Activation of muscarinic and serotonergic receptors results in phosphoinositide hydrolysis but not in mobilization of calcium in sympathetic neurons.
The effects of various neurotransmitters on phosphoinositide hydrolysis, mobilization of Ca2+ and release of [3H]-norepinephrine ([3H]-NE) were studied in cultures of sympathetic neurons of chick embryos. [3H]-inositol-1,4,5-triphosphate ([3H]-IP3) was increased in sympathetic neurons by acetylcholine (ACh), muscarine and serotonin (5-HT). Dopamine and norepinephrine did not stimulate phosphoinositide hydrolysis. Intracellular concentration of free Ca2+ ([Ca2+]i) was measured in Indo-1-loaded sympathetic neurons at rest and after addition of test agents. Measurements were made in the cell body and growth cone regions since Ca2+ mobilization is known to be different in different regions of the sympathetic neurons. ACh (nicotinic component was blocked by hexamethonium) and 5-HT failed to increase the [Ca2+]i, in the cell body as well as in the growth cone. The spontaneous release of [3H]-NE was not affected by ACh and 5-HT. Caffeine increased the [Ca2+]i only in the cell body but not in the growth cone and had no effect on the release of [3H]-NE. These results suggest that an IP3-insensitive but caffeine-sensitive pool of Ca2+ is present only in the somatic region of sympathetic neurons and is not coupled to the transmitter release.
Wakade
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Department of Pharmacology, Wayne State University, School of Medicine, Detroit, Mich.
Bhave
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Bhave
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Wakade
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D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002642:Chick Embryo; D004298:Dopamine / Q000494:pharmacology; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000378:metabolism; D009116:Muscarine / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000502:physiology*; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000378:metabolism*
D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D011985:Receptors, Serotonin; D012701:Serotonin; D002110:Caffeine; D009116:Muscarine; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D004298:Dopamine; D009638:Norepinephrine