| Summary: | 碩士 === 國立臺灣大學 === 藥理學研究所 === 92 === The roles of phosphodiesterase (PDE) on the spontaneous action potentials and the effects of phosphodiesterase (PDE) inhibitors on bursts of potential elicited by d-amphetamine were studied on RP4 neuron of snail, Achatina fulica Ferussac in vitro. PDE inhibitors used include: vinpocetine (PDE1 selective), erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA, PDE2 selective), milrinone (PDE3 selective), rolipram (PDE4 selective), sildenafil (viagra) (PDE5 selective) and the non-selective inhibitor, caffeine. Vinpocetine, EHNA, milrinone, rolipram and caffeine but not sildenafil (viagra), did elicited bursts of potentials on the RP4 neuron. Calcium free solution or high magnesium solution or U73122 did not block the bursts of potential elicited by rolipram. However, the bursts of potential elicited by rolipram were blocked by KT5720. Similar effects were also found in vinpocetine, EHNA, milrinone and caffeine elicited bursts of potential. These results suggest that vinpocetine, EHNA, milrinone, rolipram or caffeine elicited bursts of potential through cAMP signalling pathways in central neuron of snail.
The ionic currents of the RP4 neuron were measured under two electrode voltage clamping. Rolipram significantly decreased the amplitude of total inward currents and outward currents in a concentration-dependent manner, but did not elicit a negative slope resistance (NSR) in current-voltage relationships of steady-state outward currents. These results suggest that the effect was in associate with the phosphodiesterase activity in the neuron. It is concluded that the phosphodiesterase activity plays an important role on the modulation of potentials in the RP4 neuron.
Oscillation of membrane potential and bursts of potential were elicited by d-amphetamine, vinpocetine, EHNA, milrinone, rolipram and caffeine in a concentration-dependent manner, while sildenafil (viagra) did not elicit bursts of potential on the RP4 neurons. Caffeine (10 mM), vinpocetine (160 μM), EHNA (300 μM), milrinone (100 μM), rolipram (100 μM) and forskolin (100 μM) potentiate the bursts of potential elicited by d-amphetamine. Sildenafil (Viagra, 1 mM) did not affect the bursts of potentials elicited by d-amphetamine. It is concluded that the bursts of potential elicited by d-amphetamine was associated with the phosphodiesterase activity in the neuron.
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