Physiological and molecular characteristics of rat hypothalamic ventromedial nucleus glucosensing neurons.
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 approximately 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.
Department of Neurology and Neurosciences, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, USA.
Ling
L
Kang
Vanessa H
VH
Routh
Eldo V
EV
Kuzhikandathil
Larry D
LD
Gaspers
Barry E
BE
Levin
D000818:Animals; D019540:Area Under Curve; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D017931:DNA Primers; D005941:Glucokinase / Q000235:genetics; D005947:Glucose / Q000502:physiology*; D007700:Kinetics; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000235:genetics; D009474:Neurons / Q000502:physiology*; D051381:Rats; D011930:Reaction Time; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology*
D017931:DNA Primers; D009004:Monosaccharide Transport Proteins; D005941:Glucokinase; D005947:Glucose; D002118:Calcium