Alpha-receptor and cholinergic receptor-linked changes in cytosolic Ca2+ and membrane potential in primary rat astrocytes.
Both phenylephrine and carbachol caused a sustained increase in Ca2+ influx and intracellular free Ca2+ of primary astrocytes as measured with 45Ca2+ and fura-2. The responses to phenylephrine and carbachol were additive, suggesting that they use different releasable pools of Ca2+. If extracellular Ca2+ was removed by EGTA only a transient rise in cytosolic Ca2+ was seen upon application of the agonists. Both compounds caused depolarization of the astrocyte membrane as determined with the optical probe 3,3-diethylthiadicarboxyamineiodide. Activation of protein kinase C with 12-tetradecanoylphorbol myristate acetate (TPA) or the diacylglycerol analogue dioctanoylglycerol (DiC8) also depolarized the cells. A prior activation of protein kinase C with TPA or DiC8 abolished the depolarizing effect of phenylephrine suggesting that they act through the same mediators. If the cells were made ideally permeable to K+ with the ionophore valinomycin, or the K+ channels had been blocked with Ba2+, neither TPA nor phenylephrine had any significant effect on the membrane potential. Neither TPA nor phenylephrine had any effect on the 86Rb+ equilibrium potential across the cell membrane. The results suggest that the depolarizing effect of these substances could be through a blocking of K+ channels.
Enkvist
M O
MO
Department of Biochemistry and Pharmacy, Abo Akademi, Turku, Finland.
Holopainen
I
I
Akerman
K E
KE
D000818:Animals; D001253:Astrocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D008564:Membrane Potentials / Q000187:drug effects; D010656:Phenylephrine / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism* / Q000502:physiology; D011950:Receptors, Cholinergic / Q000378:metabolism* / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D015221:Potassium Channels; D011942:Receptors, Adrenergic, alpha; D011950:Receptors, Cholinergic; D010656:Phenylephrine; D014634:Valinomycin; D002217:Carbachol; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium