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Biomedical subjects

Takayuki Murakoshi

Publications and source records attributed to Takayuki Murakoshi.

8 recordsLinked to original sources
PubMed2006

Altered cerebellar function in mice lacking CaV2.3 Ca2+ channel.

Voltage-dependent Ca(2+) channels play important roles in cerebellar functions including motor coordination and learning. Since abundant expression of Ca(V)2.3 Ca(2+) channel gene in the cerebellum was detected, we searched for possible deficits in the cerebellar functions in the Ca(V)2.3 mutant mice. Behavioral analysis detected in delayed motor learning in rotarod tests in mice heterozygous and homozygous for the Ca(V)2.3 gene disruption (Ca(V)2.3+/- and Ca(V)2.3-/-, respectively). Electrophysiological analysis of mutant mice revealed perplexing results: deficit in long-term depression (LTD) at the parallel fiber Purkinje cell synapse in Ca(V)2.3+/- mice but apparently normal LTD in Ca(V)2.3-/- mice. On the other hand, the number of spikes evoked by current injection in Purkinje cells under the current-clamp mode decreased in Ca(V)2.3 mutant mice in a gene dosage-dependent manner, suggesting that Ca(V)2.3 channel contributed to spike generation in Purkinje cells. Thus, Ca(V)2.3 channel seems to play some roles in cerebellar functions.

Action Potentials↗
PubMed2005

Metabotropic P2Y purinoceptor-mediated presynaptic and postsynaptic enhancement of cerebellar GABAergic transmission.

Cerebellar GABAergic inhibitory transmission is under heterosynaptic control mediated by diverse chemical messengers. Here, we investigated roles of metabotropic P2Y purinoceptors (P2YRs) on GABAergic synapses between cerebellar interneurons and Purkinje cells (PCs). Activation of P2Y purinoceptors by two selective agonists, ADP and 2-methylthio-ADP (2MeSADP), elicited two distinct forms of synaptic plasticity of GABAergic transmission in the cerebellar cortex. First, the two agonists induced long-lasting enhancement of stimulation-evoked GABAergic IPSCs as well as GABA(A) receptor currents in PCs. This effect was completely abolished by intracellular infusion of the Ca2+-chelating agent BAPTA. Measurements of intracellular Ca2+ ([Ca2+]i) dynamics showed that puff application of 2MeSADP produced an increase in [Ca2+]i of PCs and that this increase persisted in an external Ca2+-deficient medium. These results suggest that P2Y activation postsynaptically elicits long-term enhancement of GABA(A) receptor sensitivity of PCs through a Gq-mediated increase in [Ca2+]i. The other action of P2YR agonists on cerebellar GABAergic synapses was that they produced a short-term increase in the frequency and the amplitude of spontaneous GABAA receptor-mediated IPSCs in PCs in a manner sensitive to a P2Y1R antagonist, N6-methyl 2'-deoxyadenosine 3',5'-bisphosphate. This action appeared to be attributable to an excitability increase in presynaptic GABAergic interneurons, because ADP excited all Lugaro cells examined and some of interneurons in the molecular layer. These results suggest that activation of cerebellar P2Y purinoceptors leads to modulation of GABAergic transmission in different spatial and temporal domains, namely short-term and long-term plasticity through presynaptic and postsynaptic mechanisms at interneuron-->PC inhibitory synapses in the rat cerebellar cortex.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2003

Increased sensitivity to halothane but decreased sensitivity to propofol in mice lacking the N-type Ca2+ channel.

Volatile anesthetics are known to depress excitatory synaptic transmission. Inhibition of voltage-dependent Ca2+ channels is speculated to underlie this mechanism, which remains to be clarified in vivo. We examined the sensitivity to halothane in mice lacking the N-type Ca2+ channel, a major contributor of presynaptic neurotransmitter release. Sensitivity to halothane was significantly increased in the knockout mice compared with the wild-type littermates. Halothane also depressed field excitatory postsynaptic potentials recorded from the Schaffer collateral-CA1 hippocampal synapses more greatly in the knockout mice. We further examined sleep time induced by injection of propofol, an intravenous anesthetic that mainly affects inhibitory synaptic transmission. In contrast, sensitivity to propofol was significantly decreased in the knockout mice. We suggest that inhibition of the N-type Ca2+ channel underlies mechanisms of halothane anesthesia but counteracts propofol anesthesia.

Anesthetics, Inhalation↗
PubMed2003

Anesthetic sensitivities to propofol and halothane in mice lacking the R-type (Cav2.3) Ca2+ channel.

