Aequorin luminescence has been utilized to determine the spatial and temporal fluctuations of the free calcium ion concentration [Ca++] in Chaos carolinensis during ameboid movement, pinocytosis, and capping. The [Ca++] increases above approximately 10(-7) M during normal ameboid movement. Three types of luminescent signals are detected in cells: continuous luminescence, spontaneous pulses, and stimulated pulses. Continuous luminescence is localized in the tails of actively motile cells, and spontaneous pulses occur primarily over the anterior regions of cells. We are sometimes able to correlate the spontaneous pulses with extending pseudopods, whereas stimulated pulses are induced by mechanical damage, electrical stimulation, concanavalin A-induced capping, and pinocytosis. The localization of both distinct actin structures and sites where [Ca++] increases suggests cellular sites of contractile activity. The independent evidence from localizing actin structures and the distribution of [Ca++] can also be viewed in relation to the solation-contraction coupling hypothesis defined in vitro.
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