Tubular localization of silent calcium channels in crustacean skeletal muscle fibers.
Ca2+-induced Ca2+ release (CICR) in the superficial abdominal flexor muscle of the crustacean Atya lanipes appears to be mediated by a local control mechanism similar to that of vertebrate cardiac muscle, but with an unusually high gain. Thus, Ca2+ influx increases sufficiently the local concentration of Ca2+ in the immediate vicinity of the sarcoplasmic reticulum Ca2+ release channels to trigger the highly amplified release of Ca2+ required for contraction, but is too low to generate a macroscopic inward current (i.e., the Ca2+ channels are silent). To determine the localization of the silent Ca2+ Channels, the mechanical, electrophysiological and ultrastructural properties of the muscle were examined before and after formamide treatment, a procedure that produces the disruption of transverse tubules of striated muscle. We found that tubular disruption decreased tension generation by about 90%; reduced inward current (measured as Vmax, the maximum rate of rise of Sr2+ action potentials) by about 80%; and decreased membrane capacitance by about 77%. The results suggest that ca. 80% of the silent Ca2+ channels are located in the tubular system. Thus, these studies provide further evidence to support the local control mechanism of CICR in crustacean skeletal muscle.
Monterrubio
J
J
Institute of Neurobiology, Department of Physiology, University of Puerto Rico, San Juan 00901, USA.
Ortiz
G
G
Orkand
P M
PM
Zuazaga
C
C
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000502:physiology* / Q000648:ultrastructure*; D003445:Crustacea; D066298:In Vitro Techniques; D018485:Muscle Fibers, Skeletal / Q000502:physiology* / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000502:physiology / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000502:physiology / Q000648:ultrastructure*
D015220:Calcium Channels