Sensitivity to Cd2+ but resistance to Ni2+ of Ca2+ inflow into rat pancreatic islets.
The presence of different types [long lasting (L) and transient (T)] of active voltage-operated Ca2+ channels in islet cells was investigated by comparing the effects of Cd2+, Ni2+, and 1,4-dihydropyridines on 45Ca uptake, 45Ca efflux, and insulin release in intact rat pancreatic islets. In several other excitable cells the L-channel has been shown to be modulated by 1,4-dihydropyridines and Cd2+, whereas the T-channel was reported to be sensitive to Ni2+. Nifedipine and Cd2+ inhibited whereas BAY K 8644 enhanced the glucose (11.1, 22.2 mM)-stimulated short-term 45Ca uptake, 45Ca efflux, and insulin release. In contrast, the stimulatory effects of glucose (11.1, 22.2 mM) on 45Ca uptake, 45Ca efflux, and insulin release were unaffected by Ni2+. These findings confirm that glucose provokes Ca2+ entry mainly by activating voltage-sensitive Ca2+ channels of the L-type and suggest that the B-cell plasma membrane is not equipped with active T-type Ca2+ channels.
Plasman
P O
PO
Laboratory of Pharmacology, Brussels Free University, School of Medicine, Belgium.
Hermann
M
M
Herchuelz
A
A
Lebrun
P
P
D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000502:physiology*; D007700:Kinetics; D009532:Nickel / Q000494:pharmacology*; D051381:Rats
D015220:Calcium Channels; D002104:Cadmium; D009532:Nickel; D005947:Glucose; D002118:Calcium