Biomedical subjects

A A Selyanko

Publications and source records attributed to A A Selyanko.

At least 19 recordsLinked to original sources

PubMed2002

Dominant-negative subunits reveal potassium channel families that contribute to M-like potassium currents.

M-currents are K+ currents generated by members of the KCNQ family of K+ channels (Wang et al., 1998). However, in some cells, M-like currents may be contaminated by members of other K+ channel gene families, such as the erg family (Meves et al., 1999; Selyanko et al., 1999). In the present experiments, we have used the acute expression of pore-defective mutants of KCNQ3 (DN-KCNQ3) and Merg1a (DN-Merg1a) as dominant negatives to separate the contributions of these two families to M-like currents in NG108-15 neuroblastoma hybrid cells and rat sympathetic neurons. Two kinetically and pharmacologically separable components of M-like current could be recorded from NG108-15 cells that were individually suppressed by DN-Merg1a and DN-KCNQ3, respectively. In contrast, only DN-KCNQ3, and not DN-Merg1a, reduced currents recorded from sympathetic neurons. Pharmacological tests suggested that the residual current in DN-KCNQ3-treated sympathetic neurons was carried by residual KCNQ channels. Ineffectiveness of DN-Merg1a in sympathetic neurons was not caused by lack of expression, as judged by confocal microscopy of Flag-tagged DN-Merg1a. These results accord with previous inferences regarding the roles of erg and KCNQ channels in generating M-like currents. This experimental approach should therefore be useful in delineating the contributions of members of these two gene families to K+ currents in other cells.

Animals↗

PubMed2001

Properties of single M-type KCNQ2/KCNQ3 potassium channels expressed in mammalian cells.

1. The single channel properties of KCNQ2/KCNQ3 channels underlying neuronal voltage-dependent M-type potassium currents were studied in cell-attached patches from transfected Chinese hamster ovary (CHO) cells. Macroscopic currents produced by homo- and heteromeric KCNQ2/KCNQ3 channels were measured using the perforated-patch whole-cell technique. 2. Compared with heteromeric KCNQ2 + KCNQ3 channels, homomeric KCNQ2 channels had lower slope conductance (9.0 +/- 0.3 and 5.8 +/- 0.3 pS, respectively) and open probability at 0 mV (0.30 +/- 0.07 and 0.15 +/- 0.03, respectively), consistent with their 3.8-fold smaller macroscopic currents. By contrast, homomeric KCNQ3 channels had the same slope conductance (9.0 +/- 1.1 pS) as KCNQ2 + KCNQ3 channels, and higher open probability (0.59 +/- 0.11), inconsistent with their 12.7-fold smaller macroscopic currents. Thus, KCNQ2 and KCNQ3 subunits may play different roles in the expression of M-type currents, with KCNQ2 ensuring surface expression of underlying channels and KCNQ3 modifying their function. 3. Both in homo- and heteromeric KCNQ2/KCNQ3 channels the shut time distributions were fitted with three, and the open time distributions with two, exponential components. By measuring these and other parameters (e.g. conductance and open probability) KCNQ2/ KCNQ3 channels can be shown to resemble previously characterised neuronal M-type channels.

Animals↗

PubMed2001

Alternative splicing of KCNQ2 potassium channel transcripts contributes to the functional diversity of M-currents.

The region of alternative splicing in the KCNQ2 potassium channel gene was determined by RNase protection analysis of KCNQ2 mRNA transcripts. Systematic analysis of KCNQ2 alternative splice variant expression in rat superior cervical ganglia revealed multiple variant isoforms. One class of KCNQ2 splice variants, those that contained exon 15a, was found to have significantly different kinetics to those of the other isoforms. These transcripts encoded channel subunits that, when co-expressed with the KCNQ3 subunit, activated and deactivated approximately 2.5 times more slowly than other isoforms. Deletion of exon 15a in these isoforms produced a reversion to the faster kinetics. Comparison of the kinetic properties of the cloned channel splice variants with those of the native M-current suggests that alternative splicing of the KCNQ2 gene may contribute to the variation in M-current kinetics seen in vivo.

Alternative Splicing↗

PubMed2000

Inhibition of KCNQ1-4 potassium channels expressed in mammalian cells via M1 muscarinic acetylcholine receptors.

