scholarly journals Anomalous permeabilities of the egg cell membrane of a starfish in K+-Tl+ mixtures.

1977 ◽  
Vol 70 (3) ◽  
pp. 269-281 ◽  
Author(s):  
S Hagiwara ◽  
S Miyazaki ◽  
S Krasne ◽  
S Ciani
Keyword(s):  
Cell Membrane ◽  
Egg Cell

scholarly journals Two components of the calcium current in the egg cell membrane of the tunicate.

1976 ◽  
Vol 255 (2) ◽  
pp. 527-561 ◽  
Author(s):  
H Okamoto ◽  
K Takahashi ◽  
M Yoshii
Keyword(s):  
Cell Membrane ◽  
Calcium Current ◽  
Egg Cell

scholarly journals Potassium current and the effect of cesium on this current during anomalous rectification of the egg cell membrane of a starfish.

1976 ◽  
Vol 67 (6) ◽  
pp. 621-638 ◽  
Author(s):  
S Hagiwara ◽  
S Miyazaki ◽  
N P Rosenthal
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
K Channel ◽  
Egg Cell ◽  
Dimensionless Number ◽  
First Order Kinetics ◽  
K Current ◽  
Kinetics Of

The kinetics of the membrane current during the anomalous or inward-going rectification of the K current in the egg cell membrane of the starfish Mediaster aequalis were analyzed by voltage clamp. The rectification has instantaneous and time-dependent components. The time-dependent increase in the K conductance for the negative voltage pulse as well as the decrease in the conductance for the positive pulse follows first-order kinetics. The steady-state conductance increases as the membrane potential becomes more negative and reaches the saturation value at about -40 mV more negative than the K equilibrium potential, V(K). The entire K conductance can be expressed by g(K).n; g g(K) represents the component for the time-independent conductance which depends on V-V(K) and [K+]o, and n is a dimensionless number (1 is greater than or equal to n is greater than or equal to 0) and determined by two rate constants which depend only on V-V(K). Cs+ does not carry any significant current through the K channel but blocks the channel at low concentration in the external medium. The blocking effect increases as the membrane potential is made more negative and the potential-dependent blocking by the external Cs+ also has instantaneous and time-dependent components.

scholarly journals Voltage clamp analysis of two inward current mechanisms in the egg cell membrane of a starfish.

1975 ◽  
Vol 65 (5) ◽  
pp. 617-644 ◽  
Author(s):  
S Hagiwara ◽  
S Ozawa ◽  
O Sand
Keyword(s):  
Membrane Potential ◽  
Cell Membrane ◽  
Voltage Clamp ◽  
Time Course ◽  
Experimental Result ◽  
Egg Cell ◽  
Ca Channel ◽  
Inward Current ◽  
Ionic Mechanisms ◽  
The Relationship

Ionic mechanisms of excitation were studied in the immature egg cell membrane of a starfish, Mediaster aequalis, by analyzing membrane currents during voltage clamp. The cell membrane shows two different inward current mechanisms. One is activated at a membrane potential of -55 approximately -50 mV and the other at -7 approximately -6 mV. They are referred to as channels I and II, respectively. A similar difference is also found in the membrane potential of half inactivation. Currents of the two channels can, therefore, be separated by selective inactivation. The currents of both channels depend on Ca++ (Sr++ or Ba++) but only the current of channel I depends on Na+. The time-course of current differs significantly between the two channels when compared at the same membrane potential. The relationship between the membrane current and the concentration of the permeant ions is also different between the two channels. The result suggests that channel II is a more saturable system. The sensitivity of the current to blocking cations such as Co++ or Mg++ is substantially greater in channel II than in channel I. Currents of both channels depend on the external pH with an apparent pK of 5.6. They are insensitive to 3 muM tetrodotoxin (TTX) but are eliminated totally by 7.3 mM procaine. The properties of channel II are similar to those of the Ca channel found in various adult tissues. The properties of channel I differ, however, from those of either the typical Ca or Na channels. Although the current of the channel depends on the external Na the amplitude of the Na current decreases not only with the Na concentration but also with the Ca concentration. No selectivity is found among Li+, Na+, Rb+, and Cs+. The experimental result suggests that Na+ does not carry current but modifies the current carried by Ca in channel I.

scholarly journals Electrical excitability in the egg cell membrane of the tunicate

1974 ◽  
Vol 238 (1) ◽  
pp. 37-54 ◽  
Author(s):  
Shun-Ichi Miyazaki ◽  
Kunitaro Takahashi ◽  
Kazuko Tsuda
Keyword(s):  
Cell Membrane ◽  
Egg Cell ◽  
Electrical Excitability
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