This article is looking at how two intracellular solutions of Kmeth or Kgluc can affect membrane properties. It shows the immediate and gradual effects of these solutions on: Measurement of AHP Measurement of basic membrane properties, such as resistance Induction of AHP plasticity in CA1 pyramidal neurons.
Male Wistar rats- postnatal day 14-28 Whole cell and perforated-patch recordings Electrodes filled with either 115mM Kmeth or 115mM Kgluc Resistance= 2-4 mega ohms Comparisons with perforated-patch recordings were made to determine which internal solution best preserved the AHP.
First they used a conventional high- frequency train of action potentials (50 action potentials at 50Hz). Second, they used theta-burst firing (10 bursts of 5 action potentials (1nA at 100Hzwith an interburst frequency at 5Hz). AHPs elicited by alternating between theta-burst firing and 50Hz firing.
Apamin-selective small- conductance calcium- activated potassium channel blocker (types 2 and 3) › When applied it reduced the average membrane potential of the AHP › The portion of the AHP sensitive to apamin is the mAHP › Apamin has been shown to selectively block the AHP current, therefore size of this current does not depend on the internal anions.
Apamin partially blocked mAHP, they believed the remainder of the mAHP is driven by the activation of slow AHP current. › Applied noradrenaline (NA), a greater fraction of the mAHP was inhibited by NA when in KMeth as compared to KGluc. › The slow AHP current contributes to the mAHP; this current is larger in recordings using Kmeth than in those using KGluc
The AHP was larger in KMeth than in KGluc; they were interested in determining whether Kmeth artificially enhances the AHP or if Kgluc artificially reduces it. Found that the average negative membrane potential during the mAHP and sAHP was significantly greater in Kmeth than in Kgluc. It seems as though under certain circumstances Kmeth may artificially enhance the AHP.
Action potential and fADP smaller in Kmeth than Kgluc After 5-10 min of recording neuron resistance, current threshold, and threshold were significantly different in Kmeth and Kgluc
fADP in whole cell recording was preserved in Kmeth It was reduced in perforated-patch recordings using Kmeth higher action potential and reduction in spike height
o Mean amplitude of mAHP and sAHP in Kmeth were stable over the duration of the experiment (low activity) o AHPs in low activity were stable in Kgluc fADP in Kmeth reduced at late time point. In Kgluc it was stable (low activity) fADP reduced in Kmeth (minimal activity). Conclusion: firing mode and excitability of CA1 pyramidal neurons is altered when using Kmeth.
Kmeth caused an increase in neuron resistance, independent of activity level. mAHP and early sAHP were reduced in conditions of high activity, but not low activity The plasticity of the AHP observed reflects a change in the intrinsic properties of the neuron.
Kgluc-stable measures of neuron resistance and current threshold Kmeth-neuron resistance increased and current threshold decreased. Induction of activity-dependent plasticity of AHP only observed in Kgluc; AHP was masked using Kmeth Kgluc provides a more stable long-term recording environment than Kmeth. Found that AHP was stable at a low rate regardless of the main anion.
Reduction of AHP is activity dependent › Reduction in AHP results in increases in neuronal excitability. › Facilitates LTP (long term potentiation Enhancement of AHP may facilitate LTD (long term depression).