1. KCNQ1-4 potassium channels were expressed in mammalian Chinese hamster ovary (CHO) cells stably transfected with M1 muscarinic acetylcholine receptors and currents were recorded using the whole-cell perforated patch technique and cell-attached patch recording. 2. Stimulation of M1 receptors by 10 microM oxotremorine-M (Oxo-M) strongly reduced (to 0-10%) currents produced by KCNQ1-4 subunits expressed individually and also those produced by KCNQ2 + KCNQ3 and KCNQ1 + KCNE1 heteromers, which are thought to generate neuronal M-currents (IK,M) and cardiac slow delayed rectifier currents (IK,s), respectively. 3. The activity of KCNQ2 + KCNQ3, KCNQ2 and KCNQ3 channels recorded with cell-attached pipettes was strongly and reversibly reduced by Oxo-M applied to the extra-patch membrane. 4. It is concluded that M1 receptors couple to all known KCNQ subunits and that inhibition of KCNQ2 + KCNQ3 channels, like that of native M-channels, requires a diffusible second messenger.

Animals↗

PubMed2000

Differential tetraethylammonium sensitivity of KCNQ1-4 potassium channels.

In Shaker-group potassium channels the presence of a tyrosine residue, just downstream of the pore signature sequence GYG, determines sensitivity to tetraethylammonium (TEA). The KCNQ family of channels has a variety of amino acid residues in the equivalent position. We studied the effect of TEA on currents generated by KCNQ homomers and heteromers expressed in CHO cells. We used wild-type KCNQ1-4 channels and heteromeric KCNQ2/3 channels incorporating either wild-type KCNQ3 subunits or a mutated KCNQ3 in which tyrosine replaced threonine at position 323 (mutant T323Y). IC50 values were (mM): KCNQ1, 5.0; KCNQ2, 0.3; KCNQ3, > 30; KCNQ4, 3.0; KCNQ2 + KCNQ3, 3.8; and KCNQ2 + KCNQ3(T323Y), 0.5. While the high TEA sensitivity of KCNQ2 may be conferred by a tyrosine residue lacking in the other channels, the intermediate TEA sensitivity of KCNQ1 and KCNQ4 implies that other residues are also important in determining TEA block of the KCNQ channels.

Amino Acid Substitution↗

PubMed1999

Two types of K(+) channel subunit, Erg1 and KCNQ2/3, contribute to the M-like current in a mammalian neuronal cell.

The potassium M current was originally identified in sympathetic ganglion cells, and analogous currents have been reported in some central neurons and also in some neural cell lines. It has recently been suggested that the M channel in sympathetic neurons comprises a heteromultimer of KCNQ2 and KCNQ3 (Wang et al., 1998) but it is unclear whether all other M-like currents are generated by these channels. Here we report that the M-like current previously described in NG108-15 mouse neuroblastoma x rat glioma cells has two components, "fast" and "slow", that may be differentiated kinetically and pharmacologically. We provide evidence from PCR analysis and expression studies to indicate that these two components are mediated by two distinct molecular species of K(+) channel: the fast component resembles that in sympathetic ganglia and is probably carried by KCNQ2/3 channels, whereas the slow component appears to be carried by merg1a channels. Thus, the channels generating M-like currents in different cells may be heterogeneous in molecular composition.

Animals↗

PubMed1999

The role of ryanodine receptors in the cyclic ADP ribose modulation of the M-like current in rodent m1 muscarinic receptor-transformed NG108-15 cells.

1. The role of cyclic ADP ribose and ryanodine receptors in the inhibition of the M-like current (IK(M,ng)) by acetylcholine was investigated in m1 muscarinic receptor-transformed mouse neuroblastoma-rat glioma hybrid (NG108-15) cells using patch-clamp techniques and calcium microfluorimetry. 2. Acetylcholine (1-100 microM) decreased IK(M,ng) by up to 55 %. Application, via the patch pipette, of the cyclic ADP ribose antagonists 8-amino-cyclic ADP ribose (10-100 microM) and 8-bromo-cyclic ADP ribose (100-1000 microM) reduced this inhibition of IK(M,ng) in a concentration-dependent manner. The half-maximal inhibition concentrations for 8-amino- cyclic ADP ribose and 8-bromo-cyclic ADP ribose were around 40 microM and 1 mM, respectively. 3. Neither of the cyclic ADP ribose antagonists altered the amplitude of IK(M,ng) per se, or the incidence of the concurrent Ca2+-activated K+ current (IIK(Ca)) activation, also mediated by acetylcholine. 4. The ryanodine receptor modulators ryanodine (1-10 microM) and Ruthenium Red (10 microM) did not alter IK(M,ng) amplitude or IK(M,ng) inhibition mediated by acetylcholine. There was a statistically significant increase in the proportion of cells showing outward currents in the presence of Ruthenium Red. 5. Intracellular calcium levels measured with fura-2 microfluorimetry were increased with low concentrations of ryanodine (1 microM), more consistently with caffeine (10 mM), and in almost every case with both bradykinin (300 nM) and acetylcholine (100 microM). Caffeine-, but not bradykinin-evoked responses were abolished by preincubation with ryanodine (10 microM). 6. The fast 'rundown rate' of the M-current recorded in rat superior cervical ganglion cells under whole-cell conditions precluded an investigation of the effects of intracellular dialysis of cyclic ADP ribose. However, when cyclic ADP ribose (5 microM) was applied directly to the cytoplasmic face of inside-out membrane patches excised from rat superior cervical ganglion cells containing M-channels, it had no effect on the main parameters of single channel activity (conductance, mean open time or frequency of opening). 7. These results indicate that cyclic ADP ribose acts on a specific intracellular site to mediate IK(M,ng) inhibition. However, unlike previously established effects of cyclic ADP ribose, the ryanodine receptor is not required, suggesting that another molecular target may be involved. Studies at the single channel level indicate that cyclic ADP ribose may not act directly on the M-channels in inside-out patches.

Acetylcholine↗

PubMed1999

M-channel gating and simulation.

Single potassium M-channels in rat sympathetic neurons have multiple voltage-dependent kinetic components in their activity: short, medium, and long closed times (tau(CS), tau(CM), and tau(CL)) and short and long open times (tau(OS) and tau(OL)). All five components can be detected in cell-attached patches, but only four of them (tau(CS), tau(CM), tau(OS), and tau(OL)) in excised patches (, J. Physiol. (Lond.). 472:711-724; 1996, Neuron. 16:151-162; 1996, Neuropharmacology. 35:933-947). Analysis of the burst structure of activity recorded from cell-attached and excised inside-out patches showed it to be consistent with the sequential kinetic scheme C(L) left arrow over right arrow O(S) left arrow over right arrow C(M) left arrow over right arrow O(L) left arrow over right arrow C(S). Using this scheme and experimentally determined kinetic parameters, we successfully simulated the activity of M-channels both under steady-state conditions and during depolarizing voltage steps. Consistent with the characteristic behavior of macroscopic M-current, ensemble currents constructed from simulated M-channels had exponential activation and deactivation, with no delays, when tested in the range between -50 and -20 mV.

Animals↗

PubMed1998

Ca2+-inhibited non-inactivating K+ channels in cultured rat hippocampal pyramidal neurones.

1. Whole-cell perforated-patch recording from cultured CA1-CA3 pyramidal neurones from neonatal rat hippocampus (20-22 C; [K+]o = 2.5 mM) revealed two previously recorded non-inactivating (sustained) K+ outward currents: a voltage-independent 'leak' current (Ileak) operating at all negative potentials, and, at potentials >= -60 mV, a time- and voltage-dependent 'M-current' (IK(M)). Both were inhibited by 1 mM Ba2+ or 10 microM oxotremorine-M (Oxo-M). In ruptured-patch recording using Ca2+-free pipette solution, Ileak was strongly enhanced, and was inhibited by 1 mM Ba2+ but unaffected by 0.5 mM 4-aminopyridine (4-AP), 1 mM tetraethylammonium (TEA) or 1-10 nM margatoxin. 2. Single channels underlying these currents were sought in cell-attached patch recordings. A single class of channels of conductance approximately 7 pS showing sustained activity at resting potential and above was identified. These normally had a very low open probability (Po < 0. 1), which, however, showed a dramatic and reversible increase (to about 0.9 at approximately 0 mV) following the removal of Ca2+ from the bath. Under these (Ca2+-free) conditions, single-channel Po showed both voltage-dependent and voltage-independent components on patch depolarization from resting potential. The mean activation curve was fitted by a modified Boltzmann equation. When tested, all channels were reversibly inhibited by addition of 10 microM Oxo-M to the bath solution. 3. The channels maintained their high Po in patches excised in inside-out mode into a Ca2+-free internal solution and were strongly inhibited by application of Ca2+ to the inner face of the membrane (IC50 = 122 nM); this inhibition was observed in the absence of MgATP, and therefore was direct and unrelated to channel phosphorylation/dephosphorylation. 4. Channels in patches excised in outside-out mode were blocked by 1 mM Ba2+ but were unaffected by 4-AP or TEA. 5. Channels in cell-attached patches were inhibited after single spikes, yielding inward ensemble currents lasting several hundred milliseconds. This was prevented in Ca2+-free solution, implying that it was due to Ca2+ entry. 6. The properties of these channels (block by internal Ca2+ and external Oxo-M and Ba2+, and the presence of both voltage-dependent and voltage-independent components in their Po/V relationship) show points of resemblance to those expected for channels associated with both Ileak and IK(M) components of the sustained macroscopic currents. For this reason we designate them Ksust ('sustained current') channels. Inhibition of these channels by Ca2+ entry during an action potential may account for some forms of Ca2+-dependent after-depolarization. Their high sensitivity to internal Ca2+ may provide a new, positive feedback mechanism for cell excitation operating at low (near-resting) [Ca2+]i.

