Pituitary adenylate cyclase-activating polypeptide (PACAP) mobilizes intracellular free calcium in cultured rat type-2, but not type-1, astrocytes.
We investigated the effects of pituitary adenylate cyclase-activating polypeptide (PACAP38) on cytosolic free calcium ([Ca2+]i) at a single cell level in both type-1 and type-2 cultured rat astrocytes using a calcium-sensitive fluorescent dye, fura-2. Type-1 astrocytes were relatively silent during the 20 min observation of baseline [Ca2+]i and PACAP38 did not alter [Ca2+]i in type-1 astrocytes at concentrations up to 1 microM. In contrast, type-2 astrocytes could be divided into three subtypes (silent type, randomly-firing type and oscillatory type) based on the observation of baseline [Ca2+]i. Of 166 type-2 astrocytes tested, 145 (87.4%) were the silent type (stable basal [Ca2+]i levels) and 13 (7.8%) were the randomly-firing type (random increases in [Ca2+]i). PACAP38 could stimulate [Ca2+]i in subpopulations of all three subtypes. In the silent type-2 astrocytes (4 experiments with 255 cells/experiment), 54.4 +/- 3.6% of the total number responded to PACAP38. The half maximal concentration (ED50) of PACAP38 was 2.89 +/- 1.89 nM. Removing Ca2+ from the superfusion media did not alter the PACAP38-induced increase of [Ca2+]i. Neither 1-30 microM of forskolin nor 1-10 mM of dibutyryl cyclic AMP increased [Ca2+]i in the same type-2 astrocytes which responded to PACAP38. These findings suggest that PACAP increases [Ca2+]i in type-2, not type-1, rat astrocytes by mobilizing Ca2+ from intracellular stores, and that this action is not linked to activation of the cyclic AMP second messenger system.
US-Japan Biomedical Research Laboratories, Tulane University Hebert Center, Belle Chasse, LA 70037.
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Tatsuno
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Arimura
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002450:Cell Communication / Q000187:drug effects; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D016257:Fura-2; D018698:Glutamic Acid / Q000378:metabolism; D009474:Neurons / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D051381:Rats
C495403:Adcyap1 protein, rat; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D005576:Colforsin; D018698:Glutamic Acid; D003994:Bucladesine; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2