Physiological and Molecular Characteristics of Rat Hypothalamic Ventromedial Nucleus Glucosensing Neurons
Ling Kang 1 ,
Vanessa H. Routh 2 ,
Eldo V. Kuzhikandathil 2 ,
Larry D. Gaspers 2 and
Barry E. Levin 1 3
1 Department of Neurology and Neurosciences, New Jersey Medical School, University of Medicine and Dentistry of New Jersey,
Newark, New Jersey
2 Department of Pharmacology and Physiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey,
Newark, New Jersey
3 Neurology Service, Department of Veterans Affairs New Jersey Health Care System, East Orange, New Jersey
Address correspondence and reprint requests to Barry E. Levin, M.D., Neurology Service (127C), VA Medical Center, 385 Tremont
Ave., East Orange, NJ 07018-1095. E-mail: levin{at}umdnj.edu
Abstract
To evaluate potential mechanisms for neuronal glucosensing, fura-2 Ca 2+ imaging and single-cell RT-PCR were carried out in dissociated ventromedial hypothalamic nucleus (VMN) neurons. Glucose-excited
(GE) neurons increased and glucose-inhibited (GI) neurons decreased intracellular Ca 2+ ([Ca 2+ ] i ) oscillations as glucose increased from 0.5 to 2.5 mmol/l. The Kir6.2 subunit mRNA of the ATP-sensitive K + channel was expressed in 42% of GE and GI neurons, but only 15% of nonglucosensing (NG) neurons. Glucokinase (GK), the putative
glucosensing gatekeeper, was expressed in 64% of GE, 43% of GI, but only 8% of NG neurons and the GK inhibitor alloxan altered
[Ca 2+ ] i oscillations in ∼75% of GK-expressing GE and GI neurons. Insulin receptor and GLUT4 mRNAs were coexpressed in 75% of GE,
60% of GI, and 40% of NG neurons, although there were no statistically significant intergroup differences. Hexokinase-I, GLUT3,
and lactate dehydrogenase-A and -B were ubiquitous, whereas GLUT2, monocarboxylate transporters-1 and -2, and leptin receptor
and GAD mRNAs were expressed less frequently and without apparent relationship to glucosensing capacity. Thus, although GK
may mediate glucosensing in up to 60% of VMN neurons, other regulatory mechanisms are likely to control glucosensing in the
remaining ones.
AUC, area under the curve
[Ca2+]i, intracellular Ca2+
GABA, γ-aminobutyric acid
GE, glucose excited
GI, glucose inhibited
GK, glucokinase
GKRP, GK regulatory protein
HK-I, hexokinase-I
INS-R, insulin receptor
KATP channel, ATP-sensitive K+ channel
Kir, pore-forming, inwardly rectifying K+ channel
LDH, lactate dehydrogenase
Lepr-b, leptin receptor b
MCT, monocarboxylate transporter
mPCR, multiplex PCR
NG, nonglucosensing
sc-RT-PCR
single-cell RT-PCR
SGLT-1, Na+-d-glucose cotransporter-1
SUR, sulfonylurea receptor
VMN, ventromedial nucleus
Footnotes
Accepted December 5, 2003.
Received September 24, 2003.
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