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Simultaneous recordings of presynaptic calcium currents and postsynaptic responses from the chick ciliary ganglion
S6
A VOLTAGE-DEPENDENT MODE OF Ca*+-INDUCED Ca*+ RELEASE IN CULTURED BULLFROG SYMPATHETIC NEURONES. KENJI KUBA, SHAO-YING HUA, AND MITSUO NOHMI, Department of Physiology, Saga Medical School, 5-1-l,,Nabeshima, Saga 849, Japan. It is still unknown whether CaL' is released from intracellular action potentials in neurones. Both a rise in the intracellular fluorescence changes with a sient: recorded as furainduced by a command voltage from -6OmV to OmV, looms, solution and not induced during a strong pulse to ;tOmV. siq:t, but not ICa, was partially blocked by ryanodine (50pM). Ca -transient/unit (estimated from the integral of ICa ) increased with an increase in Ca*+ Ca influ3+_ influx. Ca transient was facilitated when it was induced during the decy+ phase of the receding one, but, not in the presence of dantrolene (10pM). Ca -transient/Ca4+ influx was enhanced, as the voltage pulse amplitude was increased. X-t scanning of a cell with a conf cal microscope revealed that a command voltage produced the inward spread of Ca 5+ wave (seen by indo-l fluorescence), whose rate was initially fast in cytoplasm and then slow in the deeper regions. These results suggest -transients in cultured bullfro sympathetic neuro es result from not only Ca influx but also intracellular Ca 2+ release and that Ca ?+ release o2c+urs in a graded manner due to the voltage-dependent property of Ca*+ -induced Ca release mechanism (especially in the absence of activators, such as caffeine) and to a limited period of membrane depolarization.
SIMULTANEOUSRECORDINGSOFPRFSYNAPTIC CALCIIJMCHWENTSANDPOSTSYNAFTICRESPONSESF'R~THECHICK CILIAKYGANGLION. HIROMU YAWO, Departmentof Physiolopy,Kyoto UniversityFacultyof Medicine, Kyoto 606-01,Japan. A fluorescent dye, dextran-tetramethylrhodamine was applied to the cut end of the oculomotor nerve in chick embryos (stage 39-40).
The dye was transported orthogradely and accumulated in the
presynaptic terminals of the ciliary ganglion. identified nerve terminals.
Whole-cell recording were carried out from the
When postsynaptic responses were monitored simultaneously, an EPSP
(or EPSC) was elicited by activation of presynaptic calcium currents in the presence of TTX.
The diversity of presynaptic calcium channels was studied by barium as a charge carrier.
There was no evidence for the existence of low-threshold calcium channels in the presynaptic terminal.
The high-threshold barium currents showed no rapid inactivation.
A fraction of barium
currents was sensitive to both dihydropyridines and w-conotoxin, whereas a substantial fraction of the current was resistant to both agents.
Thus, the presynaptic terminal has at least two
subtypes of high-threshold calcium channel.
PRINCIPLE OF DENDRITIC ACTIVITIES
IN HIPPOCAMPAL PYRAMIDAL CELLS AND MOTONEURONS
YASUICHIRO FUJITA, Department of Physioloqv, Nippon Medical School, l-l-5, Sendagi, Bunkyo-ku, Tokyo, 113 Japan In CA1 Pyramidal cells the dendritic spike was 1.2-1.5 ms in duration and of low safety factor (the unitary D-spike), and in principle, it was by compansating
for the low safety factor through summation of unitary D-spikes that
made impulses conduct further forward in press).
(Fujita, Y., J. Physiol., London, 1991,
It was suggested that the safety factor could be increased by plastic
changes induced in the dendrites through learning
(ibid.).
These results were
further confirmed in CA3-CA4 pyramidal cells of rabbits and spinal motoneurons of cats anesthetized with Nembutal and immobilized with D-tubocurarine.
That is
to say, the unitary D-spike did occur in both types of neurons. A single unitary D-spike never gave rise to a full spike. Generation of a full spike through dendritic excitation as a rule entailed the summation of many unitary D-spikes.
