Bullfrog Sympathetic Ganglion Cells Research Articles

Effects of Na + gradient on the intracellular Ca 2+ oscillation in the sympathetic ganglion cell: NaCa exchange in the neurone cell soma?

The effects of the removal of extracellular Na + and the increase in the intracellular Na + on the slow rhythmic membrane hyperpolarizations (rmhs) were studied in bullfrog sympathetic ganglion cells. The interval of rmhs, reflecting a relative change in the basal intracellular Ca 2+, was lengthened by either treatment, disfavouring the possible involvement of the NaCa exchange mechanism in the Ca 2+-buffering in the ganglion cell soma.

(+)-Tubocurarine blocks the Ca 2+-dependent K +-channel of the bullfrog sympathetic ganglion cell

(+)-Tubocurarine ((+)-Tc:10–100 μM) reduced the duration of the afterhyperpolarization, which was induced by the activation of Ca 2+-dependent K +-conductance (G K,Ca) following an action potential in the bullfrog sympathetic ganglion cell, but did not affect the maximum rates of rise and fall of Na +- and Ca 2+-dependent action potentials. The amplitudes of slow rhythmic membrane hyperpolarizations produced by rhythmic rises in the G K,Ca were also decreased by (+)-Tc without a change in their intervals. Thus, (+)-Tc appears to block the Ca 2+-dependent K +-channel of the bullfrog sympathetic ganglion cell.

Restoration of the nicotinic receptor-channel activity from the blockade by atropine in bullfrog sympathetic ganglia

Atropine (3 μM) reduced both the nicotinic and muscarinic acetylcholine (ACh) potentials of the bullfrog sympathetic ganglion cell. However, the former was completely restored within 1 h during a sustained exposure to atropine, while the latter remained blocked. Similar restorations were observed for the depressant effects on both the amplitude and decay phase of a nerve-induced postsynaptic current. The results suggest that the sustained or repetitive binding of atropine to this site results in a new conformational state capable of passing ions almost normally, but resistant to the blockade by atropine.

Modulation of action potential during the late slow excitatory postsynaptic potential in bullfrog sympathetic ganglia

The spike peak and after-hyperpolarization of the action potential of bullfrog sympathetic ganglion cells were depressed during the late slow excitatory postsynaptic potential (EPSP). These changes in the action potential were mimicked by luteinizing hormone-releasing hormone (LH-RH), a neurotransmitter candidate for the late show EPSP. LH-RH (5 μM) suppressed the voltage-dependent K + currents, both the delayed rectifier K + current (I K1) and the M current (I K2). It is suggested that the depression of the after-hyperpolarization of the action potential during the late slow EPSP may be due to suppression of I K1 and I K2.

Substance P inhibits the action potentials in bullfrog sympathetic ganglion cells

Substance P depressed the spike and after-hyperpolarization of action potentials of bullfrog sympathetic ganglion cells. It also depressed the after-hyperpolarization and prolonged the falling phase in Ca 2+ spikes. The voltage-dependent K + currents, both the delayed rectifier K + current (I K1) and the M current (I K2),were suppressed by substance P, suggesting that the depression of the after-hyperpolarization may be due to suppression of these K + currents.

Substance P modulates the sensitivity of the nicotinic receptor in amphibian cholinergic transmission.

The effect of substance P on the sensitivity of nicotinic acetylcholine (ACh) receptors of bullfrog sympathetic ganglion cells and frog skeletal muscle endplate was examined electrophysiologically. The amplitude of ACh-induced postsynaptic potential (ACh potential) and current (ACh current) were reversibly and dose-dependently reduced by substance P at low concentrations (0.42-42 microM). The mean amplitude of the miniature endplate potential (m.e.p.p.) was also reduced by substance P (4.2 microM). Substance P (4.2 microM) shifted the S-shaped dose-response curve of the ACh current downward. A Lineweaver-Burk plot constructed from the dose-response curve revealed that substance P depressed the maximum response (Vmax) without changing the apparent affinity (Km) of ACh for the receptor. Substance P (0.42-42 microM) did not alter the reversal potential of the ACh current of the endplate. The half-decay time of endplate current (e.p.c.) and its voltage-dependency were not altered by substance P in these concentrations. The depression of the ACh current by substance P may not be due to a blockade of the opened channel which has been activated by the preceding combination of ACh with the receptor. These results suggest that substance P suppresses the sensitivity of nicotinic ACh-receptors of the sympathetic ganglion cell and skeletal muscle endplate, acting on a certain allosteric site but not the recognition site of ACh in the receptor-ionic channel complex.

Does intracellular release of Ca 2+ participate in the afterhyperpolarization of a sympathetic neurone?

