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1 Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903-0019; and 2 Departments of Physiology and Biophysics and of Medicine, State University of New York at Stony Brook, Stony Brook, New York 11794-8661
Neurons within cardiorespiratory regions of the rostral ventrolateral medulla (RVLM) have been shown to be excited by local hypoxia. To determine the electrophysiological properties of these excitatory responses to hypoxia, we developed a primary dissociated cell culture system to examine the intrinsic response of RVLM neurons to hypoxia. Neonatal rat neurons plated on medullary astrocyte monolayers were studied using the whole cell perforated patch-clamp technique. Sodium cyanide (NaCN, 0.5-10 mM) was used, and membrane potential (Vm), firing frequency, and input resistance were examined. In 11 of 19 neurons, NaCN produced a Vm depolarization, an increase in firing frequency, and a decrease in input resistance, suggesting the opening of a cation channel. The hypoxic depolarization had a linear dose response and was dependent on baseline Vm, with a greater response at more hyperpolarized Vm. In 8 of 19 neurons, NaCN produced a Vm hyperpolarization, decrease in firing frequency, and variable changes in input resistance. The Vm hyperpolarization exhibited an all-or-none dose response and was independent of baseline Vm. These differential responses to NaCN were retained after synaptic blockade with low Ca2+-high Mg2+ or TTX. Thus hypoxic excitation 1) is maintained in cell culture, 2) is an intrinsic response, and 3) is likely due to the increase in a cation current. These hypoxia-excited neurons are likely candidates to function as central oxygen sensors.
respiratory; sympathetic; sodium cyanide; whole cell perforated patch clamp
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