UNLABELLED: Because inhibition of voltage-dependent Ca(2+) channels can be a mechanism underlying general anesthesia, we examined sensitivities to propofol and halothane in mice lacking the R-type (Ca(v)2.3) channel widely expressed in neurons. Sleep time after propofol injection (26 mg/kg IV) and halothane MAC(RR) and MAC (50% effective concentrations for the loss of the righting reflex and for the tail pinch/withdrawal response, respectively) were determined. Significantly shorter propofol-induced sleep time (291.6 +/- 16.8 s versus 344.4 +/- 12.1 s) and larger halothane MAC(RR) (1.11% +/- 0.04% versus 0.98% +/- 0.03%) were observed in Ca(v)2.3 channel knockouts (Ca(v)2.3(-/-)) than in wild-type (Ca(v)2.3(+/+)) litter mates. To investigate the basis of the decreased anesthetic sensitivities in vivo, field excitatory postsynaptic potentials and population spikes (PSs) were recorded from Schaffer collateral CA1 synapses in hippocampal slices. Propofol (10-30 micro M) inhibited PSs by potentiating gamma-aminobutyric acid-ergic inhibition, and this potentiation was markedly smaller at 30 micro M in Ca(v)2.3(-/-) mice, possibly accounting for the decreased propofol sensitivity in vivo. Halothane (1.4%-2.2%) inhibited field excitatory postsynaptic potentials similarly in both genotypes, whereas 1%-2% halothane depressed PSs more in Ca(v)2.3(-/-) mice, suggesting the postsynaptic role of the R-type channel in the propagation of excitation and other mechanisms underlying the increased halothane MAC(RR) in Ca(v)2.3(-/-) mice. IMPLICATIONS: Because inhibition of neuronal Ca(2+) currents can be a mechanism underlying general anesthesia, we examined anesthetic sensitivities in mice lacking the R-type (Ca(v)2.3) Ca(2+) channels both in vivo and in hippocampal slices. Decreased sensitivities in mutant mice imply a possibility that agents blocking this channel may increase the requirements of anesthetics/hypnotics.

Anesthetics, Inhalation↗
PubMed2002

Ca(v)2.3 (alpha1E) Ca2+ channel participates in the control of sperm function.

To know the function of the Ca2+ channel containing alpha(1)2.3 (alpha1E) subunit (Ca(v)2.3 channel) in spermatozoa, we analyzed Ca2+ transients and sperm motility using a mouse strain lacking Ca(v)2.3 channel. The averaged rising rates of Ca2+ transients induced by alpha-D-mannose-bovine serum albumin in the head region of Ca(v)2.3-/- sperm were significantly lower than those of Ca(v)2.3+/+ sperm. A computer-assisted sperm motility assay revealed that straight-line velocity and linearity were greater in Ca(v)2.3-/- sperm than those in Ca(v)2.3+/+ sperm. These results suggest that the Ca(v)2.3 channel plays some roles in Ca2+ transients and the control of flagellar movement.

Animals↗
PubMed2002

Role of Ca(v) 2.3 (alpha1E ) Ca2+ channel in ischemic neuronal injury.

We investigated the role of the Ca(v)2.3 (alpha1E) channel in ischemic neuronal injury using Ca(v)2.3 mutant mice. In focal ischemia model with a complete occlusion of the middle cerebral artery in vivo, infarct at 24 h was significantly larger in Ca(v)2.3 mutant mice compared with that in wild-type controls. In vitro Ca2+ imaging studies using hippocampal slices revealed that oxygen-glucose deprivation induced a [Ca2+]i increase in the hippocampal CA1 region more vigorously in Ca(v)2.3 mutant mice than in wild-type controls, and that tetrodotoxin or bicuculline application abolished the difference between the genotypes. These results suggest that the Ca(v)2.3 channel plays a protective role in ischemic neuronal injury by a mechanism in which GABAergic neuronal actions are involved.

Animals↗
PubMed2001

Novel Cav2.1 splice variants isolated from Purkinje cells do not generate P-type Ca2+ current.

The alpha(1)2.1 (alpha(1A)) subunits of P-type and Q-type Ca(2+) channels are encoded by a single gene, Cacna1a. Although these channels differ in the inactivation kinetics and sensitivity to omega-agatoxin IVA, the mechanism underlying these differences remains to be clarified. Alternative splicings of the Cacna1a transcript have been postulated to contribute to the respective properties, however, the splice variants responsible for P-type Ca(2+) channels have not been identified. To explore P-type-specific splice variants, we aimed at cloning alpha(1)2.1 from isolated mouse Purkinje cells using single-cell reverse transcription-PCR, because in Purkinje cells P-type currents dominate over the whole currents (>95%) with Q-type currents undetected. As a result, two novel splice variants were cloned. Compared with the previously cloned mouse alpha(1)2.1, two novel variants had additional 48 amino acids at the amino termini, six single amino acid changes, and splicing variations at the exon 46/47 boundary, which produced different carboxyl termini. Furthermore, one variant had one RNA editing site. However, electrophysiological and pharmacological studies indicated that these variants did not generate P-type current in cultured cells. These results suggest that P-type-specific splice variants may exist but that post-translational processing or modification by uncharacterized interacting proteins is also required for generating the P-type current.

Alternative Splicing↗