A novel effect of cyclic AMP on capacitative Ca2+ entry in cultured rat cerebellar astrocytes.
One of the most important intracellular Ca2+ regulatory mechanisms in nonexcitable cells, "capacitative Ca2+ entry" (CCE), has not been adequately studied in astrocytes. We therefore investigated whether CCE exists in cultured rat cerebellar astrocytes and studied the roles of cyclic AMP (cAMP) and protein kinase C (PKC) in CCE. We found that (1) at least two different intracellular Ca2+ stores, the endoplasmic reticulum and mitochondria, are present in cerebellar astrocytes; (2) CCE does exist in these cells and can be inhibited by Ni2+, miconazole, and SKF 96365; (3) CCE can be directly enhanced by an increase in intracellular cAMP, as 8-bromoadenosine 3',5'-cyclic monophosphate (8-brcAMP), forskolin, and isobutylmethylxanthine have stimulatory effects on CCE; and (4) neither of the two potent protein kinase A (PKA) inhibitors, H8 and H89, nor a specific PKA agonist, Sp-adenosine 3',5'-cyclic monophosphothioate, had a significant effect on cAMP-enhanced Ca2+ entry. The [Ca2+]i increase was not due to a release from calcium stores, hyperpolarization of the membrane potential, inhibition of calcium extrusion, or a change in pHi, suggesting that cAMP itself probably acts as a novel messenger to modulate CCE. We also conclude that activation of PKC results in an increase in CCE. cAMP and PKC seem to modulate CCE by different pathways.
Wu
M L
ML
Institute of Physiology, College of Medicine, National Taiwan University, Taipei.
Chen
W H
WH
Liu
I H
IH
Tseng
C D
CD
Wang
S M
SM
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism / Q000502:physiology*; D004789:Enzyme Activation; D005260:Female; D006863:Hydrogen-Ion Concentration; D008297:Male; D008564:Membrane Potentials; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
D015220:Calcium Channels; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium