SUMMARY1. Bull-frog sympathetic neurones in primary culture were voltage clamped in the whole-cell configuration. The pipette solution contained ATP (5 mM).2. A hyperpolarization-activated sodium-potassium current (H-current: IH) was separated from other membrane currents in a nominally calcium-free solution containing cobalt (2 mM), magnesium (4 mM), barium (2 mm), tetraethylammonium (20 mM), tetrodotoxin (3 /,M), apamin (30 nM) and 4-aminopyridine (1 mm). IH was selectively blocked by caesium (10-300 ,UM).3. The steady-state activation Of IH occurred between -60 and -130 mV. The H-conductance was 4-1-6-6 nS at the half-activation voltage of -90 mV. With the concentrations of potassium and sodium ions in the superfusate at 20 and 70 mm, respectively, the reversal potential of IH was about -20 mV. IH was activated with a time constant of 2-8 s at -90 mV and 22 'C. The Q10 between 16 and 26 'C was 4-3. 4. A non-hydrolysable ATP analogue in the pipette solution did not support IH activation. Intracellular 'loading' of GTP-y-S (30-500,M) led to a progressive activation of IH-5. Forskolin (10 ,UM) increased the maximum conductance ofIH by 70 %. This was associated with a depolarizing shift in the half-activation voltage (5-10 mV) and in the voltage dependence of the activation/deactivation time constant ofIH.6. Essentially the same results as with forskolin were obtained by intracellular 'loading' with cyclic AMP (3-10 /LM) or bath application of 8-bromo cyclic AMP (0-1-1 mM), dibutyryl cyclic AMP (1 mM) and 3-isobutyl-1-methylxanthine

SUMMARY1. Voltage-clamp recordings were made from neurones in rabbit vesical pelvic ganglia by using single microelectrodes filled with 2 M-caesium chloride. Neurones were superfused with Krebs solution containing 300 nM-tetrodotoxin and 50 mMtetraethylammonium.2. Depolarizing voltage jumps activated inward currents followed by slowly decaying inward tail currents at -30 to +30 mV, which were accompanied by a large increase in membrane conductance. Both the inward current and tail current were blocked by cobalt (2 mM) or in a Krebs solution containing zero calcium and 12 mM-magnesium.3. Substitution of barium for calcium enhanced the inward current, while it strongly reduced the tail current. Strontium substitution still exhibited both the inward current and the tail current.4. Lowering external chloride activity increased the tail current amplitudes without affecting an initial calcium current. The reversal potentials of the tail current, measured using a twin-pulse protocol, were -18+5 mV (mean+s.E.M., n = 8) and +5+3 mV (n = 5) in Krebs solution and low-chloride (62 mM) solution, respectively, suggesting a calcium-dependent chloride current.

No abstract

Effects of 5-hydroxytryptamine (5-HT) on EPSPs and EPSCs in the rat dorsolateral septal nucleus (DLSN) were examined in the presence of GABA(A) and GABA(B) receptor antagonists. Bath application of 5-HT (10 microm) for 5-10 min increased the amplitude of the EPSP and EPSC. (+/-)-8-hydroxy-2-(di-N-propylamino)tetralin hydrobromide (10 microm), an agonist for 5-HT1A and 5-HT7 receptors, did not facilitate the EPSP. alpha-Methyl-5-HT (10 microm), a 5-HT2 receptor agonist, increased the amplitude of the EPSC. Alpha-methyl-5-(2-thienylmethoxy)-1H-indole-3-ethanamine (10 microm) and 6-chloro-2-(1-piperazinyl)pyrazine (10 microm), selective 5-HT2B and 5-HT2C receptor agonists, respectively, had no effect on the EPSP. The 5-HT-induced facilitation of the EPSP was blocked by ketanserin (10 microm), a 5-HT2A/2C receptor antagonist. However, N-desmethylclozapine (10 microm), a selective 5-HT2C receptor antagonist, did not block the facilitation of the EPSP induced by alpha-methyl-5-HT. The inward current evoked by exogenous glutamate was unaffected by 5-HT. 5-HT (10 microm) and alpha-methyl-5-HT (10 microm) increased the frequency of miniature EPSPs (mEPSPs) without changing the mEPSP amplitude. The ratio of the paired pulse facilitation was significantly decreased by 5-HT and alpha-methyl-5-HT. The 5-HT-induced facilitation of the EPSP was blocked by calphostin C (100 nm), a specific protein kinase C (PKC) inhibitor, but not by N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (10 microm), a protein kinase A inhibitor. Phorbol 12,13-dibutyrate (3 microm) mimicked the facilitatory effects of 5-HT. These results suggest that 5-HT enhances the EPSP by increasing the release of glutamate via presynaptic 5-HT2A receptors that link with PKC in rat DLSN neurons.

1 The sensitivity of the nicotinic acetylcholine (ACh)-receptor, measured as the amplitude of ACh-current induced by iontophoretic application of ACh to the frog skeletal muscle endplate, was increased by the action of adenosine triphosphate (ATP). 2 This potentiation was not due to the effect of ATP on ACh-esterase, since the increase of the sensitivity could also be demonstrated by use of carbachol (CCh). 3 Kinetic analysis of the effect of ATP on the dose-response curve of CCh-current suggests that ATP increases the ACh-sensitivity by acting on the allosteric site of receptor-ionic channel complex without changing the affinity of ACh for its recognition site. 4 The equilibrium potential and the life-time of the endplate current (e.p.c.) are not altered by the presence of ATP. 5 These results suggest that ATP increases the ACh-sensitivity by increasing either the conductance of unit channels or the total number of available channels.