Outward currents influencing bursting dynamics in guinea pig trigeminal motoneurons.
To initiate and maintain bursts (and plateau potentials) in the presence of serotonin, guinea pig trigeminal motoneurons utilize L-type Ca2+ and persistent Na+ inward currents. However, the intrinsic currents that contribute to burst termination and determine the duration of the interburst interval are unknown. Therefore we investigated the roles of outward currents, whose slow activation is coupled to cytosolic cation (Ca2+ and Na+) accumulation. First we examined a Ca2+-dependent K+ current (IK-Ca) with apamin and Ba2+-substituted, low-Ca2+ solution. Blockade of IK-Ca lengthened burst duration and cycle time but did not abolish bursting. Next we studied the Na+/K+-ATPase pump current (Ip) with cardiac glycosides. In the presence of apamin or low-Ca2+/Ba2+ solution, blocking Ip (with ouabain or strophanthidin) decreased both burst duration and cycle time and ultimately transformed bursting into tonic spiking. We conclude that IK-Ca and Ip contribute to burst termination in trigeminal motoneurons. These currents influence temporal bursting properties such as burst duration and cycle time and may help determine the phasic activity of motoneurons during rhythmic oral-motor behaviors.
del Negro
C A
CA
Department of Physiological Science, University of California, Los Angeles, California 90095-1568, USA.
Hsiao
C F
CF
Chandler
S H
SH
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D001464:Barium / Q000493:pharmacokinetics; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D009046:Motor Neurons / Q000737:chemistry / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D010507:Periodicity; D015221:Potassium Channels / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013327:Strophanthidin / Q000494:pharmacology; D014278:Trigeminal Nuclei / Q000737:chemistry / Q000502:physiology*
D004791:Enzyme Inhibitors; D015221:Potassium Channels; D001030:Apamin; D001464:Barium; D012701:Serotonin; D010042:Ouabain; D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium