Na channels and two types of Ca channels in rat pancreatic B cells identified with the reverse hemolytic plaque assay.
The reverse hemolytic plaque assay (RHPA) was used to study the secretory properties of single rat pancreatic B cells, and to identify insulin-secreting cells for patch-clamp experiments. In secretion studies using the RHPA, we find that the percentage of secreting B cells and the amount of insulin secreted per B cell increase as the glucose concentration is raised from 0 to 20 mM. Using the whole-cell variation of the patch-clamp technique, we find that identified B cells have three types of channels capable of carrying inward current: (a) tetrodotoxin-sensitive, voltage-dependent Na channels, which are nearly completely inactivated at -40 mV, (b) fast deactivating (FD) Ca channels, and (c) slowly deactivating (SD) Ca channels. We have shown that Na channels are functionally significant to the B cell, because tetrodotoxin partially inhibits glucose-induced insulin secretion. The properties of FD and SD Ca channels differ in several respects. FD channels deactivate at -80 mV, with a time constant of 129 microseconds, they are half-maximally activated near +15 mV, they do not inactivate during 100 ms, they conduct Ba2+ better than Ca2+, and they are very sensitive to washout during intracellular dialysis. SD channels, on the other hand, deactivate with a time constant of 2.8 ms, they are half-maximally activated near -5 mV, they inactivate rapidly, they conduct Ba2+ and Ca2+ equally well, and they are insensitive to washout.
Hiriart
M
M
Department of Biophysics, University of Maryland School of Medicine, Baltimore 21201.
Matteson
D R
DR
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005947:Glucose / Q000378:metabolism; D006462:Hemolytic Plaque Technique; D007328:Insulin / Q000032:analysis / Q000276:immunology / Q000378:metabolism*; D000078790:Insulin Secretion; D007473:Ion Channels / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*
D007328:Insulin; D007473:Ion Channels; D012964:Sodium; D005947:Glucose; D002118:Calcium