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Benzamil Attenuates Osmosensitive OVLT Neuron Excitation by Hyperosmotic NaCl
Author(s) -
Kinsman Brian J,
Browning Kirsteen N.,
Stocker Sean D.
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1235.7
Subject(s) - lamina terminalis , medicine , endocrinology , chemistry , sodium channel , biophysics , neuron , electrophysiology , osmotic concentration , sodium , hypothalamus , biology , neuroscience , organic chemistry
Central hypertonic NaCl infusion increases sympathetic nerve activity, vasopressin secretion, and blood pressure. These responses are eliminated by lesion of osmosensitive sites in the lamina terminalis, including the organum vasculosum of the lamina terminalis (OVLT). Intriguingly, intracerebroventricular pretreatment with benzamil (a non‐voltage dependent sodium channel blocker) also attenuates those responses to central NaCl. Taken together, this suggests benzamil may act on those osmosensitive neurons to attenuate physiologic responses to central NaCl. Therefore, I hypothesized that a benzamil‐sensitive channel/transporter mediates OVLT neuron osmosensitivity to NaCl. I evaluated the effect of benzamil on OVLT neuron excitation in response to hyperosmotic (+15mOsm) or isosmotic (+0mOsm) elevations in bath NaCl using whole‐cell recordings of adult rat OVLT neurons in slices. Initially, I measured changes in action potential (AP) discharge frequency with 295mOsm isosmotic, 310mOsm hyperosmotic and 310mOsm + 50μM benzamil bath perfusates. Osmosensitive OVLT neuron (n=14) peak AP discharge increased significantly from a 295mOsm baseline (0.41±0.08 Hz) to 310mOsm (0.94±0.11 Hz; p <0.05), but decreased significantly in response to sequential addition of 50μM benzamil to the 310mOsm perfusate (0.50±0.09 Hz; p <0.05). To assess the effects of benzamil on basal activity, I tested isosmotic 50μM benzamil on a separate set of osmosensitive OVLT neurons (n=9). Isosmotic 50μM benzamil biphasically increased AP discharge from 0.41±0.23 Hz to 0.77±0.34 Hz ( p <0.05 compared to baseline), and then decreased AP discharge to 0.18±0.07 Hz ( p >0.05 compared to baseline). Concomitantly, isosmotic 50μM benzamil depolarized neuron membrane potentials from −51.3±0.77 mV to −46.6±1.4 mV ( p <0.05), and decreased the magnitude of neuron AP after hyperpolarizations from 6.85±0.42 mV to 2.67±0.44 mV ( p <0.05). Injection of hyperpolarizing current pulses revealed that isosmotic 50μM benzamil also increases osmosensitive OVLT neuron input resistance (n=6) from 1228±148 MΩ to 1443±157 MΩ ( p <0.05). These data demonstrate that high‐dose (50μM) benzamil in isosmotic NaCl exerts complex effects on OVLT neuron basal electrophysiology due to its multiple sodium channel/transporter targets. Still, 50μM benzamil does attenuate excitation of OVLT neurons by hyperosmotic NaCl. This data indicates that a benzamil‐sensitive protein contributes to the sodium‐/osmo‐ sensory function of OVLT neurons.