Blocking effect of tricyclopinate on nicotinic receptors in cultured sympathetic neurons.

AIM: To investigate the mechanism of tricyclopinate, an antagonist of nicotinic receptor, on neuronal nicotinic acetylcholine receptors (nAChR). METHODS: A tight seal whole-cell recording patch-clamp technique was performed to record nicotine-evoked currents in the cultured sympathetic neurons from neonatal rat superior cervical ganglia (SCG). RESULTS: Tricyclopinate inhibited the nicotine-induced currents competitively and the inhibition was voltage-independent. The decay of the nicotine-induced current was accelerated significantly in the presence of tricyclopinate. CONCLUSION: Tricyclopinate inhibits neuronal nAChR by interacting with the allosteric sites rather than the open ionic channels or acetylcholine recognition site of the receptor.

Neostigmine competitively inhibited nicotinic acetylcholine receptors in sympathetic neurons.

The present experiment investigates the effect of neostigmine on nicotinic acetylcholine receptors (nAChRs) in the cultured neurons from neonatal rat superior cervical ganglia (SCG). Using whole-cell patch clamp techniques, we found that the amplitudes of the currents induced by 50 microM dimethylphenylpiperazinium (DMPP) were 21.5+/-10.7%, 52.9+/-9.2% and 86.9+/-4.9% depressed at the increased concentrations of neostigmine 100, 200 and 400 microM, respectively. The inhibition of neostigmine decreased gradually with the increased concentration of nicotine from 10 to 160 microM. Lineweaver-Burk's double-reversible plot illustrated that neostigmine blocked neuronal nAChRs in a competitive manner. Hyperpolarization of membrane potential from -40 mV to -100 mV did not significantly influence the blockade of neostigmine. Neostigmine could not accelerate the decay of the DMPP-induced currents, neither evoke any detectable currents in SCG neurons. The results indicate that neostigmine depress neuronal nAChRs in a competitive, concentration-dependent and voltage-independent manner, and can not facilitate desensitization of the receptors. The present data suggest that neostigmine blocks neuronal nAChRs by interacting with the ACh binding sites of the receptors.

Kinetic properties of nicotinic receptors in cultured rat sympathetic neurons from superior cervical ganglia.

AIM: To analyze the kinetic properties of the effect of nicotine on nicotinic acetylcholine receptors (nAChR) in the cultured sympathetic neurons from neonatal rat superior cervical ganglia (SCG). METHODS: The whole-cell recording method of patch-clamp technique was used to record the currents induced by different concentrations of nicotine. The concentration-response of nicotine was fitted with Clark equation. RESULTS: Hill coefficient (1.097) was determined by fitting the nicotine responses of neuronal nAChR with Clark equation. The theoretical values of nicotine effect, calculated with Clark equation with H = 1, were basically identical with the practically recorded currents. CONCLUSIONS: Interaction of nicotine and nAChR in rat SCG fits a single binding site model.

Physostigmine blocked nicotinic acetylcholine receptors in rat sympathetic ganglion neurons.

AIM: To study the blocking mechanism of physostigmine (Phy) on nicotinic acetylcholine receptors (NAChR) in sympathetic neurons. METHODS: The whole-cell patch-clamp technique was used to observe the effects of Phy on NAChR in the cultured sympathetic neurons from neonatal rat superior cervical ganglia (SCG). RESULTS: Phy 5 -20 mumol.L-1 inhibited neuronal NAChR in a concentration-dependent manner and accelerated the desensitization of NAChR. Changing the membrane potential from -50 to -90 mV did not affect the blocking effect of Phy. Phy 200 mumol.L-1 did not induce any noticeable response in SCG neurons. CONCLUSION: Phy blocked NAChR in the sympathetic ganglion neurons by interacting with the allosteric sites out of the binding sites and the open ionic channels of the receptors. Phy did not possess excitative effect on NAChR in SCG neurons.

[45Ca-uptake, mitochondrial protein bound Ca2+ and ultrastructural distribution of Ca2+ in some brain regions of mice during drug-induced analgesia].

After buprenorphine (Bup, 0.8 mg/kg ip) treatment 45Ca-uptake (cpm/mg fresh brain) in vivo by brain slices decreased from 589 +/- 12 and 486 +/- 12 to 522 +/- 14 and 408 +/- 10 and mitochondrial protein bound Tb3+ (Tb3+ relative fluorescent intensity) reduced from 41 +/- 5 and 32 +/- 2 to 30 +/- 3 and 22 +/- 2 in periaqueductal grey and hypothalamus, respectively. A large amount dense precipitate occurred in the myelin sheath and mitochondria in both regions. The 45Ca-uptake evoked by buprenorphine at 16 micrograms/40 microliter in vitro has the similar tendency with that in vivo. Treated by ruthenium red (20 micrograms/mouse ip or icv) before buprenorphine, the above-mentioned effects were all abolished. Similar results were obtained with morphine (Mor, 10 mg/kg ip) and verapamil (Ver, 8 micrograms/mouse icv) instead of buprenorphine and ruthenium red, respectively. These results suggest that Ca2+ transport across neuroplasmic membranes plays a mediator role in drug-induced analgesia.