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A study of the expression of small conductance calcium-activated potassium channels (SK1-3) in sensory endings of muscle spindles and lanceolate endings of hair follicles in the rat.

ABSTRACT: Processes underlying mechanotransduction and its regulation are poorly understood. Inhibitors of Ca2+-activated K+ channels cause a dramatic increase in afferent output from stretched muscle spindles. We used immunocytochemistry to test for the presence and location of small conductance Ca2+-activated K+ channels (SK1-3) in primary endings of muscle spindles and lanceolate endings of hair follicles in the rat. Tissue sections were double immunolabelled with antibodies to one of the SK channel isoforms and to either synaptophysin (SYN, as a marker of synaptic like vesicles (SLV), present in many mechanosensitive endings) or S100 (a Ca2+-binding protein present in glial cells). SK channel immunoreactivity was also compared to immunolabelling for the Na+ ion channel ASIC2, previously reported in both spindle primary and lanceolate endings. SK1 was not detected in sensory terminals of either muscle spindles or lanceolate endings. SK2 was found in the terminals of both muscle spindles and lanceolate endings, where it colocalised with the SLV marker SYN (spindles and lanceolates) and the satellite glial cell (SGC) marker S100 (lanceolates). SK3 was not detected in muscle spindles; by contrast it was present in hair follicle endings, expressed predominantly in SGCs but perhaps also in the SGC: terminal interface, as judged by colocalisation statistical analysis of SYN and S100 immunoreactivity. The possibility that all three isoforms might be expressed in pre-terminal axons, especially at heminodes, cannot be ruled out. Differential distribution of SK channels is likely to be important in their function of responding to changes in intracellular [Ca2+] thereby modulating mechanosensory transduction by regulating the excitability of the sensory terminals. In particular, the presence of SK2 throughout the sensory terminals of both kinds of mechanoreceptor indicates an important role for an outward Ca2+-activated K+ current in the formation of the receptor potential in both types of ending.

SUBMITTER: Shenton F

PROVIDER: S-EPMC4156425 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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A study of the expression of small conductance calcium-activated potassium channels (SK1-3) in sensory endings of muscle spindles and lanceolate endings of hair follicles in the rat.

Shenton Fiona F Bewick Guy S GS Banks Robert W RW

PloS one 20140905 9

Processes underlying mechanotransduction and its regulation are poorly understood. Inhibitors of Ca2+-activated K+ channels cause a dramatic increase in afferent output from stretched muscle spindles. We used immunocytochemistry to test for the presence and location of small conductance Ca2+-activated K+ channels (SK1-3) in primary endings of muscle spindles and lanceolate endings of hair follicles in the rat. Tissue sections were double immunolabelled with antibodies to one of the SK channel is ...[more]

PMID: 25191752

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Project description:Background and purposeControlling vascular tone involves K(+) efflux through endothelial cell small- and intermediate-conductance calcium-activated potassium channels (K(Ca)2.3 and K(Ca)3.1, respectively). We investigated the expression of these channels in astrocytes and the possibility that, by a similar mechanism, they might contribute to neurovascular coupling.Experimental approachTransgenic mice expressing enhanced green fluorescent protein (eGFP) in astrocytes were used to assess K(Ca)2.3 and K(Ca)3.1 expression by immunohistochemistry and RT-PCR. K(Ca) currents in eGFP-positive astrocytes were determined in situ using whole-cell patch clamp electrophysiology. The contribution of K(Ca)3.1 to neurovascular coupling was investigated in pharmacological experiments using electrical field stimulation (EFS) to evoke parenchymal arteriole dilatation in FVB/NJ mouse brain slices and whisker stimulation to evoke changes in cerebral blood flow in vivo, measured by laser Doppler flowmetry.Key resultsK(Ca)3.1 immunoreactivity was restricted to astrocyte processes and endfeet and RT-PCR confirmed astrocytic K(Ca)2.3 and K(Ca)3.1 mRNA expression. With 200 nM [Ca(2+)](i) , the K(Ca)2.1-2.3/K(Ca)3.1 opener NS309 increased whole-cell currents. CyPPA, a K(Ca)2.2/K(Ca)2.3 opener, was without effect. With 1 µM [Ca(2+)](i) , the K(Ca)3.1 inhibitor TRAM-34 reduced currents whereas apamin (K(Ca)2.1-2.3 blocker) had no effect. CyPPA also inhibited currents evoked by NS309 in HEK293 cells expressing K(Ca)3.1. EFS-evoked Fluo-4 fluorescence confirmed astrocyte endfoot recruitment into neurovascular coupling. TRAM-34 inhibited EFS-evoked arteriolar dilatation by 50% whereas charybdotoxin, a blocker of K(Ca)3.1 and the large-conductance K(Ca) channel, K(Ca)1.1, inhibited dilatation by 82%. TRAM-34 reduced the cortical hyperaemic response to whisker stimulation by 40%.Conclusion and implicationsAstrocytes express functional K(Ca)3.1 channels, and these contribute to neurovascular coupling.

