Osmotic Relations in Molluscan Contractile Tissues

Abstract

1. An investigation was made into the effects of variations of osmotic pressure of the bathing fluid on isolated ventricle preparations from three species of lamellibranchs. 2. Suitable media were found in sea water for Mytilus and Ostrea and 4% sea water for Anodonta. Under the conditions described, a regular beat resembling the natural beat is maintained for days, although the media used differ somewhat in ionic composition from the natural body fluids. 3. Sudden changes in concentration of the bathing media lead to temporary ‘Shock reactions’ followed by accommodation. The shock effects can be avoided by gradual changes in concentration, the final effects being essentially the same whether the change is gradual or abrupt. 4. In all species, the shock reaction included reduction in amplitude or even inhibition of the rhythm, and also the following effects, which depend on the direction of change of concentration. Change from a normal to a hypotonic medium, or return from a hypertonic to a normal medium, caused tone rise or systolic contracture; change from a normal to a hypertonic medium, or return from a hypotonic to a normal medium, caused tone lowering or diastolic relaxation. 5. The beat after the shock reactions had passed off was in general faster in hypertonic and slower in hypotonic media. In the marine species, however, there was also slowing in the most concentrated media capable of supporting a beat. 6. A comparison is drawn between features of the activity and metabolism of the three species and the concentration of their bloods. It is suggested that the very dilute blood of the fresh-water mussel restricts its heart rate, general activity and metabolism. 7. The tissues investigated are shown to tolerate ranges in the concentration of media wider than those encountered under natural conditions, and it is suggested that salinity of the environment is not a critical factor in restricting the ecological distribution of adults of the species. The tolerance of the tissues may have a safe guarding effect in the event of temporary inefficiency in the osmoregulatory mechanism.