The contributions of protein kinase A and protein kinase C to the actions of 5-HT on the L-type Ca2+ current of the sensory neurons in Aplysia.
In the sensory neurons of Aplysia, 5-HT acts through cAMP to reduce current flow through two classes of K+ channels, the S-K + channel and a transient K+ channel (Ikv). In addition, 5-HT increases a voltage-dependent, nifedipine-sensitive Ca2+ current. In this article we show that, while the effect on the S-K+ channel is mediated exclusively by cAMP, the effect on the Ca2+ current can be mimicked by phorbol 12,13-dibutyrate (PDBu) as well as by intracellular injection of cAMP. We then use specific blockers of protein kinase C (PKC) and the cAMP-dependent protein kinase A (PKA) to examine the roles of PKC and PKA in mediating the effect of 5-HT on the nifedipine-sensitive Ca2+ current. We find that H-7, a kinase inhibitor that appears to inhibit PKC more effectively than PKA in intact Aplysia neurons, reverses the increase in the Ca2+ current produced by PDBu. Moreover, H-7 partially blocks the effect of 5-HT on the Ca2+ current without affecting the decrease in the S-K+ current. A more specific PKC inhibitor (the 19-31 pseudosubstrate of PKC) also partially blocks the increase in the Ca2+ current produced by 5-HT, suggesting that this increase is mediated by PKC. Rp-cAMPS, a specific blocker of PKA, did not block the increase in the Ca2+ current produced by 5-HT, suggesting that the effect of 5-HT on this current may be mediated to only a small extent by PKA. The effect of 5-HT on the S-K+ current and the Ca2+ current can also be separated on basis of the time course of their appearance. The fact that the decrease in the S-K+ current precedes the increase in Ca2+ current suggests that there may be a temporal difference in the activation of the two kinase systems.
Braha
O
O
Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts 01545.
Edmonds
B
B
Sacktor
T
T
Kandel
E R
ER
Klein
M
M
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004594:Electrophysiology; D007546:Isoquinolines / Q000494:pharmacology; D009475:Neurons, Afferent / Q000187:drug effects* / Q000502:physiology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011188:Potassium / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D013997:Time Factors
D002121:Calcium Channel Blockers; D007546:Isoquinolines; D010879:Piperazines; D015221:Potassium Channels; D047428:Protein Kinase Inhibitors; D012701:Serotonin; D015240:Phorbol 12,13-Dibutyrate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D011494:Protein Kinases; D011493:Protein Kinase C; D011188:Potassium; D002118:Calcium