Hippocampal hypoglycaemia-activated K+ channels: single-channel analysis of glucose and voltage dependence.
The effect of glucose on kinetics and the voltage-dependent characteristics of glucose-sensitive channels in hippocampal neurons were examined with the cell-attached mode of the patch-clamp technique. Recordings of a 100-pS K+ channel in the presence or absence of glucose demonstrate that the increase in channel open state probability (Po) induced by glucose deprivation (40- to 400-times the control in high-glucose medium) was largely due to a decrease in the global amount of time spent by the channel in a long-lived closed state. The Po value of the same 100-pS channel was also found to increase (by approx. 80-times) following a depolarization of 40 mV from rest, the main factor responsible for this being a dramatic shortening of the long closed-times on depolarization. Another glucose-sensitive channel of smaller conductance (approx. 10 pS) showed a similar dependence of Po on glucose, but different dependence on voltage, with long openings at the same hyperpolarized potentials where the 100-pS channel was almost always closed. Our results indicate that the action of glucose on the kinetics of hippocampal channels closely resembles that of ATP-sensitive channels in pancreatic beta-cells. Furthermore, they indicate that the two types of glucose-sensitive channels found in hippocampal neurons, differing not only in their single-channel conductance but also in the dependence on voltage, could play different roles in the responses of these cells to modified energetic supply.
Tromba
C
C
Center of Neuropharmacology, University of Milan, Italy.
Salvaggio
A
A
Racagni
G
G
Volterra
A
A
D000818:Animals; D002478:Cells, Cultured; D004594:Electrophysiology; D005947:Glucose / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D007003:Hypoglycemia / Q000378:metabolism*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
D015221:Potassium Channels; D005947:Glucose