Effects of the intracellular Ca ion concentration upon the excitability of the muscle fiber membrane of a barnacle.
The membrane excitability and contraction were examined in single barnacle muscle fibers with different internal Ca(++) concentrations by using buffer solutions made up with EGTA and Ca-gluconate in various proportions. During the passage of dc currents the membrane shows all-or-none spike potentials for internal Ca(++) concentrations below about 8 x 10(-8)M, oscillatory potential changes in the range between 8 x 10(-8) to 5 x 10(-7)M, but neither oscillatory nor spike potentials were seen for concentrations above 5 x 10(-7)M. All-or-none spike potentials were suppressed when the internal Mg(++) concentration exceeded 5 mM. The suppression threshold of the internal Ca(++) concentration for the Sr spike is much higher than that for the Ca spike. The threshold concentration of internal Ca(++) for contraction was about 8 x 10(-7)M.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology*; D002614:Chelating Agents / Q000494:pharmacology; D003445:Crustacea; D004594:Electrophysiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D009132:Muscles / Q000166:cytology / Q000502:physiology*
D002614:Chelating Agents; D008274:Magnesium; D002118:Calcium