D-glucose-sensitive neurosecretory cells of the crab Cancer borealis and negative feedback regulation of blood glucose level.
We studied the effects of glucose on cultured X-organ neurons of the crab Cancer borealis using single-electrode current- and voltage-clamp techniques. A subpopulation of the cells responded to D-glucose with a hyperpolarization. These cells, but not glucose-insensitive cells, showed immunoreactivity to crustacean hyperglycemic hormone (CHH), the hormone responsible for the elevation of blood glucose levels in crustaceans. Glucose-sensitive cells were also inhibited by serotonin and gamma-aminobutyric acid but were not affected by dopamine and Leu-enkephalin. The response was specific for D-glucose, with an EC50 of 0.25 mmoll-1. No response was seen to L-glucose, sucrose, galactose, mannose or fructose. The glucose response persisted in the absence of extracellular Na+ and in low-Ca2+/Mn2+ saline. In voltage-clamp experiments, D-glucose evoked a small current with a reversal potential close to that of voltage-dependent K+ currents. We conclude that D-glucose activates a K+ current in CHH-immunoreactive cells that, in normal saline, induces a hyperpolarization. We propose that this enables glucose to regulate directly the release of CHH into the hemolymph, thus constituting a negative feedback mechanism regulating hemolymph glucose concentration.
Glowik
R M
RM
Volen Center, Brandeis University, Waltham, MA 02254, USA.
Golowasch
J
J
Keller
R
R
Marder
E
E
D000818:Animals; D001786:Blood Glucose / Q000502:physiology*; D003386:Brachyura / Q000502:physiology*; D004594:Electrophysiology; D005947:Glucose / Q000494:pharmacology; D009490:Neurosecretory Systems / Q000502:physiology*
D001786:Blood Glucose; D005947:Glucose