The melanocytes of isolated fish scales (Fundulus heteroclitus) immersed in 0.1 M aqueous KCI solution and in deuterated KC1 solutions, in which 50-70% of the H2O was replaced by DTO, were observed at 300X magnification while they were subjected to increasing hydrostatic pressure, raised in increments of 1,000 psi in the range up to 16,000 psi. In one series of experiments the temperature was maintained at 20Β°C (2 0.2'), whereas in the other it was kept a t 25Β°C (2 0.2).
Initially, all the melanocytes in the KC1 media displayed a contracted, or punctate, form. With increasing pressures, gradually, expansion, or pigment granule dispersal, occurred but the degree of expansion at a given pressure depended upon the percentage of deuteration and the temperature. At 20Β°C in aqueous medium, total expansion, in which the pigment extended all the way out into the peripheral tips of melanocyte branches, occurred at 8,000-9,000 psi. At lower pressure, the intermediate values, expressed as a percentage of the total, fell along a smooth, slightly sigmoid curve. In the deuterated media, similar curves were obtained, but the pressure levels required to produce a given degree of expansion were significantly higher. Thus, maximum expansion required the imposition of 14,000 psi in the 50% D2O medium and of 16,000 psi in the 70%. Upon decompression, at the end of each experiment, the melanocytes quickly contracted, reaching a completely punctate form within 3-4 minutes.
Similar relationships were found at 25"C, except that all the pressure values were significantly higher than those at 20Β°C. In fact the values for 25", with 50% deuteration, were very similar to those for 20", with 70% DzO.
The evidence tends to confirm conclusions, previously submitted, namely, that, as expansion occurs, the cytoplasm of the unicellular pigmentary effectors of the fish undergoes a progressive process of solation and that contraction involves a reestablishment of the original firm gel structure. Thus the well known solational effects of high pressure tend to be counteracted bv agencies. such as increasincl deuteration and' temperature, which are generally.