Inhibition by wortmannin of M-current in bullfrog sympathetic neurones.
1. The actions of wortmannin, an inhibitor of myosin light chain kinase (MLCK), on M-type potassium current of dissociated bullfrog sympathetic neurones have been examined. 2. The amplitude of M-current was measured by whole cell recordings from cells pretreated with wortmannin (0.01-10 microM) or the wortmannin vehicle, dimethylsulphoxide (0.0001-0.1 vol%), for 30 min. Internal (recording pipette) solutions having three different pCa values (6, 7 and 8) were used for the measurements. 3. Irrespective of the pCa, M-current was not detectable when the cells were pretreated with 10 microM wortmannin. Wortmannin, 3 microM, produced 85-95% inhibition of the M-current. Pretreatment with 10-30 nM wortmannin was without effect on M-current. 4. The M-current inhibition by wortmannin at concentrations of 0.1-1 microM depended on the pCa of the internal solution. Inhibition occurred only when the calcium-rich (pCa = 6) internal solution was used. 5. Pre-treatment of the cells with wortmannin (10 microM) did not affect rapidly-inactivating A-type or delayed rectifier-type potassium currents not did it alter inwardly rectifying sodium-potassium current (IH). 6. These observations show that M-current inhibition by wortmannin has two pharmacological profiles. One is calcium-dependent and occurs at lower concentrations (0.1-1 microM), and is attributed to inhibition of MLCK by wortmannin. At higher concentrations (3-10 microM), wortmannin has an additional, calcium-independent action, inhibiting the M-current by an unknown mechanism.
Tokimasa
T
T
Department of Physiology, Kurume University School of Medicine, Japan.
Ito
M
M
Simmons
M A
MA
Schneider
C R
CR
Tanaka
T
T
Nakano
T
T
Akasu
T
T
D000730:Androstadienes / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D002147:Calmodulin / Q000494:pharmacology; D046508:Culture Techniques; D000242:Cyclic AMP / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D011892:Rana catesbeiana; D013564:Sympathetic Nervous System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000077191:Wortmannin
D000730:Androstadienes; D002147:Calmodulin; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D000242:Cyclic AMP; D009219:Myosin-Light-Chain Kinase; D002118:Calcium; D000077191:Wortmannin