AXONAL ACTIVATION-INDUCED CALCIUM TRANSIENTS IN MYELINATING SCHWANN-CELLS, SOURCES, AND MECHANISMS

We have investigated the role of myelinating glia in events associated with propagation of the action potential at nodes of Ranvier using co mbinations of optical and electrophysiological recording methods, Calc ium transients were observed in Schwann cells by fluorescent imaging o f the nodal complex of fibers loaded with the calcium-sensitive dye fl uo3-AM. To follow [Ca2+](i) changes associated with neuronal activity at the node of Ranvier, nerves loaded with fluo3 were imaged during ax onal activation using laser-scanning confocal microscopy. To elucidate sources of [Ca2+](i) transients, we tested the effects of drugs known to alter [Ca2+](i). [Ca2+](i) transients in Schwann cells were observ ed in response to axonal activation and these were subsequently blocke d by ryanodine if ryanodine was present during a previous [Ca2+](i) tr ansient. Bath applications of caffeine induced [Ca2+](i) transients wh ich could be blocked by ryanodine, These findings indicate that calciu m-activated calcium release occurs in Schwann cells in response to imp ulse activity.