Ultrastructural and mechanical properties of electrically inexcitable skeletal muscle fibers of the crustacean Atya lanipes.
Examination of the ultrastructure and mechanical activation of the ventro-abdominal flexor muscle of the freshwater crustacean Atya lanipes shows that the fibers are of the long sarcomere, tonic type. The fibers possess an ample and well-organized internal membrane system, with extensive regions of T/SR dyad contacts near the ends of the A bands. An orbit of 10-12 thin filaments surrounds each thick filament. The lanthanum tracer method reveals a highly regular organization of the T-system, Z-tubules, and multiple internal clefts. Tension generation responds to extracellular potassium in a concentration dependent manner and is very slow. Mechanical activation is strictly dependent on extracellular Ca2+, even though these muscle fibers do not generate Ca2+ currents when depolarized. Tension development responds to caffeine and is also dependent on extracellular Na+, suggesting that Ca2+ release from the SR and Ca2+ influx via the Na/Ca exchanger intervene in mechanical activation.
Bonilla
M
M
Department of Physiology and Biophysics, ENCB del IPN, Mexico, D.F.
García
M C
MC
Orkand
P M
PM
Zuazaga
C
C
D000818:Animals; D002110:Caffeine; D002118:Calcium / Q000502:physiology; D003445:Crustacea / Q000502:physiology*; D004558:Electric Stimulation; D008564:Membrane Potentials; D009132:Muscles / Q000502:physiology* / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure
D002110:Caffeine; D002118:Calcium