title: Membrane ionic currents and properties of freshly dissociated rat brainstem neurons.
abstract: It is well known that neuronal firing properties are determined by synaptic inputs and inherent membrane functions such as specific ionic currents. To characterize the ionic currents of brainstem cardio-respiratory neurons, cells from the hypoglossal (XII) nucleus and the dorsal motor nucleus of the vagus (DMX) were freshly dissociated and membrane ionic currents were studied under whole-cell voltage and current clamp. Both of these neurons showed a TTX-sensitive Na+ current with a much larger current density in XII than DMX neurons. This Na+ current had two (fast and slow) distinct inactivation decay components. The ratio of the magnitudes of the fast to slow component was roughly two-fold greater in DMX than in XII cells. Both DMX and XII neurons also showed a high voltage-activated Ca2+ current, but this current density was significantly greater (three-fold) in DMX than XII neurons. A relatively small amount of low-voltage activated Ca2+ current was also observed in DMX neurons, but not in the majority of XII cells. A transient and a sustained outward current components were observed in DMX cells, but only sustained currents were present in XII neurons. These outward currents had a reversal potential of about -70 mV with 3 mM external K+ and -30 mV with 25 mM K+, and substitution of K+ with cesium and tetraethylammonium suppressed more than 90% the outward currents, indicating that most outward currents were carried by K+. The transient outward current consisted of two components with one sensitive to 4-aminopyridine and the other to intracellular Ca2+. In XII neurons, BRL 38227 (lemakalim), an ATP-sensitive K+ (KATP) channel activator, increased the sustained K+ currents by 10% of control, and glibenclamide, a KATP channel blocker, decreased the sustained K+ currents by 20%. Evidence for the presence of an inward rectifier K+ current was also obtained from both XII and DMX neurons. These results on XII and DMX neurons indicate that (1) the methods used to dissociate neurons provide a useful means to overcome voltage clamp technical difficulties; (2) ion channel characteristics such as density and biophysical properties of DMX neurons are very different from those of XII neurons; and (3) several newly discovered membrane ionic currents are present in these cells.
authors: Department of Pediatrics (Section of Respiratory Medicine) Yale University School of Medicine, New Haven, CT 06520-8064.
authors: C
authors: C
authors: Jiang
authors: T R
authors: TR
authors: Cummins
authors: G G
authors: GG
authors: Haddad
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001933:Brain Stem / Q000166:cytology / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D004553:Electric Conductivity; D007002:Hypoglossal Nerve / Q000502:physiology; D009474:Neurons / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology*; D013997:Time Factors; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D000255:Adenosine Triphosphate; D012964:Sodium; D011188:Potassium; D002118:Calcium