Mechanism for baclofen inhibition on quantal glutamate release in spinal dorsal horn neurons / 中国药理学通报

Aim To investigate the inhibition mechanisms of baclofen, a specific GABA B receptor agonist, on quantal glutamate release in the rat spinal dorsal horn neurons.Methods Whole-cell voltage-clamp technique was performed on dorsal horn neurons in rat spinal cord slice to record glutamatergic spontaneous miniature excitatory postsynaptic currents (mEPSCs). Baclofen action on quantal glutamate release was assessed by analyzing the change of mEPESC to baclofen perfusion.Results Baclofen(10 ?mol?L -1,50 s) depressed the frequency, but not amplitude distribution of glutamatergic mEPSCs, indicating baclofen presynaptic depression on glutamate release. The depression on frequency of mEPSCs persisted in Ca 2+-free solution, or in the presence of K + conductance blocker, 4-AP. On the other hand, the depression was occluded by forskolin, an activator of adenylate cyclase, but not protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDBu). N-ethylmaleimide (NEM), a sulphydryl alkylating agent, which destroys G protein, abolished baclofen depression.Conclusion Not presynaptic K +, Ca 2+ conductance or PKC, but G protein and/or cAMP pathway are involved in the baclofen depression on glutamate release in rat spinal dorsal horn;this depression might contribute to the analgesic action of baclofen at spinal level.

Increase of L-type calcium current by cGMP-dependent protein kinase regulates in rabbit ventricular myocytes

BACKGROUND: We have previously reported that not only cGMP but also 8-Br-cGMP or 8-pCPT-cGMP, specific and potent stimulators of cGMP-dependent protein kinase (cGMP-PK), increased basal L-type calcium current (ICa) in rabbit ventricular myocytes. Our findings in rabbit ventricular myocytes were entirely different from the earlier findings in different species, suggesting that the activation of cGMP-PK is involved in the facilitation of ICa by cGMP. However, there is no direct evidence that cGMP-PK can stimulate ICa in rabbit ventricular myocytes. In this report, we focused on the direct effect of cGMP-PK an ICa in rabbit ventricular myocytes. METHODS AND RESULTS: We isolated single ventricular myocytes of rabbit hearts by using enzymatic dissociation. Regulation of ICa by cGMP-PK was investigated in rabbit ventricular myocytes using whole-cell voltage clamp method. ICa was elicited by a depolarizing pulse to +10 mV from a holding potential of -40 mV. Extracellular 8-(4-Chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (8-pCPT-cGMP), potent stimulator of cGMP-dependent protein kinase (cGMP-PK), increased basal ICa. cGMP-PK also increased basal ICa. The stimulation of basal ICa by cGMP-PK required both 8-Br-cGMP in low concentration and intracellular ATP to be present. The stimulation of basal ICa by cGMP-PK was blocked by heat inactivation of the cGMP-PK and by bath application of 8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphate, Rp-isomer (Rp-pCPT-cGMP), a phosphodiesterase-resistant cGMP-PK inhibitor. When ICa was increased by internal application of cGMP-PK, IBMX resulted in an additional stimulation of ICa. In the presence of cGMP-PK, already increased ICa was potentiated by bath application of isoprenaline or forskolin or intracellular application of cAMP. CONCLUSIONS: We present evidence that cGMP-PK stimulated basal ICa by a direct phosphorylation of L-type calcium channel or associated regulatory protein in rabbit ventricular myocytes.