AN EXTRACELLULAR SIGNALING COMPONENT IN PROPAGATION OF ASTROCYTIC CALCIUM WAVES

Focally evoked calcium waves in astrocyte cultures have been thought t o propagate by gap-junction-mediated intercellular passage of chemical signal(s). In contrast to this mechanism we observed isolated astrocy tes, which had no physical contact with other astrocytes in the cultur e, participating in a calcium wave. This observation requires an extra cellular route of astrocyte signaling. To directly test for extracellu lar signaling we made cell-free lanes 10-300 mu m wide in confluent cu ltures by deleting astrocytes with a glass pipette, After 4-8 hr of re covery, regions of confluent astrocytes separated by lanes devoid of c ells were easily located, Electrical stimulation was used to initiate calcium waves. Waves crossed narrow (<120 mu m) cell-free lanes in 15 of 36 cases, but failed to cross lanes wider than 120 mu m in eight of eight cases, The probability of crossing narrow lanes was not correla ted with the distance from the stimulation site, suggesting that cells along the path of the calcium wave release the extracellular messenge r(s). Calculated velocity across the acellular lanes was not significa ntly different from velocity through regions of confluent astrocytes. Focal superfusion altered both the extent and the direction of calcium waves in confluent regions, These data indicate that extracellular si gnals may play a role in astrocyte-astrocyte communication in situ.