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Ca and Na inward currents were recorded upon depolarizations in Euplotes after the blockage of K outward currents with intracellular Cs ions. The Na current was analyzed under voltage clamp and had the following properties: it activated to a maximum within 150 msec and partly inactivated during sustained voltage steps. It had a positive equilibrium potential between 25 and 30 mV and could be carried by Na or Li ions but not by K, choline or Tris ions. The current revealed a prominent associated inward tail current which deactivated with a single-exponential time constant of 118 msec. Both the current and its tail were strongly reduced after reduction of the extracellular Na concentration. Externally applied K channel blocker tetraethylammonium chloride did not block the current. Either EGTA injection into the cell or nonlethal deciliation with ethanol eliminated the current and its tail. These results indicate the existence of a Na conductance within the membrane of Euplotes which is activated by the intracellular level of free Ca2+. [ABSTRACT FROM AUTHOR]

A newly discovered recessive mutation, clk, in the marine ciliate Euplotes vannus is responsible for induction of intraclonal conjugation at low, i.e. <2 instead of 10 mM [K]. Heredity was assured by crosses to standard clones and by backcrosses. Pairing in clk clones is prevented by K at 2 mM, by Rb and Cs and Cs at 4 mM, not by Li, NH, and TEA up to 10 mM. Clones with the clk phenotype were found in several natural populations. [ABSTRACT FROM AUTHOR]

Copyright of Experientia is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Experientia is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In two strains of C. convexus, an Isopod which is known to be sex-determined by a polygenic system, monofactorial sex determination has been found. This is considered to be the result of an evolutionary step from polygenic to gonosomal sex determination within the species. [ABSTRACT FROM AUTHOR]

In the marine hypotrichous ciliate Euplotes vannus, the transient K+ outward current, IK fast, was studied by use of a single-microelectrode voltage-clamp equipment. Activation and inactivation kinetics, and steady-state inactivation are comparable to the properties of A-currents. Not typical for this type of current is its insensitivity to either 4-AP or 3,4-AP and its Ca2+ dependence which was derived from its inhibition by either extracellular Cd2+, La3+, D-600, or by intracellular BAPTA. Actual amplitudes of IK fast were obtained from a composite current, by subtraction of early parts of a slowly activating K+ current, IK slow, and of the early, transient Ca2+ inward current, ICa fast, that is typical for ciliates. IK fast counteracts ICa fast during the first milliseconds after onset of depolarization such that the composite current is purely outward directed.

Electrical properties of E. vannus were investigated by use of constant current injection, voltage-clamp, and isoosmotic ion substitution. The resting potential of approximately -40 mV was K(+) and Ca(2+)-dependent. Spontaneous depolarizations occurred frequently with peaks around -20 mV and durations from several hundred ms to several s. External Ba(2+) or internal Cs(+) induced all-or-none action potentials. Current stimuli induced Ca(2+)-dependent graded action potentials. Sr(2+) or Ba(2+), but not Mg(2+), instead of Ca(2+) increased the regenerative response. Repolarization occurred in two steps: a first fast and a second slow one. It was strongly modified by the Ca(2+) substitutes. A voltage-dependent small Ca(2+) inward current was activated at depolarizations beyond -20 mV. It triggered a fast and a slowly activating K(+) outward current and was itself short-circuited by the fast K(+) current. Therefore, it could only be measured when K(+) currents were not activated or inhibited. A slowly activating Na(+) inward current was identified that turned to outward direction after replacement of external Na(+) by choline(+). The K(+) outward currents differed in their sensitivity to external TEA(+) and in their inactivation kinetics. All currents were correlated to the voltage-dependent influx of Ca(2+)., (Copyright © 1988 Gustav Fischer Verlag · Stuttgart · New York. Published by Elsevier GmbH.. All rights reserved.)