Ionic analyses and effects of ions on contractions of sponge tissues

Summary

Contractions of oscular membranes of several marine sponges in response to mechanical stimuli were recorded in various ionic media. Previously, failure to record action potentials and to stimulate electrically was reported.

Contractions persisted when sodium was replaced by lithium or potassium but not when the replacement was by choline or sucrose. Contractions were maintained in sea water in which the only univalent cation was potassium; they also persisted in Na-sea water without potassium.

Contractions stopped when either calcium or magnesium was omitted, but addition of an equivalent extra amount of the other divalent cation then restored contractions. Contractions were also maintained when strontium was substituted for calcium and magnesium.

Analyses of contractile membranes yielded average values for Naples sponges of Na 375 mM/kg H₂O, K 29.8 mM/kg H₂O and inulin space 48.9% of H₂O; for Woods Hole Microciona in mM/kg H₂O: Na 300, K 66, Ca 8.4, Cl 225, inulin space 40% H₂O. The calculated intracellular concentrations for Microciona in mM/kg H₂O were: Na 216, K 104.5, Ca 7.8, Cl 45 yielding i/o ratios of Na 0.5, K 11.6, Ca 0.84, Cl 0.09.

It is concluded that, despite relatively normal ionic ratios, mechanical stimuli activate the contractile system in sponges more directly than in muscle.