Persistent sodium current, membrane properties and bursting behavior of pre-bötzinger complex inspiratory neurons in vitro.
We measured persistent Na(+) current and membrane properties of bursting-pacemaker and nonbursting inspiratory neurons of the neonatal rat pre-Bötzinger complex (pre-BötC) in brain stem slice preparations with a rhythmically active respiratory network in vitro. In whole-cell recordings, slow voltage ramps (</=100 mV/s) inactivated the fast, spike-generating Na(+) current and yielded N-shaped current-voltage relationships with nonmonotonic, negative-slope regions between -60 and -35 mV when the voltage-sensitive component was isolated. The underlying current was a TTX-sensitive persistent Na(+) current (I(NaP)) since the inward current was present at slow voltage ramp speeds (3.3-100 mV/s) and the current was blocked by 1 microM TTX. We measured the biophysical properties of I(NaP) after subtracting the voltage-insensitive "leak" current (I(Leak)) in the presence of Cd(2+) and in some cases tetraethylammonium (TEA). Peak I(NaP) ranged from -50 to -200 pA at a membrane potential of -30 mV. Decreasing the speed of the voltage ramp caused time-dependent I(NaP) inactivation, but this current was present at ramp speeds as low as 3.3 mV/s. I(NaP) activated at -60 mV and obtained half-maximal activation near -40 mV. The subthreshold voltage dependence and slow inactivation kinetics of I(NaP), which closely resemble those of I(NaP) mathematically modeled as a burst-generation mechanism in pacemaker neurons of the pre-BötC, suggest that I(NaP) predominantly influences bursting dynamics of pre-BötC inspiratory pacemaker neurons in vitro. We also found that the ratio of persistent Na(+) conductance to leak conductance (g(NaP)/g(Leak)) can distinguish the phenotypic subpopulations of bursting pacemaker and nonbursting inspiratory neurons: pacemaker neurons showed g(NaP)/g(Leak) > g(NaP)/g(Leak) in nonpacemaker cells (P < 0.0002). We conclude that I(NaP) is ubiquitously expressed by pre-BötC inspiratory neurons and that bursting pacemaker behavior within the heterogeneous population of inspiratory neurons is achieved with specific ratios of these two conductances, g(NaP) and g(Leak).
Del Negro
Christopher A
CA
Cellular and Systems Neurobiology Section, Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4455, USA.
Koshiya
Naohiro
N
Butera
Robert J
RJ
Smith
Jeffrey C
JC
D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D002118:Calcium / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010641:Phenotype; D051381:Rats; D012125:Respiratory Center / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D015222:Sodium Channels / Q000502:physiology*; D013569:Synapses / Q000502:physiology
D015222:Sodium Channels; D002118:Calcium