Project description:1. Nine bis-quinolinyl and bis-quinolinium compounds related to dequalinium, and previously shown to block apamin-sensitive small conductance Ca(2+)-activated K(+) channels (SK(Ca)), have been tested for their inhibitory effects on actions mediated by intermediate conductance Ca(2+)-activated K(+) channels (IK(Ca)) in rabbit blood cells. 2. In most experiments, a K(+)-sensitive electrode was employed to monitor the IK(Ca)-mediated net loss of cell K(+) that followed the addition of the Ca(2+) ionophore A23187 (2 microM) to red cells suspended at an haematocrit of 1% in a low K(+) (0.12 - 0.17 mM) solution. The remainder used an optical method based on measuring the reduction in light transmission that occurred on applying A23187 (0.4 or 2 microM) to a very dilute suspension of red cells (haematocrit 0.02%). 3. Of the compounds tested, the most potent IK(Ca) blocker was 1,12 bis[(2-methylquinolin-4-yl)amino]dodecane (UCL 1407) which had an IC(50) of 0.85+/-0.06 microM (mean+/-s.d. mean). 4. The inhibitory action of UCL 1407 and its three most active congeners was characterized by (i) a Hill slope greater than unity, (ii) sensitivity to an increase in external [K(+)], and (iii) a time course of onset that suggested use-dependence. Also, the potency of the nonquaternary compounds tested increased with their predicted lipophilicity. These findings suggested that the IK(Ca) blocking action resembles that of cetiedil rather than of clotrimazole. 5. Some quaternized members of the series were also active. The most potent was the monoquaternary UCL 1440 ((1-[N-[1-(3, 5-dimethoxybenzyl)-2-methylquinolinium-4-yl]amino]-10-[N'-(2-me thylqu inolinium-4yl)amino] decane (trifluoroacetate) which had an IC(50) of 1.8+/-0.1 microM. The corresponding bisquaternary UCL 1438 (1, 10-bis[N-[1-(3,5-dimethoxybenzyl)-2-methylquinolinium-4-yl]amino] decane bis(trifluoroacetate) was almost as active (IC(50) 2.7+/-0.3 microM). 6. A bis-aminoquinolium cyclophane (UCL 1684) had little IK(Ca) blocking action despite its great potency at SK(Ca) channels (IC(50) 4.1+/-0.2 nM). 7. The main outcome is the identification of new intermediate-conductance Ca(2+)-activated K(+) channel blockers with a wide range of IK(Ca)/SK(Ca) selectivities.

Dataset Information

A study of the expression of small conductance calcium-activated potassium channels (SK1-3) in sensory endings of muscle spindles and lanceolate endings of hair follicles in the rat.

Publications

A study of the expression of small conductance calcium-activated potassium channels (SK1-3) in sensory endings of muscle spindles and lanceolate endings of hair follicles in the rat.

Similar Datasets

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