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The action of high K+ and aglycaemia on the electrical properties and synaptic transmission in rat intracardiac ganglion neurones in vitro.

Dyavanapalli J, Rimmer K, Harper AA - Exp. Physiol. (2008)

Bottom Line: High K(+) had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents.However, the combination of aglycaemia and 20 mm K(+) displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K(+) PSS.These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge.

View Article: PubMed Central - PubMed

Affiliation: College of Life Sciences, University of Dundee, UK.

ABSTRACT
We have investigated the action of two elements of acute ischaemia, high potassium and aglycaemia, on the electrophysiological properties and ganglionic transmission of adult rat intracardiac ganglion (ICG) neurones. We used a whole-mount ganglion preparation of the right atrial ganglion plexus and sharp microelectrode recording techniques. Increasing extracellular K(+) from its normal value of 4.7 mm to 10 mm decreased membrane potential and action potential after-hyperpolarization amplitude but otherwise had no effect on postganglionic membrane properties. It did, however, reduce the ability of synaptically evoked action potentials to follow high-frequency (100 Hz) repetitive stimulation. A further increase in K(+) changed both the passive and the active membrane properties of the postganglionic neurone: time constant, membrane resistance and action potential overshoot were all decreased in high K(+) (20 mm). The ICG neurones display a predominantly phasic discharge in response to prolonged depolarizing current pulses. High K(+) had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents. At 20 mm, K(+) practically blocked ganglionic transmission in most neurones at all frequencies tested. Aglycaemia, nominally glucose-free physiological saline solution (PSS), increased the time constant and membrane resistance of ICG neurones but otherwise had no action on their passive or active properties or ganglionic transmission. However, the combination of aglycaemia and 20 mm K(+) displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K(+) PSS. These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge.

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Related in: MedlinePlus

‘Waterfall’ display of action of high [K+]o on synaptic transmissionThe effects of high K+ on synaptic transmission were investigated by applying trains of 50 stimuli applied at time ‘S’ (10 Hz for A, C and E and 50 Hz for B, D and F) to the preganglionic nerve trunk. The upper panels in A, C and E show voltage with time, records of individual volleys of pulses and the timing of the start and the end of the waterfall. G, the ratio of the number of successful somatic action potentials to the number of stimuli gives an index of the frequency dependence of ganglionic transmission (P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 4.7 versus 20 mm K+; P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 10 versus 20 mm K+, n= 8, RM-ANOVA). *P < 0.05, **P < 0.01 and ***P < 0.005 for 4.7 mm K+versus 20 mm K+; and δP < 0.01 and δδP < 0.005 for 10 mm K+versus 20 mm K+.
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fig06: ‘Waterfall’ display of action of high [K+]o on synaptic transmissionThe effects of high K+ on synaptic transmission were investigated by applying trains of 50 stimuli applied at time ‘S’ (10 Hz for A, C and E and 50 Hz for B, D and F) to the preganglionic nerve trunk. The upper panels in A, C and E show voltage with time, records of individual volleys of pulses and the timing of the start and the end of the waterfall. G, the ratio of the number of successful somatic action potentials to the number of stimuli gives an index of the frequency dependence of ganglionic transmission (P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 4.7 versus 20 mm K+; P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 10 versus 20 mm K+, n= 8, RM-ANOVA). *P < 0.05, **P < 0.01 and ***P < 0.005 for 4.7 mm K+versus 20 mm K+; and δP < 0.01 and δδP < 0.005 for 10 mm K+versus 20 mm K+.

Mentions: Application of 10 mm K+ PSS had little effect on ganglionic transmission evoked by either single or multiple trains of stimuli (see Figs 4 and 6).


The action of high K+ and aglycaemia on the electrical properties and synaptic transmission in rat intracardiac ganglion neurones in vitro.

Dyavanapalli J, Rimmer K, Harper AA - Exp. Physiol. (2008)

‘Waterfall’ display of action of high [K+]o on synaptic transmissionThe effects of high K+ on synaptic transmission were investigated by applying trains of 50 stimuli applied at time ‘S’ (10 Hz for A, C and E and 50 Hz for B, D and F) to the preganglionic nerve trunk. The upper panels in A, C and E show voltage with time, records of individual volleys of pulses and the timing of the start and the end of the waterfall. G, the ratio of the number of successful somatic action potentials to the number of stimuli gives an index of the frequency dependence of ganglionic transmission (P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 4.7 versus 20 mm K+; P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 10 versus 20 mm K+, n= 8, RM-ANOVA). *P < 0.05, **P < 0.01 and ***P < 0.005 for 4.7 mm K+versus 20 mm K+; and δP < 0.01 and δδP < 0.005 for 10 mm K+versus 20 mm K+.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2713859&req=5

fig06: ‘Waterfall’ display of action of high [K+]o on synaptic transmissionThe effects of high K+ on synaptic transmission were investigated by applying trains of 50 stimuli applied at time ‘S’ (10 Hz for A, C and E and 50 Hz for B, D and F) to the preganglionic nerve trunk. The upper panels in A, C and E show voltage with time, records of individual volleys of pulses and the timing of the start and the end of the waterfall. G, the ratio of the number of successful somatic action potentials to the number of stimuli gives an index of the frequency dependence of ganglionic transmission (P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 4.7 versus 20 mm K+; P < 0.01 at 0.2–20 Hz, P < 0.001 at 50–100 Hz, 10 versus 20 mm K+, n= 8, RM-ANOVA). *P < 0.05, **P < 0.01 and ***P < 0.005 for 4.7 mm K+versus 20 mm K+; and δP < 0.01 and δδP < 0.005 for 10 mm K+versus 20 mm K+.
Mentions: Application of 10 mm K+ PSS had little effect on ganglionic transmission evoked by either single or multiple trains of stimuli (see Figs 4 and 6).

Bottom Line: High K(+) had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents.However, the combination of aglycaemia and 20 mm K(+) displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K(+) PSS.These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge.

View Article: PubMed Central - PubMed

Affiliation: College of Life Sciences, University of Dundee, UK.

ABSTRACT
We have investigated the action of two elements of acute ischaemia, high potassium and aglycaemia, on the electrophysiological properties and ganglionic transmission of adult rat intracardiac ganglion (ICG) neurones. We used a whole-mount ganglion preparation of the right atrial ganglion plexus and sharp microelectrode recording techniques. Increasing extracellular K(+) from its normal value of 4.7 mm to 10 mm decreased membrane potential and action potential after-hyperpolarization amplitude but otherwise had no effect on postganglionic membrane properties. It did, however, reduce the ability of synaptically evoked action potentials to follow high-frequency (100 Hz) repetitive stimulation. A further increase in K(+) changed both the passive and the active membrane properties of the postganglionic neurone: time constant, membrane resistance and action potential overshoot were all decreased in high K(+) (20 mm). The ICG neurones display a predominantly phasic discharge in response to prolonged depolarizing current pulses. High K(+) had no impact on this behaviour but reduced the time-dependent rectification response to hyperpolarizing currents. At 20 mm, K(+) practically blocked ganglionic transmission in most neurones at all frequencies tested. Aglycaemia, nominally glucose-free physiological saline solution (PSS), increased the time constant and membrane resistance of ICG neurones but otherwise had no action on their passive or active properties or ganglionic transmission. However, the combination of aglycaemia and 20 mm K(+) displayed an improvement in passive properties and ganglionic transmission when compared with 20 mm K(+) PSS. These data indicate that the presynaptic terminal is the primary target of high extracellular potassium and that aglycaemia may have protective actions against this challenge.

Show MeSH
Related in: MedlinePlus