Actions of baclofen on components of the Ca-current in rat and mouse DRG neurones in culture.
1. Ca currents in rat and mouse sensory dorsal root ganglion (DRG) neurones were inhibited by concentrations of (-)-baclofen as low as 1 micron. The proportion of neurones responding to baclofen was low (less than 20%), except in young cultures of neonate rat DRG neurones (3 days in culture), where 86% of the neurones were responsive. 2. Three types of unitary Ca currents were observed in the rat DRG neurones, corresponding to the T-, N- and L-type currents of chick DRG neurones. 3. Baclofen produced two types of response on whole-cell currents of DRG neurones from both species. The first was on an early inactivating component of the Ca current. This early current was partially inactivated at a holding potential of -40 mV. It was also reduced during the second of a pair of depolarizing command pulses. The results suggest that this action of baclofen is due to an action on an N-type component of the current. The second response to baclofen persisted throughout the command step and was not reduced during the second of a pair of command pulses, indicating that this effect is due to an action on the L-type current. 4. Unitary or ensemble Ca currents recorded in cell-attached patches, on neurones previously shown to respond to baclofen in whole-cell clamp mode, were generally not inhibited by baclofen application external to the patch electrode. This indicates that a readily diffusible internal second messenger substance is probably not involved in coupling the GABAB receptor to the ion channels.
Green
K A
KA
MRC Neurosciences Group, University of St Andrews, Fife.
Cottrell
G A
GA
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001418:Baclofen / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D005727:Ganglia, Spinal / Q000166:cytology / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects*; D051379:Mice; D009474:Neurons / Q000187:drug effects*
D007473:Ion Channels; D001224:Aspartic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D001418:Baclofen; D002118:Calcium