Animals↗

PubMed1998

Small (SKCa) Ca2+-activated K+ channels in cultured rat hippocampal pyramidal neurones.

Small (SKCa) Ca2+-activated K+ channels were identified in membrane patches excised from cultured CA1-CA3 pyramidal neurones of the neonatal rat hippocampus. When recorded in low-K+ extracellular solution ([K+]o=2.5 mM), SKCa channels had a low conductance (@3 pS at 0 mV), were activated by >/=175 nM Ca2+ (Po=0.54 at 500 nM Ca2+) and there were two open-time components (2.1 and @70 ms) to their activity. These properties of single SKCa channels are similar to those of slow after-hyperpolarization channels (sAHP) previously inferred from fluctuation analysis of the sAHP current. It is concluded that the SKCa channel reported here may be the channel that generates the sAHP in hippocampal pyramidal neurones.

Animals↗

PubMed1997

Muscarinic mechanisms in nerve cells.

The receptor subtype and transduction mechanisms involved in the regulation of various neuronal ionic currents are reviewed, with some recent observations on sympathetic neurons, hippocampal cell membranes and basal forebrain cells.

Animals↗

PubMed1997

Effects of a cognition-enhancer, linopirdine (DuP 996), on M-type potassium currents (IK(M)) and some other voltage- and ligand-gated membrane currents in rat sympathetic neurons.

Linopirdine is a cognition enhancer which augments depolarization-induced transmitter release in the cortex and which is under consideration for potential treatment of Alzheimer's disease. It has previously been reported to inhibit M-type K+ currents in rat hippocampal neurons. In the present experiments we have tested its effect on whole-cell M-currents and single M-channels, and on a range of other membrane currents, in dissociated rat superior cervical sympathetic ganglion cells. Linopirdine inhibited the whole-cell M-current with an IC50 of 3.4 microM and blocked M-channels recorded in excised outside-out membrane patches but not in inside-out patches. This suggests that linopirdine directly blocks M-channels from the outside. It was much less effective in inhibiting other voltage-gated potassium currents [delayed rectifier (IK(V)), IC50 63 microM; transient (IA) current, IC50 69 microM] and produced no detectable inhibition of the fast and slow Ca(2+)-activated K+ currents IC and IAHP or of a hyperpolarization-activated cation current (IQ/Ih) at 10-30 microM. However, it reduced acetylcholine-activated nicotinic currents and GABA-activated Cl- currents with IC50 values of 7.6 and 26 microM respectively. It is concluded that linopirdine shows some 20-fold selectivity for M-channels among different K+ channels but can also block some transmitter-gated channels. The relationship between M-channel block and the central actions of linopirdine are discussed.

Animals↗

PubMed1996

Regulation of M-type potassium channels in mammalian sympathetic neurons: action of intracellular calcium on single channel currents.

