REGULATION OF MOTILITY OF CELLS FROM MARINE SPONGES BY CALCIUM-IONS

Sponges are known not to contain muscle and nerve cells. Since sponge cells are characterized by high motility we determined the effect of i ntracellular calcium ion concentration ([Ca2+](i)) on their motility. Addition of the Ca2+ ionophore ionomycin to dissociated cells from the marine sponge Suberites domuncula caused in Ca2+-containing artificia l seawater (ASW) an increase in motility from 0.2 mu m/min (absence of the ionophore) to 3.7 mu m/min (presence of ionomycin). When the expe riments were performed in Ca2+-free medium, no effect of ionomycin cou ld be observed. In parallel experiments the changes of [Ca2+](i) using the dye Fura-2 were measured. The experiments revealed that ionomycin causes an influx of Ca2+ into the cytosol of cells suspended in Ca2+- containing artificial seawater. In contrast, if cells were suspended i n Ca2+-free artificial seawater, no increase of [Ca2+](i) occurred. In cubation of cells in the presence of inhibitors, specific for endoplas matic Ca2+-ATPase in mammals such as thapsigargin, cyclopiazonic acid, or 2,5 di-t-butylhydrochinone, did not influence the [Ca2+](i) if cel ls were suspended in Ca2+-free artificial seawater. From these data we conclude that the [Ca2+](i) is primarily regulated through channels i n the plasma membrane. In addition we summarize experimental evidence indicating that the [Ca2+](i) is involved in the control of cell motil ity. From the marine sponge Geodia cydonium a partial sequence of the myosin cDNA has been cloned. The deduced amino acid sequence comprises highest homology to nonmuscle myosin type II found in higher inverteb rates and vertebrates. Taken together, these data show that the [Ca2+] (i) level in sponge cells can be modulated by incubation with ionomyci n. An increase of the Ca2+ level parallels with higher motility of cel ls, suggesting an activation of Ca2+-dependent protein kinases of myos in type II. Investigations on the ionomycin-activated influx of Ca2+ i nto the cytosol revealed that predominantly the Ca2+ channels in plasm a membrane control the level of [Ca2+] (i). Copyright (C) 1996 Elsevie r Science Inc.