Electrical control of flagellar activity in impaled bull spermatozoa

1979 ◽  
Vol 35 (1) ◽  
pp. 123-138
Author(s):  
P.M. O'Day ◽  
R. Rikmenspoel
Keyword(s):  
Cell Membrane ◽  
Direct Current ◽  
Transport Process ◽  
Current Injection ◽  
Magnesium Concentration ◽  
Electrical Control ◽  
Transmembrane Potentials ◽  
Negative Current ◽  
Bull Spermatozoon ◽  
Active Transport Process

The control of bull spermatozoon flagellar activity has been investigated using direct current injection into the cells through an impaling glass microelectrode. Negative current injection results in a decrease in the flagellar frequency. Flagellar frequencies can be decreased to zero with high negative currents. This current injection response is dependent on the magnesium concentration available to the spermatozoon interior. The current injection response is nearly independent of ATP concentrations. Resistance measurements indicate that the current injection pathway has a resistance of about 200 +/− 300 k omega, and that the current flowing through the cell membrane is not exceedingly large. Measurements of the induced potentials indicate transmembrane potentials during current injection of about −35 +/− 30 mV per microA of injected current. The results are compatible with an active transport process in bull spermatozoa that controls the flagellar activity in response to current injection by decreasing the internal Mg2+ concentrations during the injection of current.

scholarly journals The Influence of the Intracellular Potential on Potassium Uptake by Beetroot Tissue

1966 ◽  
Vol 49 (3) ◽  
pp. 551-563 ◽  
Author(s):  
Ronald J. Poole
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Metabolic Activity ◽  
Transport Process ◽  
Equilibrium Potential ◽  
Bicarbonate Concentration ◽  
K Uptake ◽  
Active Transport Process ◽  
Metabolic Transport

Intracellular potentials were measured in beetroot tissue during the steady-state uptake of K+ from various solutions. In solutions containing bicarbonate, the membrane potential becomes up to 70 mv more negative than the estimated equilibrium potential for K+. The uptake of K+ from such solutions is correlated with variations in the potential, both when the bicarbonate concentration is changed and also when the metabolic activity of the tissue is changed by washing in water for various periods. However, the estimated permeability to K+ varies from 0.4 x 10-7 to 1.5 x 10-7 cm·sec-1. It is postulated that the change of potential arises from the metabolic transport of HCO3- into the cell or H+ outwards, and that the associated uptake of K+ is partly or entirely by passive diffusion across the cell membrane. In contrast, K+ uptake from KCl solutions is not accompanied by any significant change in the membrane potential, which remains relatively close to the K+ equilibrium potential. In solutions containing both KHCO3 and KCl, it appears that an amount of K+ equal to the influx of Cl- is taken up independently of the potential, while the component of K+ uptake which is not balanced by Cl- uptake is related to the potential in the manner described. These results suggest that K+ uptake is linked to Cl- uptake in an electrically neutral active transport process.

Mg2+-dependent electrical control of flagellar activity in Euglena

1977 ◽  
Vol 23 (1) ◽  
pp. 211-225
Author(s):  
K.M. Nichols ◽  
R. Rikmenspoel
Keyword(s):  
High Speed ◽  
External Medium ◽  
Average Frequency ◽  
Current Injection ◽  
Initial Activity ◽  
Free Medium ◽  
Electrical Control ◽  
Negative Current ◽  
Smooth Dependence ◽  
Injection Cycle

When a Euglena gracilis in a Ca2+-containing medium is impaled with a microelectrode, the flagellum is instantly ejected. In a Ca2+-free medium to which 1 mM EGTA has been added, the flagellum remains attached to the organism, but it loses activity upon impalement. Externally added ATP at a concentration of 10 mM will sustain normal flagellar activity (at approximately 20 Hz) of an impaled Euglena. If negative direct current of several tenths of a microamp is injected through the impaling microelectrode, the flagellar activity is stopped or much reduced. When the current injection is turned off the flagellum returns to its initial activity. This cycle can be repeated many times on the same animal, independent of whether Mg2+ is present in the external medium or not. If 1 micrometer of gramicidin is added to Ca2+-free medium containing 1 mM EGTA and 10 mM ATP, the flagellar activity becomes dependent on external Mg2+. Without external Mg2+ no flagellar activity is present after one or two current injection cycles as described above. With 1 mM Mg2+ present in the external medium many cycles (up to 10) can be produced. This Mg2+-dependent flagellar activity shows a smooth dependence on the amount of current injected. Observations taken by high speed cinemicrography show that in the third injection cycle the average frequency of the flagellar motion is 16-3 Hz at 0 muA, is 8 Hz at 0-2 muA, and is approximately 0 at 0-6 muA of negative current. The injection of positive current results in an increase in flagellar frequency dependent on the amount of current injected. The data indicate that the control of motility of Euglena flagella is dependent on an electrically activated Mg2+ pump.

A nuclear localization signal can enhance both the nuclear transport and expression of 1 kb DNA

1999 ◽  
Vol 112 (12) ◽  
pp. 2033-2041
Author(s):  
J.J. Ludtke ◽  
G. Zhang ◽  
M.G. Sebestyen ◽  
J.A. Wolff
Keyword(s):  
Active Transport ◽  
Nuclear Localization ◽  
Transport Process ◽  
Nuclear Transport ◽  
Passive Diffusion ◽  
Viral Gene ◽  
Nuclear Localization Signals ◽  
Size Limit ◽  
Cytosolic Extract ◽  
Active Transport Process

Although the entry of DNA into the nucleus is a crucial step of non-viral gene delivery, fundamental features of this transport process have remained unexplored. This study analyzed the effect of linear double stranded DNA size on its passive diffusion, its active transport and its NLS-assisted transport. The size limit for passive diffusion was found to be between 200 and 310 bp. DNA of 310–1500 bp entered the nuclei of digitonin treated cells in the absence of cytosolic extract by an active transport process. Both the size limit and the intensity of DNA nuclear transport could be increased by the attachment of strong nuclear localization signals. Conjugation of a 900 bp expression cassette to nuclear localization signals increased both its nuclear entry and expression in microinjected, living cells.

Creatinine, potassium, and calcium flux from chicken cerebrospinal fluid

1975 ◽  
Vol 228 (2) ◽  
pp. 415-419 ◽  
Author(s):  
DK Anderson ◽  
SR Heisey
Keyword(s):  
Cerebrospinal Fluid ◽  
Transport Process ◽  
Calcium Flux ◽  
Brain Blood Flow ◽  
Artificial Cerebrospinal Fluid ◽  
Bulk Absorption ◽  
Perfusion Time ◽  
Active Transport Process ◽  
Tracer Molecules ◽  
Lateral Cerebral Ventricle

Brains of methoxyflurane-anesthetized chickens were perfused from a lateral cerebral ventricle to cisterna magna with an artificial cerebrospinal fluid (CSF) containing trace quantities of radioiodinated human serum albumin (RIHSA) or inulin (1.0 mg/ml) to measure CSF bulk absorption. In addition, it contained either trace quantities of 22Na, 42K, 45Ca or [14C]creatinine; the concentrations of the latter three were varied to determine permeability coefficients (K-D's) as a function of concentration. A mass balance for the tracer molecules was calculated to determine their movement into brain or blood. K-D's for 45Ca, 42K, 22Na, and creatinine (Cr) were unaffected by perfusion time and the latter two were larger than previously reported (3). The lack of effect of time on K-D and the large values for K-D22Na and K-D-Cr are attributed to anesthetic effects on brain blood flow. K-D-Cr and K-D42K were larger than K-D22Na or K-D45Ca and K-D's for 45Ca, Cr, and 42K were independent of their inflow concentrations. An active transport process is suggested for potassium and creatinine, but one that is located at sites other than the ependymal wall. Bulk flow clearance accounted for RIHSA movement from CSF, whereas nonbulk clearance accounted for 50% of 22Na and 45Ca movement and 90% of 42K clearance. Fifty percent of 42K and 25% of 22Na and 45Ca were found in brain. The large recovery of 42K in brain supports the hypothesis that intracellular potassium serves as an exchangeable pool for the tracer.

Total contents and net movements of magnesium in the rat uterus

1971 ◽  
Vol 220 (6) ◽  
pp. 2067-2067
Author(s):  
A. H. Moawad ◽  
E. E. Daniel
Keyword(s):  
Membrane Potential ◽  
Active Transport ◽  
Extracellular Space ◽  
Transport Process ◽  
Electrochemical Gradient ◽  
Rat Uterus ◽  
Active Transport Process

Page 75: A. H. Moawad and E. E. Daniel. "Total contents and net movements of magnesium in the rat uterus." Page 80, column 2, line 44, involving the calculation of Vm the answer to the equation, –0.067 V, should read, "–0.012 V." Page 80, column 2, lines 49–54 should read, "The calculated magnesium equilibrum potential is less than the observed membrane potential, which is about 0.050 V. Therefore, some of the tissue magnesium may be excluded by an active transport process against an electrochemical gradient or by loose binding in the extracellular space."

Ionic regulation of Na absorption in proximal colon: cation inhibition of electroneutral Na absorption

1987 ◽  
Vol 252 (1) ◽  
pp. G100-G108
Author(s):  
J. H. Sellin ◽  
R. De Soignie
Keyword(s):  
Linear Function ◽  
Active Transport ◽  
Transport Process ◽  
Proximal Colon ◽  
High Rate ◽  
Ionic Regulation ◽  
Diffusional Flux ◽  
Active Transport Process

Active Na absorption (JNanet) in rabbit proximal colon in vitro is paradoxically stimulated as [Na] in the bathing media is lowered with constant osmolarity. At 140 mM [Na]o, JNanet is -0.6 +/- 0.4 mueq X cm-2 X h-1, whereas at 50 mM [Na]o JNanet is 5.0 +/- 0.7 mueq X cm-2 X h-1, P less than 0.01. JNas----m is a linear function of [Na]o, suggesting a diffusional flux. JNam----s increases almost linearly from 0 to 50 mM [Na]o but then plateaus and actually decreases from 50 to 140 mM [Na]o, consistent with inhibition of an active transport process. Both lithium and Na are equally effective inhibitors of JNanet, whereas choline and mannitol do not block the high rate of JNanet observed in decreased [Na]o. Either gluconate or proprionate replacement of Cl inhibits JNanet. Removal of K or HCO3 does not alter Na absorption. JNanet at lowered [Na]o is electrically silent and is accompanied by increased Cl absorption; it is inhibited by 10(-3) M amiloride and 10(-3) M theophylline but not by 10(-4) M bumetanide. Epinephrine is equally effective at stimulating Na absorption at 50 and 140 mM [Na]; yohimbine does not inhibit JNanet at 50 mM [Na]o. Na gradient experiments are consistent with a predominantly serosal effect of the decreased [Na]o. These results suggest that Na absorption in rabbit proximal colon in vitro is stimulated by decreased [Na]; the effect is cation specific, both Na and Li blocking the stimulatory effect.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals A Dual Role for Actin and Microtubule Cytoskeleton in the Transport of Golgi Units from the Nurse Cells to the Oocyte Across Ring Canals

2009 ◽  
Vol 20 (1) ◽  
pp. 556-568 ◽  
Author(s):  
Emmanuelle Nicolas ◽  
Nicolas Chenouard ◽  
Jean-Christophe Olivo-Marin ◽  
Antoine Guichet
Keyword(s):  
Embryonic Development ◽  
Transport Process ◽  
Myosin Ii ◽  
Nurse Cells ◽  
Transport Mechanisms ◽  
Step Process ◽  
Actin Networks ◽  
Ring Canals ◽  
Cytoplasmic Bridges ◽  
Active Transport Process

Axis specification during Drosophila embryonic development requires transfer of maternal components during oogenesis from nurse cells (NCs) into the oocyte through cytoplasmic bridges. We found that the asymmetrical distribution of Golgi, between nurse cells and the oocyte, is sustained by an active transport process. We have characterized actin basket structures that asymmetrically cap the NC side of Ring canals (RCs) connecting the oocyte. Our results suggest that these actin baskets structurally support transport mechanisms of RC transit. In addition, our tracking analysis indicates that Golgi are actively transported to the oocyte rather than diffusing. We observed that RC transit is microtubule-based and mediated at least by dynein. Finally, we show that actin networks may be involved in RC crossing through a myosin II step process, as well as in dispatching Golgi units inside the oocyte subcompartments.

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