Ionic basis of the caesium-induced depolarisation in rat supraoptic nucleus neurones.
1. The effects of external Cs(+) on magnocellular neurosecretory cells were studied during intracellular recordings from 93 supraoptic nucleus neurones in superfused explants of rat hypothalamus. 2. Bath application of 3-5 mM Cs(+) provoked reversible membrane depolarisation and increased firing rate in all of the neurones tested. Voltage-current analysis revealed an increase in membrane resistance between -120 and -55 mV. The increase in resistance was greater below -85 mV than at more positive potentials. 3. Voltage-clamp analysis showed that external Cs(+) blocked the hyperpolarisation-activated inward current, I(H). Under current clamp, application of ZD 7288, a selective blocker of I(H), caused an increase in membrane resistance at voltages < or = -65 mV. Voltage-current analysis further revealed that blockade of I(H) caused hyperpolarisation when the initial voltage was < -60 mV but had no effect at more positive values. 4. Current- and voltage-clamp analysis of the effects of Cs(+) in the presence of ZD 7288, or ZD 7288 and tetraethyl ammonium (TEA), revealed an increase in membrane resistance throughout the range of voltages tested (-120 to -45 mV). The current blocked by Cs(+) in the absence of I(H) was essentially voltage independent and reversed at -100 mV. The reversal potential shifted by +22.7 mV when external [K(+)] was increased from 3 to 9 mM. We conclude that, in addition to blocking I(H), external Cs(+) blocks a leakage K(+) current that contributes significantly to the resting potential of rat magnocellular neurosecretory cells.
Ghamari-Langroudi
M
M
Centre for Research in Neuroscience, Montreal General Hospital and McGill University, 1650 Cedar Avenue, Montreal, QC, Canada H3G 1A4.
Bourque
C W
CW
D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology*; D004594:Electrophysiology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D020318:Rats, Long-Evans; D013495:Supraoptic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D002316:Cardiotonic Agents; D015221:Potassium Channels; D011743:Pyrimidines; C082246:ICI D2788; D002586:Cesium