Depressing effects of protein kinases A & C on the receptor- induced K+-current responses in the ganglion cells of Aplysia
Sasaki, K.; Matsumoto, G.; Takashima, K.; Fujita, R.; Kawasaki, K.; Kimura, D.K.; Sato, M. (1994). Depressing effects of protein kinases A & C on the receptor- induced K+-current responses in the ganglion cells of Aplysia. Neth. J. Zool. 44(3-4): 578-587
In: Netherlands Journal of Zoology. E.J. Brill: Leiden. ISSN 0028-2960; e-ISSN 1568-542X, more
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| Authors | | Top |
- Sasaki, K.
- Matsumoto, G.
- Takashima, K.
- Fujita, R.
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- Kawasaki, K.
- Kimura, D.K.
- Sato, M.
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| Abstract |
Application of either dopamine (DA), acetylcholine (ACh), histamine (Ha), or Phe-Met-Arg-Phe-NH2 (FMRFamide) induces a K+-current response in the ganglion cells of Aplysia under voltage clamp. We have previously reported that these responses are all mediated by a pertussis toxin (PTX)-sensitive G-protein Gi or Go. Intracellular application of cAMP, an activator of protein kinase A (PKA), or extracellular application of 30 µM phorbol dibutyrate (PDBu), an activator of protein kinase C (PKC), markedly suppressed these transmitter-induced K+-current responses. The depressing effect of cAMP was reversible while that of PDBu irreversible as observed for 1 hour. Intracellular injection of okadaic acid (OA), an inhibitor phosphatases, facilitated the blocking effects of both cAMP and PDBu. The dose-response curve obtained by each transmitter-receptor system shifted downward by application of either cAMP or PDBu without affecting the affinity of the agonist to each receptor. K+-channel opening directly induced by guanosine thiotriphosphate (GTPgammaS) or by raising the temperature was not depressed y either cAMP or 100 µM PDBu. From these results, we postulated that the acting sites of both PKA and PKC might be somewhere between the receptors and G-protein, and that the phosphorylation of these sites would the functional coupling efficiency between the receptors and G-protein. |
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