Studies on the size, location and turnover of calcium pools accessible to growing Tetrahymena cells

Calcium regulates the regeneration of cilia in Tetrahymena thermophila

A study of calcium metabolism in Tetrahymena during the regeneration of cilia evidenced that the process is inhibited by nifedipine and trifluoperazine. This suggests that calcium ions play an important regulatory role in this process. This was confirmed by studies on calcium uptake and efflux which showed that there was a net increase in calcium uptake prior to the reinitiation of motility. The increase coincided with a period of sensitivity to the calcium antagonist TMB-8 and with an increase in the intracellular level of cGMP. The process was also inhibited by neomycin and stimulated by phorbol esters, which suggests that hydrolysis of phosphatidylinositol phosphates may take place as part of the calcium regulatory network during the regeneration of cilia.

Alterations of the composition and size of the free fatty acid pool of Tetrahymena responding to low-temperature stress

Cells of Tetrahymena mimbres (formerly T. pyriformis NT-1) in midlogarithmic growth under isothermal conditions (at 39 degrees C) contained a very small, compositionally discrete pool of free fatty acids, principally (60.6% of the total free fatty acid mass) palmitic and stearic acids. The composition, degree of unsaturation, and size of this free fatty acid pool were rapidly (15 min or less) altered in response to chilling. During the acclimation period following chilling to 15 degrees C, the size of the free fatty acid pool increased from a mean value of 15.5 nmol free fatty acid/mumol lipid phosphorus in 39 degrees C cells to 24.2 nmol free fatty acid/mumol lipid phosphorus. The degree of free fatty acid saturation rapidly increased over the initial hour following the onset of hypothermal conditions, but by 24 h the unsaturated free fatty acid/saturated free fatty acid ratio was 0.35 (equivalent to a 2.7-fold increase in unsaturation relative to 39 degrees C controls (unsaturated/saturated ratio = 0.13) and 4.4-fold greater than cells acclimated for 1 h (unsaturated/saturated ratio = 0.08)). By 24 h the percentage of palmitic and stearic acids had decreased to 45.6%. Similar, and in some instances more pronounced, changes were observed to occur in triacylglycerol-bound fatty acids. Modulation of steady-state free fatty acid composition could also be achieved by the addition of exogenous fatty acids to the growth medium. The ability to manipulate the level of intracellular free fatty acids should prove to be a valuable experimental tool in determining how specific fatty acids regulate various lipid-modifying enzymes.

Thermal diminution and augmentation of the retention of transportable rRNA in nuclear envelope-free nuclei

We have examined the effect of temperature on the rRNA transport from nuclei isolated from Tetrahymena after removal of both nuclear membranes and pore complexes by 1% Triton X-100. These nuclei export rRNA as precursor ribosomal ribonucleoprotein particles at both 28 degrees C and 8 degrees C which are qualitatively the same in terms of rRNA pattern, sedimentation coefficients and buoyant densities. At 8 degrees C, however, significantly fewer ribosomal ribonucleoprotein particles can be maximally exported than at 28 degrees C, though nuclei contain enough potentially transportable particles. These are increasingly released with increasing temperatures. Under conditions non-permissive for export, temperature elevation decreases the number of the potentially transportable ribosomal ribonucleoprotein particles in nuclei. Our data show: transportable ribosomal ribonucleoprotein particles inside nuclei are not 'free', but rather are subject to a complex temperature-sensitive retention: this retention is gradually diminished under export conditions and augmented under non-permissive export conditions with increasing temperatures. These retention mechanisms operate at an intranuclear level preceding the ribosomal ribonucleoprotein passage through the nuclear envelope pore complexes, i.e., the nuclear envelope regulates neither the number of potentially transportable ribosomal ribonucleoprotein particles in nuclei nor the number of those particles which can be maximally exported from nuclei at a given temperature. We suggest that these retention mechanisms involve temperature-sensitive domains of the nuclear matrix.