WITHDRAWN: Inhibitory effects of D-Serine on hippocampal synapse transmission.

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Similarities of SP-, NKA- and NKB-induced currents in rat dorsal root ganglion neurons.

Tachykinin (TK; including substance P (SP), neurokinin A (NKA) and neurokinin B (NKB))-induced currents (I(TK)s) were studied in freshly isolated rat dorsal root ganglion (DRG) neurons using whole-cell patch clamp recording and repatch techniques. All the three I(TK)s manifested features of fast activating kinetics, such as short latency and fast tau(on) and tau(off), and very slow desensitization. The concentration-response relationships for TKs show: (1). compared with the concentration-response curve for NKA, the curve for NKB shifted upwards, while that for SP shifted downwards; (2). the EC(50) values for NKB-, NKA- and SP-activated currents were very close to each other. The I-V curves for the three TKs were basically linear and arrayed in the order of NKB>NKA>SP; the reversal potentials for the three I(TK)s were all around +15 mV. Replacement of NaCl in the external solution by equimolar N-methyl-D-glucamine (NMDG) attenuated both NKA- and NKB-activated currents markedly, as it was the case with SP-activated current caused by the opening of Na(+) preferring non-selective cation channels observed in our previous work. All the three TKs proved to inhibit coexistent GABA(A) receptor-mediated current (I(GABA)); this effect was removed by intracellular dialysis of GDP-beta-S or H-7. However, these drugs did not block the SP-, NKA- and NKB-activated currents at all, which indicated that I(TK)s were G-protein independent. In short, the responses of rat DRG neurons to SP, NKA and NKB were similar in essence, although the amplitudes of currents induced by the same concentration of the three TKs were different. Taking the results of this study and our previous studies together, we hypothesized that SP, NKA and NKB may induce inward currents through undiscovered channels that are associated with tachykinins receptors (NK1R, NK2R, NK3R, which have already been cloned), but independent of G-protein coupling and remains to be further investigated.

Three kinds of current in response to substance P in bullfrog DRG neurons.

In response to SP applied externally, neurons freshly isolated from bullfrog dorsal root ganglion (DRG) showed three kinds of current (I(SP)), i.e. slow, fast and moderately activating I(SP)s. All the three kinds of I(SP) were inward currents, and were completely blocked by either peptide antagonist of SP receptor spantide or non-peptide antagonist of SP receptor WIN51708. The slow activating I(SP) showed slow kinetic features. Replacement of NaCl in external solution by NMDG had no effect on this kind of I(SP), while Ba(2+) abolished it almost completely, thus the ionic mechanism underlying slow activating I(SP) was deduced to be the closure of K(+) channels. The fast activating I(SP) in bullfrog DRG neurons, just as in rat DRG neurons, was proved to be caused by the opening of Na(+) preferring non-selective cation channel, for it was abolished almost completely by replacement of NaCl in external solution with equimolar NMDG. The moderately activating I(SP) was similar to the fast activating I(SP) in current configuration, however, its kinetic characteristics lay between those of fast and slow activating I(SP)s. Either NMDG or Ba(2+) suppressed this kind of I(SP) partially. Therefore the moderately activating I(SP) might be mediated by non-selective cation channel. We used repatch technique to explore the intracellular mechanism underlying the three kinds of I(SP) and found that the three kinds of I(SP) were caused by the activity of either G-protein coupled channel (slow activating I(SP)) or directly opened channel (fast activating I(SP)) or both (moderately activating I(SP) ).

Modulatory effect of substance P on GABA-activated currents from rat dorsal root ganglion.

AIM: To explore the modulatory effect of substance P (SP) on GABA-activated current of dorsal root ganglion (DRG) neurons in rat. METHODS: The whole-cell patch-clamp technique was used to record SP- and GABA-activated currents in neurons freshly dissociated from rat DRG neurons. Drugs were applied by rapid solution exchange. RESULTS: Application of SP (28/41, 68.5 %) and GABA (36/41, 88.2 %) could induce concentration-dependent inward current in some cells. SP-(10 micromol/L) and GABA (100 micromol/L)-activated inward currents were (244+/-83) pA (n=9) and (1.8+/-0.5) nA (n=13), respectively. The majority of GABA-activated current had obvious three processes, the peak value (I(p)), the steady state (I(ss)) and the desensitization (I(d)). The desensitization of GABA-activated current was a biphasic process, including fast and slow desensitization. However, pre-application of SP (0.001-1 micromol/L) could inhibit the GABA-activated inward current which was identified to be GABAA receptor-mediated current. The inhibitory effects were concentration-dependent. The inhibitory effect of SP on the peak value of GABA-activated current was more than the steady state of GABA-activated current. The inhibition of GABA-activated current by SP (0.1 micromol/L) was related to the time after application of SP, the inhibition of GABA-activated currents by SP reached the peak at about 4 min (49.8 %+/-7.2 %, n=7, P<0.01) and took about 12 min to get a full recovery. The inhibition of GABA-activated currents by SP was almost completely removed after blockade of PKC by H-7 with the re-patch clamp. CONCLUSION: Pre-application of SP exerts a more strong inhibitory effect on the peak value of GABA-activated current than the steady state of GABA-activated current.