Thapsigargin-sensitive cationic current leads to membrane depolarization, calcium entry, and insulin secretion in rat pancreatic beta-cells.
Glucose-induced insulin secretion by pancreatic beta-cells depends on membrane depolarization and [Ca2+]i increase. We correlated voltage- and current-clamp recordings, [Ca2+]i measurements, and insulin reverse hemolytic plaque assay to analyze the activity of a thapsigargin-sensitive cationic channel that can be important for membrane depolarization in single rat pancreatic beta-cells. We demonstrate the presence of a thapsigargin-sensitive cationic current, which is mainly carried by Na+. Moreover, in basal glucose concentration (5.6 mM), thapsigargin depolarizes the plasma membrane, producing electrical activity and increasing [Ca2+]i. The latter is prevented by nifedipine, indicating that Ca2+ enters the cell through L-type Ca2+ channels, which are activated by membrane depolarization. Thapsigargin also increased insulin secretion by increasing the percentage of cells secreting insulin and amplifying hormone secretion by individual beta-cells. Nifedipine blocked the increase completely in 5.6 mM glucose and partially in 15.6 mM glucose. We conclude that thapsigargin potentiates a cationic current that depolarizes the cell membrane. This, in turn, increases Ca2+ entry through L-type Ca2+ channels promoting insulin secretion.
Cruz-Cruz
R
R
Department of Biophysics, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Mexico City, Mexico, Mexico.
Salgado
A
A
Sánchez-Soto
C
C
Vaca
L
L
Hiriart
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D019284:Thapsigargin / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002412:Cations; D004791:Enzyme Inhibitors; D007328:Insulin; D019284:Thapsigargin; D009543:Nifedipine; D005947:Glucose; D002118:Calcium