Blockade by local anaesthetics of the single Ca²⁺‐activated K⁺ channel in rat hippocampal neurones

Abstract

Effects of local anaesthetics on single Ca2+‐activated K+ channels were investigated using the inside‐out configuration of the patch‐clamp technique in single pyramidal neurones, which were freshly dissociated from rat hippocampus by use of proteolytic enzymes. No significant effect was observed when 2 mm benzocaine was applied on either side of the membrane patch, or when 3 mm lignocaine or QX‐314 was applied to the external surface of the membrane. Lignocaine 1 mm, applied to the internal surface, slightly reduced the amplitude of the single K+ channel current. When applied to the internal surface, QX‐314 reduced the amplitude of the K+ channel current, accompanied by an increase in noise in the open channel current, suggesting a fast flickering block. The blocking effect of QX‐314 on the outward current increased with depolarization, suggesting a binding site for the drug at an electrical distance of about 0.5 across the membrane field. The open time histogram showed one exponential component and the closed time histogram showed at least two components. The mean open time of the outward current was increased when the amplitude was reduced by the drugs. The ionized form of the local anaesthetics had a similar action on the Ca2+‐activated K+ channels to that on Na+ channels, that is, they enter into the channel from the cytoplasmic side to induce open channel block. The blocking kinetics, however, might be so fast that they were beyond the frequency response of our recording apparatus, thus the recorded current amplitude was decreased. In contrast the K+ channel was not accessible via hydrophobic pathways for the neutral form, which is also known to block the sodium channel.

Group I mGluR Activation Causes Voltage-Dependent and -Independent Ca2+Rises in Hippocampal Pyramidal Cells

“…Hyperpolarizing responses elicited by ACPD have been observed previously in CA1 cells and were attributed to the activation of Ca 2ϩ -dependent K ϩ conductances (Jaffe and Brown 1994;Shirasaki et al 1994). QX-314 has been shown to suppress a component of the Ca 2ϩ -dependent K ϩ current (Oda et al 1992). Thus the block of the hyperpolarization by QX-314 ( Fig.…”

The cytosolic inactivation domains of BKi channels in rat chromaffin cells do not behave like simple, open-channel blockers

“…QX-314 results in a marked reduction in the resolvable single-channel current ( Fig. 1 A, inset), which is known to be voltage dependent (Oda et al, 1992). Similarly, 50 ,uM decamethonium ( Fig.…”

Analgesic and sedative concentrations of lignocaine shunt tonic and burst firing in thalamocortical neurones

“…Foehring et al , 1989). Secondly, lignocaine (1 mM) blocks Ca + activated K + channels in hippocampal neurones (Oda et al , 1992), but these channels are of the high conductance type. There is uncertainty about the subcellular distribution of the T‐type Ca 2+ current in VPL neurones and the precise subtype of Ca 2+ channel mediating the LTS.…”