Maturation and myotonia influence the abundance of cation channels KDR, KIR and CIR differently: a patch-clamp study on mouse interosseus muscle fibres.
To detect cation channels, the expression of which is dependent on the physiological state of muscle, single-channel activities of dissociated fibres of the mouse interosseus muscle were recorded using the patch-clamp technique in the cell-attached mode. Fibres were prepared from juvenile and adult wild-type (WT), from chloride channel-deficient myotonic and from denervated adult WT muscles. In all cases delayed-rectifier K+ channels (KDR) with a unitary conductance of 11 pS were recorded in more than 95% of sarcolemmal patches, but with a low, steady-state open probability. Inwards-rectifying K+ channels (KIR) with a conductance of 31 pS in 140 mM [K+]o were active in about 50% of the membrane patches from WT and in more than 90% of those from myotonic fibres. A hitherto undescribed, inwards-rectifying, cation channel, provisionally termed CIR, with fast kinetics and a unitary conductance of 36 pS, was active in nearly every membrane patch from juvenile mice, both WT and myotonic. The abundance of CIR decreased during development, but was not changed 7 days after denervation of adult WT muscle. Ca(2+)-dependent K+ channels were seen sporadically. Channels with the characteristics of adenosine 5'-triphosphate (ATP)-sensitive K+ channels were recorded frequently upon excision of membrane patches, but remained inactive in most cell-attached recordings. In conclusion, of the investigated ion channels, only KIR was responsive to the activity pattern of adult muscle, whereas CIR was down-regulated during muscle maturation.
Kurtz
R
R
Universität Bielefeld, Germany.
Schirm
T
T
Jockusch
H
H
D000375:Aging / Q000378:metabolism*; D000818:Animals; D018118:Chloride Channels / Q000378:metabolism; D051668:Delayed Rectifier Potassium Channels; D004553:Electric Conductivity; D005260:Female; D006614:Hindlimb; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D009222:Myotonia / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated
C086321:CLC-1 channel; D018118:Chloride Channels; D051668:Delayed Rectifier Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated