Comparisons of different stages of chick embryonic development by the physiological regulatory response to hyposmotic challenge

A spring-matrix model for pigment translocation in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi (Crustacea, Decapoda)

A model for intracellular transport of pigment granules in the red ovarian chromatophores of the freshwater shrimp Macrobrachium olfersi is proposed on the basis of shifts in the equilibrium of resting forces acting on an elastic pigment matrix. The model describes a pigment-transport mechanism in which mechanochemical protein motors like kinesin and myosin alternately stretch and compress a structurally unified, elastic pigment matrix. Quantifiable properties of the spring-matrix obey Hooke's Law during the rapid phases of pigment aggregation and dispersion. The spring-like response of the pigment mass is estimated from previous kinetic experiments on pigment translocation induced by red pigment concentrating hormone, or by the calcium ionophore A23187. Both translocation effectors trigger an initial phase of rapid pigment aggregation, and their removal or washout after complete aggregation produces a phase of rapid pigment dispersion, followed by slow pigment translocation. The rapid-phase kinetics of pigment transport are in reasonable agreement with Hooke's Law, suggesting that such phases represent the release of kinetic energy, probably produced by the mechanochemical protein motors and stored in the form of matrix deformation during the slow phases of translocation. This semiquantitative model should aid in analyzing intracellular transport systems that incorporate an elastic component.

A moderate decrease in temperature inhibits the calcium signaling mechanism(s) of the regulatory volume decrease in chick embryo cardiomyocytes

Chick cardiomyocytes, when submitted to hyposmotic swelling, exhibit a partial regulatory volume decrease (RVD). A Ca2+ influx by stretch-activated channels signals a taurine efflux and the RVD at 37 degrees C. We evaluated the cell's performance at room temperature. Cardiomyocytes isolated and cultured from 11-day-old chick embryos were submitted to a hyposmotic solution (180 mOsm/kg H2O) at 37 degrees C and at room temperature (26 degrees C). Under these conditions we measured the changes in cell volume as well as the intracellular free Ca2+ (using fura-2). During hyposmotic swelling, cells at 37 degrees C displayed a peak relative volume of 1.61 +/- 0.03 and recovery to 1.22 +/- 0.04 (N = 14), while cells at 26 degrees C presented a peak swell relative volume of 1.74 +/- 0.06 and did not recover (1.59 +/- 0.09, N = 9). Transient increases in intracellular Ca2+, which are characteristic of the normal RVD, were observed at both temperatures (29.1 +/- 4.5% (N = 8) and 115.2 +/- 42.8% (N = 5) increase at 37 degrees and 26 degrees C (P<0.05), respectively). A delay in the Ca2+ transient increase was also observed when the cells were at 26 degrees C (109 +/- 34 s compared to 38 +/- 9 s at 37 degrees C, P<0.05). At room temperature the RVD does not occur because the calcium transient increase, which is an early event in the signaling of the RVD, is delayed. Also, free calcium is not cleared as in the 37 degrees C RVD. In the normal RVD the free calcium returns to baseline levels. The very high and persistent free calcium levels seen at room temperature can lead to unregulated enzyme activities and may promote irreversible injury and cell death.

Volume changes in cardiac ventricles from Aplysia brasiliana upon exposure to hyposmotic shock

We investigated the possible role of ion channels and transporters in cell volume control using Aplysia brasiliana ventricular tissues exposed to a 26% hyposmotic shock, by assessing changes in wet weight, intracellular water and ionic contents. Thirty minutes after the shock, the wet weight of isolated ventricles increase about 20% above control levels and then attain near original weight within 60 min after the shock. At the time when the wet weight returned to control values, intracellular water and KCl contents are decreased by 22 and 20%, respectively. The K(+) channel blockers, 4-AP and TEA, but not the cotransport blockers, hydrochlorothiazide and furosemide, greatly affect the magnitude of wet weight gain and the time course of weight recovery, indicating that KCl loss occur through conductive pathways. Intracellular recordings performed on ventricular myocytes during exposure to the osmotic shock showed an immediate membrane hyperpolarization and blockade of spontaneous electrical activity; diastolic membrane potential recover over time and spontaneous action potentials are completely restored 60 min after the hyposmotic shock. Because significant weight loss is observed during the exposure of ventricular tissues to 26% hypo-ionic, but isosmotic saline, it is suggested that ventricular volume restoration is accomplished by two distinct but simultaneously occurring processes: a volume-dependent and a volume-independent mechanism. Because wet weight restoration is completely prevented by exposing ventricular tissue to a Ca(2+)-free hyposmotic solution, we postulate that both processes involved in A. brasiliana ventricular weight restoration are Ca(2+)-dependent mechanisms.