title: Low concentrations of caffeine raise intracellular calcium concentration only in the presence of extracellular calcium in cultured molluscan neurons.
abstract: 1. The effects of low concentrations of caffeine (100 and 300 microM) on the intracellular calcium concentration [Ca2+]i in four cultured, identified neurons of the pond snail Lymnaea stagnalis (L) were investigated. 2. Intracellular CA2+ levels in these neurons were measured with the cell-permeable Ca2+ indicator Fura-2/AM, both in the presence and absence of extracellular Ca2 (o-Ca2+/EGTA). 3. In the presence of Ca2+ in the external medium, caffeine was found to induce a substantial elevation in the free [Ca2+]i in all cell types. 4. In some cases, the rise in [Ca2+]i was found to be both time- and concentration-dependent. 5. Low doses of caffeine did not produce any appreciable rise in [Ca2+]i in the absence of Ca2+ in the external medium, but calcium was still available from stores, as clinical concentrations of halothane rose [Ca2+]i in the absence of extracellular calcium. 6. These results indicate that the actions of caffeine, when applied at low concentrations, are dependent on extracellular calcium.
authors.affiliation: Department of Physiology, University of Leeds, UK.
authors.forename: I A
authors.initials: IA
authors.lastname: Ahmed
authors.forename: P M
authors.initials: PM
authors.lastname: Hopkins
authors.forename: W
authors.initials: W
authors.lastname: Winlow
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002478:Cells, Cultured; D008195:Lymnaea; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002110:Caffeine; D002118:Calcium