Theoretically predicted effects of Gaussian curvature on lateral diffusion of membrane molecules.

Lateral diffusion on curved biological membranes has been studied theoretically and experimentally. However, how membrane geometries influence the diffusion process remains unclear. Here we show the significance of Gaussian curvature by numerically solving the diffusion equation in a geodesic polar coordinate system with regard to several types of surfaces including elliptic and hyperbolic paraboloids.

Difference in distribution of membrane proteins between low- and high-density secretory granules in parotid acinar cells.

Secretory granules (SGs) are considered to be generated as immature granules and to mature by condensation of their contents. In this study, SGs of parotid gland were separated into low-, medium-, and high-density granule fractions by Percoll-density gradient centrifugation, since it was proposed that the density corresponds to the degree of maturation. The observation with electron microscopy showed that granules in the three fractions were very similar.

A primary culture of parotid acinar cells retaining capacity for agonists-induced amylase secretion and generation of new secretory granules.

Exocrine acinar cells, like parotid cells, have difficulty in maintaining their functions in cell lines or in primary cultures. For this reason, molecular studies on exocrine cell functions are unsatisfactory. To examine the mechanisms whereby the functions of parotid acinar cells are maintained, we attempted to establish a system for primary culture and transfection of exogenous genes.

Phosphodiesterases 1 and 2 regulate cellular cGMP level in rabbit submandibular gland cells.

In rabbit salivary glands, stimulation of muscarinic cholinergic receptors causes production of cGMP through intracellular Ca2+ and nitric oxide. In this study, we investigated a role of cyclic nucleotide phosphodiesterase (PDE) in regulating the cellular cGMP level by using cells dispersed from the submandibular gland. Methacholine, a cholinergic agonist, rapidly elevated the cGMP level.

Theoretical evidence that more microtubules reach the cortex at the pole than at the equator during anaphase in sea urchin eggs.

Astral microtubules are rapidly elongated during anaphase and telophase in sea urchin eggs. The number of microtubules extending to the cell surface was calculated with a computer. For the calculations, microtubules were assumed to radiate from the astral center uniformly over angles.

Why does a cleavage plane develop parallel to the spindle axis in conical sand dollar eggs? A key question for clarifying the mechanism of contractile ring positioning.

Three types of models have been proposed about how the mitotic apparatus determines the position of the cleavage furrow in animal cells. In the first and second types, the contractile ring appears in a cortical region that least and most astral microtubules reach, respectively. The third type is that the spindle midzone positions the contractile ring.

The cleavage plane will bend when one aster of the mitotic apparatus stops growing in compressed sea urchin eggs.

Astral microtubules are elongated greatly during anaphase and telophase in sea urchin eggs. The surface density of microtubules reaching the cell surface can be defined at each surface point. Gradients of the surface-density function were assumed to drive membrane proteins whose accumulation causes the formation of contractile-ring microfilaments.