Relaxation of chemically skinned guinea pig taenia coli smooth muscle from rigor by photolytic release of adenosine-5'-triphosphate.
The mechanical events following release of ATP from P3-1-(2-nitro)phenylethyladenosine-5'-triphosphate (caged-ATP) in skinned guinea pig taenia coli smooth muscle in rigor were investigated. A rigor force of about 25-35% of the maximal active force was obtained by removing ATP at the plateau of a maximal active contraction. In the rigor solution free-Mg2+ was 2 mM, ionic strength 90 mM and pH 7.0. When caged-ATP (12.5 mM) was diffused into the preparation there was no change in the rigor force. Photolytic production of about 2 mM ATP was achieved with a xenon flash lamp. Following illumination, force decreased with an approximate initial rate constant of 0.7 s-1. The rate of relaxation was increased in the presence of inorganic phosphate (at 3 mM: 1.3 s-1; 10 mM: 2.2 s-1). At higher Mg2+ concentrations the rate of relaxation was slower (5 mM: 0.2 s-1) and at lower concentrations the rate was faster (0.5 mM: 1.2 s-1). An increased rate of relaxation was observed when ionic strength was increased to 150 mM (2.2 s-1). Phosphate increased the rate of relaxation at the different levels of Mg2+ (0.5-10 mM) and ionic strength (90, 150 mM). In preparations shortened (by 1-3%) to give reduced rigor force, a small transient increase in tension was recorded after ATP release. In comparison to the rates of ATP-induced dissociation of actomyosin in solution, reported in the literature, the rate of relaxation from rigor is slower. This may reflect a slow rigor cross-bridge dissociation or mechanical interactions not associated with cross-bridges in the muscle fibre.(ABSTRACT TRUNCATED AT 250 WORDS)
Physiologisches Institut der Universität Heidelberg, F.R.G.
A
A
Arner
R S
RS
Goody
G
G
Rapp
J C
JC
Rüegg
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009130:Muscle, Smooth / Q000378:metabolism*; D010782:Photolysis
C029273:P(3)-1-(2-nitro)phenylethyladenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D008274:Magnesium