Ion channels of glucose-responsive and -unresponsive beta-cells.
To assess whether different electrophysiological characteristics could account for the heterogeneous secretion of individual beta-cells in vitro, we used patch-clamp configurations to study currents in plaque-forming (insulin-secreting) and non-plaque-forming rat pancreatic beta-cells that were distinguished in a reverse hemolytic plaque assay (RHPA) after a 30-min stimulation by 16.7 mM glucose. RHPA showed that the population of single beta-cells under study was stimulated (P less than 0.01-0.001) to secrete insulin by 16.7 mM glucose, 100 microM tolbutamide, 20 microM glyburide, or 30 mM KCl but, under these conditions, also comprised beta-cells that did not secrete detectable amounts of insulin. Under current clamp conditions, secreting and nonsecreting beta-cells showed analogous resting membrane potentials (approximately 60 mV) and were similarly depolarized by 30 mm KCl and 100 microM tolbutamide. Under voltage-clamp conditions, total membrane conductance (approximately 6 nS) was also similar in the glucose-responsive and -unresponsive beta-cells, which, when monitored in the whole-cell configuration after RHPA, showed the following currents: a voltage-dependent Na+ current, a voltage-activated Ba2+ current, a voltage-dependent K+ delayed-rectifier current, a voltage-dependent Ca(2+)-activated K+ current, and a voltage-independent and tolbutamide-sensitive K+ current. In the cell-attached configuration and the presence of 2.8 mM glucose, secreting and nonsecreting beta-cells displayed a similar single-channel activity that was abolished when glucose concentration was raised to 16.7 mM. We conclude that beta-cells studied after RHPA have an electrically normal membrane whether they release insulin in response to 16.7 mM glucose or not.
Soria
B
B
Department of Physiology, School of Medicine, University of Alicante, Spain.
Chanson
M
M
Giordano
E
E
Bosco
D
D
Meda
P
P
D000818:Animals; D003035:Cobalt / Q000494:pharmacology; D004594:Electrophysiology / Q000379:methods; D005947:Glucose / Q000494:pharmacology*; D005905:Glyburide / Q000494:pharmacology; D006462:Hemolytic Plaque Technique; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D015222:Sodium Channels / Q000502:physiology; D014044:Tolbutamide / Q000494:pharmacology
D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels; D003035:Cobalt; D011189:Potassium Chloride; D014044:Tolbutamide; C018021:cobaltous chloride; D005947:Glucose; D005905:Glyburide