Spatial heterogeneity of caffeine- and inositol 1,4,5-trisphosphate-induced Ca2+ transients in isolated snail neurons.
Inositol 1,4,5-trisphosphate- and caffeine-induced Ca2+ release was examined in neurons isolated from the mollusc Helix pomatia using Ca2+ indicator fura-2 and fluorescent digital-imaging microscopy technique. Extracellular application of caffeine caused a fast and pronounced augmentation of [Ca2+]i whose amplitude and kinetics differ in the centre of the cell and near its membrane. Mean values of caffeine-induced increase of [Ca2+]i were 0.97 +/- 0.11 microM at the periphery and 0.53 +/- 0.13 microM in the centre. The rates of rise and relaxation of caffeine-evoked [Ca2+]i transients were faster near the membrane. Pressure injection of inositol, 1,4,5-trisphosphate into the same neurons produced an abrupt and significant increase of [Ca2+]i in the centre (mean value of inositol 1,4,5-trisphosphate-induced elevation = 0.55 +/- 0.11 microM) while the response was smaller or even absent near the cellular membrane. Inositol 1,4,5-trisphosphate- and caffeine-induced Ca2+ transients did not affect each other. The data obtained indicate that in snail neurons these two calcium pools are not overlapping and at least some part of the caffeine-sensitive store is located close to the cellular membrane and that the inositol 1,4,5-trisphosphate-sensitive one is located in the centre of the cell.
Bogomoletz Institute of Physiology, Kiev, Ukraine.
P G
PG
Kostyuk
S I
SI
Kirischuk
D000818:Animals; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D016257:Fura-2; D006372:Helix, Snails / Q000378:metabolism*; D066298:In Vitro Techniques; D007293:Inosine Triphosphate / Q000494:pharmacology*; D008564:Membrane Potentials / Q000502:physiology; D008839:Microelectrodes; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D012433:Ryanodine / Q000494:pharmacology
D007293:Inosine Triphosphate; D012433:Ryanodine; D002110:Caffeine; D002118:Calcium; D016257:Fura-2