The afterhyperpolarization (AHP) of an action potential in the bullfrog sympathetic ganglion cell was highly sensitive to anions (a factor affecting Ca 2+ release 16) filled in a recording electrode; it was slower for citrate ion than for Cl −. The AHP recorded with a ‘KCl-electrode’ was suppressed drastically by D-600 (Ca 2+-antagonist 6) and prolonged significantly by caffeine (promoting Ca 2+ release 4,9), while the AHP recorded with a ‘K 3-citrate-electrode’ was affected only slightly by these agents. Thus, these results suggest that Ca 2+ entry during an action potential is the main origin of Ca 2+ for the AHP recorded with a ‘KCl-electrode’, and favour the idea that the intracellular release of Ca 2+ by an action potential as well as the Ca 2+ influx participates in the mechanism of the AHP recorded with a ‘K 3-citrate-electrode’.

Kinetic analysis of atropine-induced alterations in bullfrog ganglionic fast synaptic currents.

The concentration- and voltage-dependent effects of atropine on the fast excitatory post-synaptic current (e.p.s.c.) of bullfrog sympathetic ganglion cells have been analysed and fitted to a kinetic scheme of open-channel blockade. Atropine (1-75 microM) reduced the peak e.p.s.c. amplitude without altering the quantal content or the reversal potential. The e.p.s.c. decay was complex in the presence of atropine, being well fitted by two exponential components. With increasing concentrations of atropine the time constant of the fast component, tau 2, decreased and the time constant of the slow component, tau 1, increased. Over the voltage range -30 to -100 mV tau 2 exhibited little or no voltage dependence and tau 1 increased with hyperpolarization. The amount of charge moved during the e.p.s.c. was reduced as a function of atropine concentration. Driving functions, which represented the rate of channel opening, were derived from e.p.s.c.s both from control and atropine-treated cells. The characteristics of the driving functions did not vary with membrane voltage, but the driving functions were shorter in duration from atropine-treated than control cells. The area under the driving function decreased as a function of atropine concentration. The decay time constants and the amplitude ratio of the exponential components were used to calculate the closing, blocking, and unblocking rate constants, alpha, G, and F. alpha and F remained constant with increasing atropine concentration, but G declined significantly. The voltage dependence of the equilibrium constant, G/F, implied that the transient blocking site for atropine is halfway through the ionic channel. The sequential model does not predict the concentration-dependent decrease in the blocking rate, G, or in the charge moved during an e.p.s.c. We conclude that atropine has an action more complex than simple channel blockade in sympathetic ganglion cells.

Modulatory actions of ATP on membrane potentials of bullfrog sympathetic ganglion cells

Adenosine triphosphate (ATP) depolarized the membrane of bullfrog sympathetic ganglion cells by decreasing resting K + conductance. ATP also depressed the maximum amplitude of after-hyperpolarization of action potentials. Voltage-clamp study revealed that ATP markedly suppressed the TEA-insensitive K + current which appeared to correspond to the M-current 7, while it affected less significantly on the delayed rectifier K + current. It was suggested that ATP depolarized resting membrane by suppressing resting K + conductances, including the M-current, and also depressed the after-hyperpolarization of action potentials by suppressing both the M-current and delayed rectifier K + current.

Voltage-clamp analysis of peptidergic slow depolarizations in bullfrog sympathetic ganglion cells.

1. The membrane currents during the late slow excitatory post-synaptic potential (late slow e.p.s.c.s) and luteinizing hormone-releasing hormone (LHRH)-induced depolarization of nicotinized and atropinized bullfrog lumbar sympathetic ganglion cells were studied with voltage-clamp methods. 2. Two types of late slow e.p.s.c. were observed. The Type I response was associated with a decreased conductance and was depressed by membrane hyperpolarization. The Type II response was accompanied by an increased conductance and was augmented by membrane hyperpolarization. 3. LHRH also induced two types of responses. The nature of the LHRH-induced current and the late slow e.p.s.c. in each neurone was similar, if not identical. 4. The Type I response appeared to be produced primarily by a suppression of the M current (Brown & Adams, 1980) and partially by a depression of the resting K+ conductance. The Type II response is probably due to an increased conductance to Na+ or Na+ and some other cations.

Identification of g K systems activated by [Ca 2+

Rhythmic caffeine hyperpolarizations generated in bullfrog sympathetic ganglion cells are assumed to be caused by periodic increase in g K due to rise in [Ca 2+] i 7−9,13. Caffeine-induced outward currents seem to be composed of two different components, which show different pharmacological natures and also different dependencies on membrane potential changes. These two components may be generated by activations of two voltage-dependent K + currents, namely I K1 (the delayed rectifier K + current and I K2 (I M) of ganglion cells. These results suggested that at least two different g K systems were activated by [Ca 2+] i in sympathetic ganglion cells.

Catecholamine modulates nicotinic ACh-receptor sensitivity

The sensitivity of nicotinic acetylcholine (ACh) receptors is modulated by the action of catecholamines in both bullfrog sympathetic ganglion cells and frog skeletal muscle end-plates. According to analyses of the effects of catecholamine on the dose-response curve of the ACh-induced end-plate current and also on the end-plate current (EPC), catecholamines appear to depress the ACh-receptor sensitivity by decreasing the conductance of unit ionic channels of the nicotinic ACh-receptor complex.

