Facilitatory and inhibitory transmitters modulate calcium influx during action potentials in aplysia sensory neurons.
Serotonin (5-HT) produces presynaptic facilitation and FMRFamide produces presynaptic inhibition in Aplysia sensory neurons. These effects may involve the modulation of Ca2+ influx into sensory neuron terminals during action potentials. Here, we have used the Ca2+ indicator dye fura-2 to monitor directly the effects of 5-HT and FMRFamide on internal Ca2+ concentration ([Ca2+]i). 5-HT caused a 50% increase in the transient rise in [Ca2+]i in response to action potentials, whereas FMRFamide decreased the [Ca2+]i transient by 40%. Neither transmitter altered the resting [Ca2+]i, the time course of recovery of the [Ca2+]i transient, or the [Ca2+]i transients produced by intracellular injection of CaCl2 or inositol 1,4,5-trisphosphate. We conclude that the effects of the transmitters on the action potential-induced [Ca2+]i transient are due to changes in Ca2+ influx and not in intracellular Ca2+ homeostasis.
Blumenfeld
H
H
Center for Neurobiology and Behavior, Howard Hughes Medical Institute, Columbia University, New York, New York 10032.
Spira
M E
ME
Kandel
E R
ER
Siegelbaum
S A
SA
D000200:Action Potentials; D000818:Animals; D001048:Aplysia; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D019835:FMRFamide; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D009475:Neurons, Afferent / Q000378:metabolism / Q000502:physiology*; D009479:Neuropeptides / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000502:physiology*; D009994:Osmolar Concentration; D012701:Serotonin / Q000494:pharmacology
D009479:Neuropeptides; D018377:Neurotransmitter Agents; D012701:Serotonin; D019835:FMRFamide; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium