Measurement of cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle using aequorin.
The cytoplasmic free Ca2+ concentration in bovine tracheal smooth muscle strips was measured using aequorin. Carbachol induces a rapid rise in aequorin luminescence, which reaches a peak within 1-2 min and then falls to a plateau level in 5-6 min. This plateau gradually declines but remains significantly above the base-line value after 2 h. The initial Ca2+ transient is due to Ca2+ mobilization from an intracellular caffeine-sensitive pool. The plateau appears to be due to Ca2+ influx. Histamine or 5-hydroxytryptamine (serotonin) also induce a Ca2+ transient followed by a plateau phase which is lower than that induced by carbachol. The isometric tension generated by either of these two agonists shows a gradual decline in contrast to the sustained plateau seen in the carbachol-induced contraction. Extracellular high K+ induces a dose-dependent increase in aequorin luminescence that is totally due to Ca2+ influx across the plasma membrane and is greatly inhibited by a Ca2+-channel antagonist, nimodipine. These results suggest that two temporally and spatially different Ca2+-dependent mechanisms are involved in carbachol-induced tracheal smooth muscle contraction.
Takuwa
Y
Y
Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06510.
Takuwa
N
N
Rasmussen
H
H
D000331:Aequorin; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D003593:Cytoplasm / Q000378:metabolism; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008163:Luminescent Measurements; D008164:Luminescent Proteins; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D014132:Trachea
D002121:Calcium Channel Blockers; D008164:Luminescent Proteins; D010703:Phorbol Esters; D012701:Serotonin; D002110:Caffeine; D000331:Aequorin; D001285:Atropine; D006632:Histamine; D002217:Carbachol; D011188:Potassium; D002118:Calcium