Osmoregulation in the amphibian egg the influence of calcium

Abstract

Determinations of the permeability coefficient for water show that the osmotic behavior of amphibian eggs (ovarian and coelomic eggs from Rana temporaria) cannot be accounted for by this factor alone. Comparison of the cortical stiffness of coelomic eggs with vitelline membrane i n iso-and hypotonic solutions indicate that a mechanical tension develops under hypotonic conditions, strong enough to resist osmotic swelling.In Ca++-free media preservation of this tension is interfered with, but the effect is observed only after exposure for some hours.C a + + does not change the diffusion coefficient for water i n the egg cytoplasm, nor the permeability coefficient for water through the cell membrane. Neither is the Young's modulus for the vitelline membrane influenced. A slight effect of C a + + on the cortical stiffness of naked coelomic eggs was observed. In hypotonic Ca++-free media no resistance to swelling develops in these eggs, and they disintegrate after a rather short time.To determine the permeability to water the rate of DzO -HzO exchange was measured with the Cartesian diver balance. The stiffness was determined with a cell elastimeter described by Mitchison and Swann, and the osmotic swelling was determined by measuring the egg diameter with a n eyepiece screw micrometer.

Mechanosensitivity of the Cardiac Muscarinic Potassium Channel

“…2, a and b). The full decrease took about 10 min to develop, comparable to the time course of osmotic swelling documented in previous studies in oocytes (18) and was reversible over a similar time course upon restoring normal osmolarity (Fig. 2, a and b).…”

ClC-3 Is a Fundamental Molecular Component of Volume-sensitive Outwardly Rectifying Cl− Channels and Volume Regulation in HeLa Cells and Xenopus laevis Oocytes

“…HeLa cells and X. laevis oocytes undergo RVD following cell swelling by hypotonic stress (11,68,69), and VSOACs have been proposed to be an important osmosensitive Cl Ϫ conductance responsible for RVD (11,53). We found that RVD was significantly impaired in HeLa cells acutely transfected with ASO-ClC-3 and X. laevis oocytes injected with antisense when evaluated after 48 h and 72 h, respectively.…”

Hypotonicity activates a native chloride current in Xenopus oocytes.

“…Amphibian oocytes regulate their volume during both hypotonic (Berntsson, Haglund, and Lovtrup, 1965) and hypertonic exposure (Dick and Dick, 1970). Berntsson et al (1965) demonstrated a 20% increase in the volume of ovarian eggs from Rana temporaria within 1 h after exposure to a hypotonic (50% Ringer's) solution; RVD was complete within 24 h. They suggested that RVD was achieved, independent of extracellular calcium, through the generation of mechanical tension in the vitelline membrane (ultrafiltration). Indirect measurements indicated that the intracellular pressure increased 10-fold in these oocytes, from 0.02 mm Hg in 220 mOsm Ringer's solution to 0.2 mm Hg in 50% (110 mOsm) Ringer's solution (Mild, Lovtrup, and Bergfors, 1974).…”