A VOLTAGE-DEPENDENT MODE OF Ca*+-INDUCED Ca*+ RELEASE IN CULTURED BULLFROG SYMPATHETIC NEURONES. KENJI KUBA, SHAO-YING HUA, AND MITSUO NOHMI, Department of Physiology, Saga Medical School, 5-1-l,,Nabeshima, Saga 849, Japan. It is still unknown whether CaL' is released from intracellular action potentials in neurones. Both a rise in the intracellular fluorescence changes with a sient: recorded as furainduced by a command voltage from -6OmV to OmV, looms, solution and not induced during a strong pulse to ;tOmV. siq:t, but not ICa, was partially blocked by ryanodine (50pM). Ca -transient/unit (estimated from the integral of ICa ) increased with an increase in Ca*+ Ca influ3+_ influx. Ca transient was facilitated when it was induced during the decy+ phase of the receding one, but, not in the presence of dantrolene (10pM). Ca -transient/Ca4+ influx was enhanced, as the voltage pulse amplitude was increased. X-t scanning of a cell with a conf cal microscope revealed that a command voltage produced the inward spread of Ca 5+ wave (seen by indo-l fluorescence), whose rate was initially fast in cytoplasm and then slow in the deeper regions. These results suggest -transients in cultured bullfro sympathetic neuro es result from not only Ca influx but also intracellular Ca 2+ release and that Ca ?+ release o2c+urs in a graded manner due to the voltage-dependent property of Ca*+ -induced Ca release mechanism (especially in the absence of activators, such as caffeine) and to a limited period of membrane depolarization.
SIMULTANEOUSRECORDINGSOFPRFSYNAPTIC CALCIIJMCHWENTSANDPOSTSYNAFTICRESPONSESF'R~THECHICK CILIAKYGANGLION. HIROMU YAWO, Departmentof Physiolopy,Kyoto UniversityFacultyof Medicine, Kyoto 606-01,Japan. A fluorescent dye, dextran-tetramethylrhodamine was applied to the cut end of the oculomotor nerve in chick embryos (stage 39-40).
The dye was transported orthogradely and accumulated in the
presynaptic terminals of the ciliary ganglion. identified nerve terminals.
Whole-cell recording were carried out from the
When postsynaptic responses were monitored simultaneously, an EPSP
(or EPSC) was elicited by activation of presynaptic calcium currents in the presence of TTX.
The diversity of presynaptic calcium channels was studied by barium as a charge carrier.
There was no evidence for the existence of low-threshold calcium channels in the presynaptic terminal.
The high-threshold barium currents showed no rapid inactivation.
A fraction of barium
currents was sensitive to both dihydropyridines and w-conotoxin, whereas a substantial fraction of the current was resistant to both agents.
Thus, the presynaptic terminal has at least two
subtypes of high-threshold calcium channel.
PRINCIPLE OF DENDRITIC ACTIVITIES
IN HIPPOCAMPAL PYRAMIDAL CELLS AND MOTONEURONS
YASUICHIRO FUJITA, Department of Physioloqv, Nippon Medical School, l-l-5, Sendagi, Bunkyo-ku, Tokyo, 113 Japan In CA1 Pyramidal cells the dendritic spike was 1.2-1.5 ms in duration and of low safety factor (the unitary D-spike), and in principle, it was by compansating
for the low safety factor through summation of unitary D-spikes that
made impulses conduct further forward in press).
(Fujita, Y., J. Physiol., London, 1991,
It was suggested that the safety factor could be increased by plastic
changes induced in the dendrites through learning
(ibid.).
These results were
further confirmed in CA3-CA4 pyramidal cells of rabbits and spinal motoneurons of cats anesthetized with Nembutal and immobilized with D-tubocurarine.
That is
to say, the unitary D-spike did occur in both types of neurons. A single unitary D-spike never gave rise to a full spike. Generation of a full spike through dendritic excitation as a rule entailed the summation of many unitary D-spikes.