Glucose, potassium, and CCK-8 induce increases in membrane-associated PKC activity that correspond to increases in [Ca2+]i in islet cells from neonatal rats.
The effects of glucose, K+, and cholecystokinin octapeptide (CCK-8) on intracellular free Ca2+ concentration ([Ca2+]i) and membrane-associated protein kinase C (PKC) activity were examined in cultured islet cells from neonatal rats. Raising the glucose concentration from 2.8 to 22.2 mM or external K+ (from 5 to 45 mM), or adding CCK-8 (200 nM) all triggered a [Ca2+]i surge that peaked between 3 and 10 min afterward, depending on the stimulus, and then declined, either to a suprabasal plateau (glucose and K+) or to basal levels (CCK-8). These same manipulations triggered a burst of membrane-associated PKC activity that peaked between 5 and 10 min and then variously declined. Incubation in Ca(2+)-free medium abolished both the effects of glucose and K+ on [Ca2+]i and the stimulation of membrane-associated PKC activity. The K(+)-triggered stimulation of PKC activity was also inhibited by pretreating the cells with the general Ca2+ entry blocker lanthanum (1 mM). However, incubation in Ca(2+)-free medium did not affect the CCK-8-induced release Ca2+ from internal stores, although it abolished the burst of membrane-associated PKC activity, which showed the importance of Ca2+ influx as opposed to internal release for PKC activation. Thus, glucose, the principal stimulator of insulin secretion, rapidly stimulates Ca2+ influx into islet cells from neonatal rats, and it is probably this influx that stimulates membrane-associated PKC activity.
Wang
J
J
Department of Biochemistry, University of Ottawa, Ontario, Canada.
Chakravarthy
B R
BR
Morley
P
P
Whitfield
J F
JF
Durkin
J P
JP
Bégin-Heick
N
N
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D005260:Female; D005947:Glucose / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D011188:Potassium / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012844:Sincalide / Q000494:pharmacology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007811:Lanthanum; D011493:Protein Kinase C; D005947:Glucose; D012844:Sincalide; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium