The superficial buffer barrier in vascular smooth muscle.
Force development and fura-2 fluorescence were simultaneously measured in the rabbit inferior vena cava. Discharging SR Ca2+ with either caffeine or norepinephrine prior to stimulation of Ca2+ influx induced a delay of 30-70 s between the intracellular Ca2+ signal and development of force. This delay was abolished by the application of caffeine. These data support the superficial buffer barrier hypothesis, which holds that Ca2+ entry from the extracellular space proceeds via a restricted cytoplasmic region between the inner plasmalemmal surface and the peripheral sarcoplasmic reticulum (SR). Ca2+ accumulation by this SR fraction appears to be able to delay Ca2+ entry into the deeper myoplasm where it activates the myofilaments. Caffeine and thapsigargin elevated the steady-state [Ca2+]i, suggesting a contribution by the SR Ca2+ pump to Ca2+ extrusion from the cells. Norepinephrine enhanced myofilament Ca2+ sensitivity, while caffeine decreased it.
Chen
Q
Q
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, FL 33101.
Cannell
M
M
van Breemen
C
C
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002132:Calcium Radioisotopes; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D016257:Fura-2; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin; D014682:Vena Cava, Inferior / Q000378:metabolism
D002132:Calcium Radioisotopes; D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2