Related Experiment Video
Updated: Aug 19, 2026

GABA-activated Single-channel and Tonic Currents in Rat Brain Slices
Published on: July 17, 2011
Ca2+ currents in cerebellar granule neurones: role of internal Mg2+ in altering characteristics and antagonist
H A Pearson1, K G Sutton, R H Scott
1Department of Pharmacology, Royal Free Hospital School of Medicine, London, U.K.
Abstract:
Using the whole-cell patch-clamp technique, Ca2+ channel currents were measured in cultured rat cerebellar granule neurones in the presence of 10 mM Ba2+. Two different solutions were used to fill patch pipettes, one containing mainly tetraethylammonium acetate (TEA-Ac solution), and the other mainly caesium and HEPES (Cs-HEPES solution). Under these two different intracellular conditions markedly different Ca2+ channel currents were recorded. When TEA-Ac solution was used intracellularly, small, Cd(2+)-sensitive inward currents (approx. -55 pA) that were inhibited by the dihydropyridine antagonist (-)-202-791 and the GABAB agonist (-)-baclofen were observed. These currents were insensitive to the Ca2+ channel clocking toxins omega-conotoxin GVIA (omega-CgTX) and omega-agatoxin IVA and were enhanced by the dihydropyridine agonist (+)-202-791. In contrast, when the Cs-HEPES solution was used, currents were 2-3 times larger (approx. -130 pA), inhibited by (-)-202-791, omega-CgTX and omega-agatoxin IVA but were unaffected by (-)-baclofen. Furthermore, both (+)-202-791 and Bay K8644 in the presence of Cs-HEPES solution produced only a transient enhancement that was followed by an inhibition. Analysis of steady-state inactivation revealed two components of current in both cases, with similar voltage dependencies. The factor(s) giving rise to these differences were investigated in terms of current amplitude and responses to (-)-baclofen and omega-CgTX and were found to be mainly due to the concentrations of Mg2+ and ATP added to the patch pipette solutions. Furthermore, free internal Mg2+ concentrations of greater than 0.2 mM selectively inhibited omega-CgTX-sensitive Ca2+ channels. Preliminary evidence indicates that the same may be true of omega-Aga IVA-sensitive P-type current. These data suggest that the N-type Ca2+ channels in these cells are preferentially inhibited by intracellular Mg2+ and this may provide an explanation for discrepancies between the results of different groups investigating Ca2+ channel currents in similar cell types.
Related Concept Videos
The Role of Ion Channels in Neuronal Computation
Sometimes a single EPSP is strong enough to induce an action potential in the postsynaptic neuron. However, multiple presynaptic inputs must often create EPSPs around the same time for the postsynaptic neuron to be sufficiently depolarized to fire an action potential.
G-Protein Gated Ion Channels
Sensory organs,...
Feedback Regulation of Calcium Concentration
Various transmembrane receptors, such as G protein-coupled receptors (GPCRs), elicit a response to extracellular signals by increasing cytosolic calcium. Activated GPCRs...
Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
Ligand-Gated Ion Channel Receptor: Gating Mechanism
Cholinergic Receptors: Muscarinic
The subtypes M1, M3, and M5 couple with the Gq subunit and activate the phospholipase C (PLC) activity, mobilizing intracellular Ca2+. Activation...

