Concentration-dependence of acetylcholine-induced changes in calcium and tension in swine trachealis.
Acetylcholine (ACh)-induced increases in intracellular calcium concentration ([Ca++]i) and tension were measured simultaneously in swine tracheal smooth muscle strips loaded with the calcium-sensitive fluorescent dye Fura-2. ACh at concentrations greater than or equal to 3 x 10(-8) M induced concentration-dependent increases in tension which reached a maximum at 10(-4) M. Increases in [Ca++]i occurred at all [ACh] tested (10(-8) to 10(-4) M). After addition of ACh at concentrations greater than 3 x 10(-7) M, [Ca++]i increased rapidly to a concentration dependent-peak then declined to a concentration-independent steady state approximately 250 nM above the resting [Ca++]i of 257 +/- 12 nM. There was a steep relationship (slope factor greater than 3) between the peak tension and the peak [Ca++]i reached at each [ACh]. The rate of decline of [Ca++]i to the steady state at [ACh] greater than 73 x 10(-7) M was well correlated with the peak [Ca++]i reached. We conclude that the peak increase in calcium induced by ACh sets the level of tension to be attained and the rate of decline of the transient increase in [Ca++]i. The steady-state [Ca++]i is sufficient for maintenance of tension.
Shieh
C C
CC
Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson.
Petrini
M F
MF
Dwyer
T M
TM
Farley
J M
JM
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D016257:Fura-2; D007424:Intracellular Fluid / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D013552:Swine; D013997:Time Factors; D014132:Trachea / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology
D000109:Acetylcholine; D002118:Calcium; D016257:Fura-2