Voltage-dependent calcium and potassium conductances in striated muscle fibers from the scorpion, Centruroides sculpturatus.
Ionic currents responsible for the action potential in scorpion muscle fibers were characterized using a three-intracellular microelectrode voltage clamp applied at the fiber ends (8-12 degrees C). Large calcium currents (ICa) trigger contractile activation in physiological saline (5 mM Ca) but can be studied in the absence of contractile activation in a low Ca saline (< or = 2.5 mM). Barium (Ba) ions (1.5-3 mM) support inward current but not contractile activation. Ca conductance kinetics are fast (time constant of 3 msec at 0 mV) and very voltage dependent, with steady-state conductance increasing e-fold in approximately 4 mV. Half-activation occurs at -25 mV. Neither ICa nor IBa show rapid inactivation, but a slow, voltage-dependent inactivation eliminates ICa at voltages positive to -40 mV. Kinetically, scorpion channels are more similar to L-type Ca channels in vertebrate cardiac muscle than to those in skeletal muscle. Outward K currents turn on more slowly and with a longer delay than do Ca currents, and K conductance rises less steeply with voltage (e-fold change in 10 mV; half-maximal level at 0 mV). K channels are blocked by externally applied tetraethylammonium and 3,4 diaminopyridine.
Gilly
W F
WF
Hopkins Marine Station, Stanford University, Pacific Grove, California 93950.
Scheuer
T
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D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000077770:Amifampridine; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D004558:Electric Stimulation; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008839:Microelectrodes; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000502:physiology*; D012605:Scorpions / Q000502:physiology*; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013997:Time Factors
D015220:Calcium Channels; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D001464:Barium; D019789:Tetraethylammonium; D015761:4-Aminopyridine; D000077770:Amifampridine; D011188:Potassium; D002118:Calcium