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Single-channel Currents (single-channel + current)

Distribution by Scientific Domains

Medical Sciences	60%

Selected Abstracts

Characterization of the single-channel properties of NMDA receptors in laminae I and II of the dorsal horn of neonatal rat spinal cord

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2001
G. Mark Green
Abstract The single-channel properties of native NMDA receptors in laminae I and II of the dorsal horn of the neonatal rat spinal cord were studied using outside-out patch-clamp techniques. These receptors were found to have several features that distinguish them from native NMDA receptors elsewhere in the CNS. Single-channel currents activated by NMDA (100 nm) and glycine (10 µm) exhibited five distinct amplitude components with slope-conductance values of 19.9 ± 0.8, 32.9 ± 0.6, 42.2 ± 1.1, 53.0 ± 1.0 and 68.7 ± 1.5 pS. Direct transitions were observed between all conductance levels but transitions between 69-pS openings and 20-, 33- and 42-pS openings were rare. There was no significant difference in the frequency of direct transitions from 42- to 20-pS compared to 20- to 42-pS transitions. The Kb (0 mV) for Mg2+ was 89 µm. The Mg2+ unblocking rate constant was similar to other reported values. However, the Mg2+ blocking rate constant was larger than other reported values, suggesting an unusually high sensitivity to Mg2+. The NR2B subunit-selective antagonist, ifenprodil, had no significant effect on overall channel activity but significantly decreased the mean open time of 53-pS openings. These results suggest neonatal laminae I and II NMDA receptors are not simply composed of NR1 and NR2B subunits or NR1 and NR2D subunits. It is possible that these properties are due to an as yet uninvestigated combination of two NR2 subunits with the NR1 subunit or a combination of NR3A, NR2 and NR1 subunits. [source]

Octanol Modulation of Neuronal Nicotinic Acetylcholine Receptor Single Channels

ALCOHOLISM, Issue 11 2004
Yi Zuo
Background: We have previously shown that alcohols exert a dual action on neuronal nicotinic acetylcholine receptors (AChRs), with short-chain alcohols potentiating and long-chain alcohols inhibiting acetylcholine (ACh)-induced whole-cell currents. At the single-channel level, ethanol increased the channel open probability and prolonged the channel open time and burst duration. In this study, we examined the detailed mechanism of the inhibitory action of the long-chain alcohol n -octanol on the neuronal nicotinic AChR. Methods: Single-channel currents induced by application of 30 nm ACh were recorded with the patch-clamp technique from human embryonic kidney cells stably expressing the human ,4,2 AChR. Results: Several single-channel parameters were markedly changed by octanol. At least two conductance-state currents were induced by low concentrations of ACh, and octanol increased the proportion of the low-conductance-state current relative to the high-conductance-state current without changing the current amplitude. Major analyses of temporal properties of single-channel currents were performed on the high-conductance-state currents. Octanol decreased the burst duration and duration of openings within burst and prolonged the mean closed time. All of these changes contributed to the decrease in the open probability in a concentration-dependent manner. Conclusions: Several aspects of octanol action on neuronal AChRs at the single-channel level are compatible with an atypical open channel block model reported with muscle nicotinic AChRs. The potentiating action of short-chain alcohols and the inhibitory action of long-chain alcohols on the neuronal nicotinic AChR are mediated through different mechanisms. [source]

Spontaneous recurrent network activity in organotypic rat hippocampal slices

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2005
Majid H. Mohajerani
Abstract Organotypic hippocampal slices were prepared from postnatal day 4 rats and maintained in culture for >6 weeks. Cultured slices exhibited from 12 days in vitro spontaneous events which closely resembled giant depolarizing potentials (GDPs) recorded in neonatal hippocampal slices. GDP-like events occurred over the entire hippocampus with a delay of 30,60 ms between two adjacent regions as demonstrated by pair recordings from CA3,CA3, CA3,CA1 and interneurone,CA3 pyramidal cells. As in acute slices, spontaneous recurrent events were generated by the interplay of GABA and glutamate acting on AMPA receptors as they were reversibly blocked by bicuculline and 6,7-dinitroquinoxaline-2,3-dione but not by dl -2-amino-5-phosphonopentaoic acid. The equilibrium potentials for GABA measured in whole cell and gramicidin-perforated patch from interconnected interneurones,CA3 pyramidal cells were ,70 and ,56 mV, respectively. The resting membrane potential estimated from the reversal of N -methyl- d -aspartate-induced single-channel currents in cell-attach experiments was ,75 mV. In spite of its depolarizing action, in the majority of cases GABA was still inhibitory as it blocked the firing of principal cells. The increased level of glutamatergic connectivity certainly contributed to network synchronization and to the development of interictal discharges after prolonged exposure to bicuculline. In spite of its inhibitory action, in a minority of cells GABA was still depolarizing and excitatory as it was able to bring principal cells to fire, suggesting that a certain degree of immaturity is still present in cultured slices. This was in line with the transient bicuculline-induced block of GDPs and with the isoguvacine-induced increase of GDP frequency. [source]

Octanol Modulation of Neuronal Nicotinic Acetylcholine Receptor Single Channels

Loperamide mobilizes intracellular Ca2+ stores in insulin-secreting HIT-T15 cells

BRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2003
Li-Ping He
We have investigated the effects of loperamide on intracellular Ca2+ stores and membrane K+ channels in insulin-secreting hamster insulinoma (HIT-T15) cells. In cell-attached patch-clamp mode, loperamide (3,250 ,M) activated large single-channel currents. The loperamide-activated currents were tentatively identified as Ca2+ -activated K+ channel (KCa) currents based on their single-channel conductance (145 pS), apparent reversal potential, and insensitivity to tolbutamide. Smaller single-channel currents with a conductance (32 pS) indicative of adenosine triphosphate-sensitive K+ channels (KATP channels) were also recorded, but were insensitive to loperamide. Surprisingly, the loperamide-activated currents persisted in the absence of extracellular Ca2+. Yet under these conditions, we still measured loperamide-induced Ca2+ increases. These effects are dose dependent. Loperamide had no effects in the inside-out patch configuration, suggesting that loperamide does not directly activate the channels with large conductance, but does so secondarily to release of Ca2+ from intracellular stores. Carbachol (100 ,M), an agonist of muscarinic receptors, which mediates IP3 -dependent intracellular Ca2+ release, enhanced the effects of loperamide on KCa channels. Both the putative KCa currents and Ca2+ signals induced by loperamide (with ,0' [Ca2+]o) were abolished when the intracellular Ca2+ stores had been emptied by pretreating the cells with either carbachol or thapsigargin, an endoplasmic reticulum Ca2+ -ATPase inhibitor that blocks reuptake of calcium. These data indicate that loperamide in insulin-secreting , -cells evokes intracellular Ca2+ release from IP3 -gated stores and activates membrane currents that appear to be carried by KCa, rather than KATP channels. British Journal of Pharmacology (2003) 139, 351,361. doi:10.1038/sj.bjp.0705263 [source]