DA. Furthermore, TPA was found to release endogenous DA from isolated fish retina by a highly sensitive HPLC with electrochemical detection method. The OAG- or TPA-induced [3H]DA or DA release was completely blocked by inhibitors of PKC, such as 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7) and staurosporine. In contrast, release of [3H]glycine, γ-[3H]aminobutyric acid, and D-[3H]aspartic acid was never induced by TPA. Taken together, the present data indicate that TPA or OAG triggers a release of DA synaptically and that the induction is due to a PKC activation specifically in the membrane of DA cells in the fish retina. The functional role of PKC in rod-bipolar cells is unknown at present.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1990.tb04914.x
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