Action potential bursts in central snail neurons elicited by paeonol: roles of ionic currents.
OBJECTIVE
to investigate the effects of 2'-hydroxy-4'-methoxyacetophenone (paeonol) on the electrophysiological behavior of a central neuron (right parietal 4; RP4) of the giant African snail (Achatina fulica Ferussac).


METHODS
intracellular recordings and the two-electrode voltage clamp method were used to study the effects of paeonol on the RP4 neuron.


RESULTS
the RP4 neuron generated spontaneous action potentials. Bath application of paeonol at a concentration of ≥ 500 micromol/L reversibly elicited action potential bursts in a concentration-dependent manner. Immersing the neurons in Co(2+)-substituted Ca(2+)-free solution did not block paeonol-elicited bursting. Pretreatment with the protein kinase A (PKA) inhibitor KT-5720 or the protein kinase C (PKC) inhibitor Ro 31-8220 did not affect the action potential bursts. Voltage-clamp studies revealed that paeonol at a concentration of 500 micromol/L had no remarkable effects on the total inward currents, whereas paeonol decreased the delayed rectifying K(+) current (I(KD)) and the fast-inactivating K(+) current (I(A)). Application of 4-aminopyridine (4-AP 5 mmol/L), an inhibitor of I(A), or charybdotoxin 250 nmol/L, an inhibitor of the Ca(2+)-activated K(+) current (I(K(Ca))), failed to elicit action potential bursts, whereas tetraethylammonium chloride (TEA 50 mmol/L), an I(KD) blocker, successfully elicited action potential bursts. At a lower concentration of 5 mmol/L, TEA facilitated the induction of action potential bursts elicited by paeonol.


CONCLUSIONS
paeonol elicited a bursting firing pattern of action potentials in the RP4 neuron and this activity relates closely to the inhibitory effects of paeonol on the I(KD).
Graduate Institute of Acupuncture Science, College of Chinese Medicine, China Medical University, Taichung, Taiwan, China.
Yi-hung
YH
CHEN
Pei-lin
PL
LIN
Hui-yu
HY
HSU
Ya-ting
YT
WU
Han-yin
HY
YANG
Dah-yuu
DY
LU
Shiang-suo
SS
HUANG
Ching-liang
CL
HSIEH
Jaung-geng
JG
LIN
D015761:4-Aminopyridine / Q000494:pharmacology; D000098:Acetophenones / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002118:Calcium / Q000502:physiology; D002227:Carbazoles / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D004553:Electric Conductivity; D007211:Indoles / Q000494:pharmacology; D007473:Ion Channels / Q000502:physiology*; D009424:Nervous System Physiological Phenomena; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000502:physiology; D011758:Pyrroles / Q000494:pharmacology; D011930:Reaction Time; D012908:Snails / Q000502:physiology*; D019789:Tetraethylammonium / Q000494:pharmacology
D000098:Acetophenones; D002227:Carbazoles; D007211:Indoles; D007473:Ion Channels; D011758:Pyrroles; D018999:Charybdotoxin; C013638:paeonol; C057416:KT 5720; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D011188:Potassium; D002118:Calcium; C064758:Ro 31-8220