Effect of hypericin on the activity of protein kinase C in cultured human retinal pigment epithelial cells in vitro / 中华眼底病杂志

Objective To investigate the effect of hypericin on the activity of protein kinase C (PKC) in cultured human retinal pigment epithelium (RPE) cells in vitro. Methods RPE cells were cultured in standard medium with 10% serum concentrations containing 0.5 to 5.0 ?mol/L hypericin with or without preincubation of phorbol 12 myristate 13 acetate (PMA). The activities of cytosolic PKC (c PKC) and membranous PKC (m PKC) were assayed by PKC kit. Results The original activities of c PKC and m PKC of RPE cells were (35.34?4.10) pmol?min 1 ?mg 1 and (62.52?8.80) pmol?min 1 ?mg 1 . The activity of c PKC in RPE cells with PMA preincubation decreased rapidly in 5 minutes, with a subsequent slow decrease after 20 minutes and a decrease to 18% of the activity of c PKC in RPE cells without PMA preinubation after 60 minutes. While the activity of m PKC in RPE cells with PMA preincubation increased gradually after 5 minutes and reduced after reached the peak at 40 minutes, and then returned to baseline after 60 minutes, eventually decreased below 30% of the control group. When RPE cells were cultured with PMA for 48 hours, the activities of c PKC and m PKC were hardly detectable, while RPE cells were cultured with both PMA and hypericin, hypericin could counteract most of down regulation by PMA. Conclusion Hypericin may inhibit the translocation of PKC in RPE cells,change the activity of PKC, promote the apoptosis of RPE cells likely,and then prevent proliferative vitreoretinopathy.

A Study on the Role of Protein Kinase C upon the Acetylcholine Release in the Rat Hippocampus

The effects and interactions of 4 beta-phorbol 12,13-dibutyrate(PDB) and polymyxin B(PMB) with adenosine on the electrically-evoked acetylcholine(ACh) release were studied in rat hippocampus. Slices from rat hippocampus were equilibrated with 3H-choline and the release of the labeled product, 3H-ACh, which was evoked by electrical stimulation(3Hz, 2ms, 5Vcm-1, rectangular pulses) was measured. PDB(0.3-10 micorM), a selective protein kinase C(PKC) activator, increased the evoked ACh release in a dose related fashion with an increase in the basal rate of release. The effects of 1(M PDB were significantly inhibited by 0.3 micorM tetrodotoxin(TTX) pretreatment or Ca++-free medium. PMB(0.03-1mg), a selective PKC inhibitor, decreased the ACh release in a dose dependent manner with an increase in the basal rate of release. Adenosine(1-10 micorM) decreased the ACh release without changing the basal rate or release, and this effect was significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine(2 micorM), a selective A1-receptor antagonist treatment. However, adenosine effects were not affected by PDB and PMB. These results indicate that the PKC play a role in the ACh release in the rat hippocampus but is not involved in the post-receptor mechanism of the A1-adenosine receptor.