ISSN:
1432-2013
Keywords:
Intracellular pH
;
Vascular smooth muscle
;
Chemically skinned muscle
;
Isometric force
;
20,000 Da myosin light chain phosphorylation
;
“Ca2+ jumps”
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The effects of pH (from pH values 6.50–7.10) on isometric tension development and relaxation were investigated in Triton X-100 “skinned” rat caudal artery. Helically cut skinned strips contracted in 21 μM Ca2+ were studied with respect to maximal isometric tension (Po) and rate of contraction (T0.5C), and following relaxation in 18 nm Ca2+, the rate of relaxation (T0.5R). Acidic pH (pH 6.50) decreased Po to 87% of isometric force obtained at pH 6.90, and increased the rate of contraction as shown by a decrease of T0.5C to 80%. In contrast, T0.5R increased 4.5-fold, indicating that with a change of only 0.40 pH units, relaxation rates were dramatically decreased. pCa-tension curves at pH values 6.50, 6.70, 6.90 and 7.10 indicated no significant shift in half maximal activation (pCa50) between pH 6.50 and 6.70, but a significant (P〈0.01) shift in pCa50 between pH 6.70 ([Ca2+]=0.46 μM) and pH 7.10 ([Ca2+]=0.87 μM). Compared to contractions at pH 6.90, myosin light chain (LC20) phosphorylation at pH 6.50 was significantly greater at 30 and 60 s into contraction but not significantly different at 3–10 min. At both pH 6.50 and 6.90, dephosphorylation was rapid and substantially preceded relaxation; LC20 dephosphorylation and relaxation occurred more rapidly at pH 6.90 than at 6.50. At pH 6.50 and 6.90, relax solutions made with increased Ca2+ buffering capacity showed no effect in enhancing T0.5R, suggesting the difference between relaxation rates was not due to Ca2+ diffusion limitations from the skinned strip. We suggest pH changes can after the contractile and relaxation responses in vascular smooth muscle and these effects may be related to LC20 phosphorylation/dephosphorylation regulatory mechanisms.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00582502
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