Currents through single M-type potassium channels were recorded in membrane patches excised from rat superior cervical sympathetic neurons. Application of Ca+ to the internal face of inside-out patches produce two forms of M-channel inhibition: a slow, all-or-nothing suppression of activity; and a fast block associated with a concentration-dependent shortening of open times compatible with open-channel block. Both forms of block were enhanced by patch depolarization. Neither was replicated or affected by Mg2+, and both could be recorded in the absence of intracellular ATP, implying that they did not involve phosphorylation. Since the block was reversible in the absence of ATP and since alkaline phosphatase did not reduce channel activity, block was unlikely to have resulted from dephosphorylation. In cell-attached patch recording, M-channel activity increased during exposure of the cell to Ca2(+)-free solution and was rapidly reduced on applying 2mM Ca2+ to the extra-patch solution. This suggests that M-channel activity in these neurons may be tonically regulated by variations in resting intracellular [Ca2+].

Adenosine Triphosphate↗

PubMed1996

Intracellular calcium directly inhibits potassium M channels in excised membrane patches from rat sympathetic neurons.

Complex effects of altering intracellular [Ca2+] on M-type K+ currents have previously been reported using whole-cell current recording. To study the direct effect of Ca2+ on M-channel activity, we have applied Ca2+ to the inside face of membrane patches excised from rat superior cervical sympathetic ganglion cells. Ca2+ rapidly and reversibly inhibited M-channel activity in 28/44 patches by up to 87%, with a mean IC50 of 100 nM. This effect persisted in the absence of ATP, implying that it was not due to phosphorylation/dephosphorylation. A similar effect was observed in 13/13 cell-attached patches when cells were transiently "Ca(2+)-loaded" by adding 2 mM Ca2+ to a 25 mM K+ solution bathing the extrapatch cell membrane. These observations provide new evidence that Ca2+ can directly inhibit M channels, so supporting the view that Ca2+ might mediate M current inhibition following muscarinic receptor activation.

Adenosine Triphosphate↗

PubMed1995

Putative M-type potassium channels in neuroblastoma-glioma hybrid cells: inhibition by muscarine and bradykinin.

Putative M-type K(+)-channels ('M-channels') were recorded in differentiated NG108-15 neuroblastoma x glioma hybrid cells transformed to express m1 muscarinic acetylcholine receptors using cell-attached patch-electrodes. Channels showed multiple conductances, with peaks at 6-9 and 12-15 pS. Averaged currents showed time-dependent activation during 1 s depolarization steps to around -30 mV. Steady-state Po increased in a voltage-dependent manner when the membrane was depolarized between 10 and 60 mV, with a limiting slope of 5.5 mV/e-fold change in Po. Steady-state kinetics were fit by two open and three shut times: depolarization shortened shut times and lengthened open times. Application of muscarine (10 microM) or bradykinin (10 microM) to the membrane outside the patch reversibly reduced steady-state in-patch channel activity to 38.4 +/- 11.7 and 28.8 +/- 6.1% of control values, respectively. Inhibition was accompanied by a lengthening of channel shut times without significant change in open times or distribution of conductance levels. No effect of muscarine or bradykinin on whole-cell or membrane patch delayed rectifier currents was detected. It is concluded that M-channels in NG108-15 cells are qualitatively similar to, but sparser than, those previously reported in rat sympathetic neurones. Their inhibition by extra-patch acetylcholine and bradykinin suggests that a mobile messenger is involved in the transduction process leading from receptor activation to channel closure.

Animals↗

PubMed1994

Activation of nucleotide receptors inhibits M-type K current [IK(M)] in neuroblastoma x glioma hybrid cells.

A phospholipase-C-linked nucleotide receptor, sensitive to both uridine and adenosine triphosphate (UTP and ATP) has been cloned from NG108-15 neuroblastoma x glioma hybrid cells. We have tested whether activation of this receptor could inhibit the voltage-dependent K+ current [IK(M) or "M-current"] in NG108-15 cells recorded using whole-cell patch-clamp methods. Both UTP and ATP inhibited IK(M) by 44% and 42%, respectively, at 100 microM. Mean IC50 values were: UTP, 0.77 +/- 0.27 microM; ATP, 1.81 +/- 0.82 microM. The order of nucleotide and nucleoside activity at 100 microM was: UTP = ATP > ATP [gamma S] = ITP > 2-MeSATP > ADP = GTP >> AMP-CPP, adenosine, where ATP[gamma S] is adenosine 5'-O-(3-thiotriphosphate), ITP is inosine 5'-triphosphate, 2-MeSATP is 2-methylthio ATP and AMP-CPP is alpha, beta methylene ATP. This rank order accords with their activities at the cloned P2U receptor. Effects were not inhibited by suramin (up to 500 microM) or by pre-incubation for 12 h in 500 ng.ml-1 Pertussis toxin. Inhibition of IK(M) was frequently preceded by a transient outward current, probably a Ca(2+)-activated K+ current, responding to Ca2+ mobilization. No effect on the delayed rectifier K+ current was observed. These observations match those expected from stimulating other phospholipase-C-linked receptors in NG108-15 cells.