Modulation of voltage-dependent currents by muscarinic receptor in sympathetic neurones of bullfrog

The muscarinic actions of acetylcholine (ACh) on the action potentials of bullfrog sympathetic ganglion cells were studied with voltage-clamp experiments. The slow inward current (I si) carried by Ca 2+ was markedly depressed by ACh. ACh also markedly depressed the time-dependent outward current following I si. The outward current was composed of two components, a TEA-sensitive rectifier K + current (I K1) and a TEA-insensitive slow rectifier K + current (I K2). Both of these components were depressed by ACh.

Modulation of the slow inward Ca2+ current by adrenaline in bullfrog sympathetic ganglion cells.

The slow inward current, which is carried almost exclusively by Ca2+, was disclosed by voltage-clamp study on bullfrog sympathetic ganglion cells in Ringer solution. This current was confirmed to be markedly depressed by the action of adrenaline, suggesting that adrenaline modulates the Ca2+ influx of ganglion cells under physiological conditions.

Simulation of intracellular Ca 2+ oscillation in a sympathetic neurone

Three different theoretical models were considered for the mechanism of the oscillation of the intracellular free Ca 2+ ([Ca 2+] i) linked to the K + conductance of the plasma membrane ( G K) observed in bullfrog sympathetic ganglion cells. The models assumed a Ca 2+-induced Ca 2+ release mechanism, an active Ca 2+ uptake mechanism at a Ca 2+ reservoir site in the ganglion cell, and a Michaelis—Menten type relationship between [Ca 2+] i and G K. Including both active and passive Ca 2+ transport mechanisms at the plasma membrane, either a one-compartment model or a two-compartment model for the intracellular Ca 2+ store reconstructed successfully the [Ca 2+] i oscillation and rhythmic membrane hyperpolarizations observed in the ganglion cell, and simulated most of their characteristics. On the other hand, a two-compartment model disregarding of Ca 2+ transport at the plasma membrane failed to reproduce the oscillations of [Ca 2+] i and membrane potential.

Voltage-clamp studies of a slow inward current in bullfrog sympathetic ganglion cells

Voltage-dependent inward membrane currents of bullfrog sympathetic ganglion cells were analyzed with the voltage clamp method. Two distinct inward currents, a tetrodotoxin (TTX)-sensitive fast inward current (I Na) and a TTX-insensitive slow inward current (I si), were recorded in Ringer solution. The I si was markedly depressed by removal of external Ca 2+ and by the addition of Mn 2+, Co 2+ or D-600. This suggests that the I si is, almost exclusively, due to Ca 2+. These results indicate that under physiological conditions a Ca 2+ influx is induced during initiation of action potentials in these ganglion cells.

5-Hydroxytryptamine controls ACh-receptor sensitivity of bullfrog sympathetic ganglion cells

Experimental evidences showing that 5-hydroxytryptamine (5-HT) is directly interacting with nicotinic acetylcholine (ACh) receptors and thereby depresses the sensitivity of these receptors to ACh, are presented by making use of bullfrog sympathetic ganglion cells and frog skeletal muscle end-plates. It was suggested that 5-HT might decrease the affinity of ACh to nicotinic receptor sites, since the mode of 5-HT action was comparable to that of d-tubocurarine action.

Why do barium ions imitate acetylcholine?

The action of 1–4 mM barium on bullfrog sympathetic ganglion cells was studied using voltage clamp. Barium imitated the action of muscarine, causing depolarization, increased input resistance, tendency to repetitive firing, and a specific inhibition of a slow small outward current termed the M current. Barium did not produce significant short-term inhibition of three other outward currents; the delayed rectifier, the calcium-dependent K current, and the A current.

Catecholamine is released from non-synaptic cell-soma membrane: histochemical evidence in bullfrog sympathetic ganglion cells

Catecholamine is released from non-synaptic cell-soma membrane: histochemical evidence in bullfrog sympathetic ganglion cells

Desensitization of the muscarinic receptor controlling action potentials of sympathetic ganglion cells in bullfrogs

The desensitization of the muscarinic receptor, of which activation is known to depress the ionic K + and Ca 2+ currents generated during action potentials of bullfrog sympathetic ganglion cells, was studied. The depression of these voltage-dependent K + and Ca 2+ currents by muscarinic action of acetylcholine (ACh) was gradually restored to a certain extent when an application of ACh was sustained. After removal of ACh, the sensitivity of the muscarinic receptor was still depressed for an extended period, while resting and action potentials were apparently observed to be of normal level and size, respectively. These results indicate that desensitization of muscarinic receptors developed during a sustained application of ACh. It was suggested that the muscarinic receptor controlling these voltage-dependent currents of ganglion cells may be part of receptor-ionic channel complex (RICC) the nature of which was comparable to that of the RICC of the nicotinic receptor of the end-plate.