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On the role of extracellular calcium in triggering contraction in muscle fibres from barnacle under membrane potential control.
Author(s) -
Hidalgo J,
Luxoro M,
Rojas E
Publication year - 1979
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1979.sp012697
Subject(s) - depolarization , contraction (grammar) , biophysics , extracellular , intracellular , chemistry , membrane potential , calcium , anatomy , muscle contraction , biology , biochemistry , endocrinology , organic chemistry
1. Single giant barnacle muscle fibres from Megabalanus psittacus (Darwin) were used to establish the possible role of extracellular Ca2+ in triggering the contraction. 2. Peak tension p0 during twitches elicited by depolarizing voltage clamp pulses decreases after the removal of Ca2+ from the external saline. p0 becomes too small to measure after a few minutes, when the model‐estimated level of total intracellular Ca has been reduced to 99.5% of its original value and the extracellular Ca in the clefts and/or tubules to about 10%. 3. In fibres where the outward currents were blocked by internal perfusion with Cs+, the curves of the integral of the inward current versus membrane potential and of peak tension versus membrane potential follow a similar pattern. 4. When Ca2+ in the external saline was replaced by Ba2+ or Sr2+, no twitches were generated although depolarizing voltage clamp pulses induced large inward currents comparable to those measured when Ca2+ was present. 5. It is concluded that an increase in Ca2+ in the fibre during the Ca2+ inward current is a necessary condition for the triggering of the development of tension. The data on Ba2+ inhibition is consistent with the hypothesis that there are two different intracellular sites of action for Ca2+.