Adenosine Triphosphate↗

PubMed1994

Mechanism of long-lasting block of ganglion nicotinic receptors by mono-ammonium compounds with long aliphatic chain.

The effect of long-chain mono-ammonium compounds (long-chain MACs), t-butyldecylammonium (IEM-1078), 2,2,6,6-tetramethyldecylpiperidine (IEM-1559), and diisopropyldecylammonium (IEM-1194), on nicotinic acetylcholine receptors (nAChRs) was studied in sympathetic ganglion neurons using the patch clamp method. Long-chain MACs (1-10 microM) strongly inhibited acetylcholine (ACh)-induced current (ACh-current); the block persisted for hours after washing the drugs out. Short-chain MACs had a much weaker and completely reversible blocking effect. Suppression of ACh-current by MACs was dose- and voltage-dependent; it was absent at low ACh doses or at potentials > or = 60 mV and increased with higher ACh doses or hyperpolarization. The second of two ACh-currents induced by paired application of ACh was inhibited by long-chain MACs more strongly than the first. This use-dependent block also persisted for hours after washing the drugs out. Additional inhibition of the second ACh-current was reduced by lengthening the time interval between ACh applications in the pair. Time constants of the recovery of the second ACh-current in the presence and after washing out of long-chain MACs were similar, ranging from 45 to 140 s at -50 mV for different long-chain MACs, and decreased with de- or hyperpolarization. The use-dependent block produced by long-chain MACs could be prevented by another long-chain MAC with a small ammonium head (IEM-1195, 75-100 microM) or trimethaphan (30 microM), a competitive antagonist of ACh in ganglia. Neither the short-chain MAC (IEM-1405, 100 microM) nor ACh (100 microM) could exert this protective effect. Long-chain MACs did not exert any use-, dose- or voltage-dependent suppression of ACh-current when applied intracellularly. Single-channel conductance was not affected by IEM-1194 (3-10 microM). We suggest that inhibition of ACh-current by long-chain MACs is accounted for by (i) a long-lasting, apparently irreversible, binding of the drug near the channel of nAChR via its long aliphatic chain and (ii) a slow reversible block of the nAChR channel with the MAC's ammonium head.

Acetylcholine↗

PubMed1993

Effects of membrane potential and muscarine on potassium M-channel kinetics in rat sympathetic neurones.

1. Using cell-attached patch pipettes, sustained activity of single potassium M-channels was recorded from dissociated rat superior cervical ganglion neurones. Previous results indicated that this activity, consisting of three main levels of open-channel conductance (congruent to 7, congruent to 12 and congruent to 19 pS) was activated by membrane depolarization and inhibited by muscarine added outside the patch. Consequently, a kinetic analysis was undertaken in order to identify M-channel states sensitive to muscarine and membrane potential. 2. Channel activity recorded at 30 mV positive to the resting membrane potential level (congruent to -60 mV) showed three shut and two open times. Mean shut times were: tau s1 = 8.0 +/- 2.2 ms; tau s2 = 71.3 +/- 8.6 ms and tau s3 = 740 +/- 220 ms. Mean open times were: tau o1 = 10.6 +/- 1.9 ms and tau o2 = 59.3 +/- 8.7 ms. When bursts of channel openings were determined as those including tau s1, two exponential components were evident in burst duration distributions (tau b1 = 11.0 +/- 0.9 ms and tau b2 = 80.4 +/- 11.0 ms). 3. Membrane hyperpolarization significantly lengthened all three shut times and shortened both open times. It also slightly enhanced the relative contribution of high-conductance channels and decreased the relative contribution of low-conductance channels to overall activity. 4. All three shut times of the M-channels were lengthened by 10 microM muscarine without significantly affecting their open times. 5. It is concluded that both open and shut states of the M-channel are voltage sensitive while only shut states are sensitive to muscarine.

Animals↗