Role of myosin phosphorylation and [Ca2+]i in myogenic reactivity and arteriolar tone.
The aim of this study was to define the relationship between intraluminal pressure, intracellular calcium concentration ([Ca2+]i), and myosin light-chain (MLC) phosphorylation in isolated arterioles exhibiting myogenic tone. Cremaster muscles were removed from anesthetized rats, and arterioles (approximately 100-microns diam) were dissected from surrounding tissues and cannulated on glass pipettes. Vessels were warmed to 34 degrees C and initially pressurized to 70 mmHg in the absence of intraluminal flow. For [Ca2+]i measurements, vessels were loaded with 5 microM fura 2, and fluorescence emitted by excitation at 340 and 380 nm was measured. Data were considered in terms of changes in the fluorescence ratio (340/380 nm) and collected at steady-state intraluminal pressures between 30 and 170 mmHg. For measurement of MLC phosphorylation, vessels were frozen in acetone-dry ice followed by sonication in homogenizing buffer. Homogenates were separated by two-dimensional gel electrophoresis, and proteins were visualized by silver staining. MLC phosphorylation was quantitated photodensitometrically, and results are expressed as percent total 20-kDa MLC. Increasing intraluminal pressure resultedin significant constriction with increased [Ca2+]i and MLC phosphorylation. For example, the fluorescence ratio was 0.80 +/- 0.04 at 30 mmHg compared with 1.02 +/- 0.05 at 120 mmHg (n = 7 vessels); corresponding MLC-phosphorylation values were 27.7 +/- 1.6 and 39.6 +/- 3.0% (n = 6). MLC phosphorylation in arterioles superfused with 0 mM Ca(2+)-2 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) was 8.5 +/- 0.7%.(ABSTRACT TRUNCATED AT 250 WORDS)
Zou
H
H
Department of Physiology, Eastern Virginia Medical School, Norfolk 23501, USA.
Ratz
P H
PH
Hill
M A
MA
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D001381:Azepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006706:Homeostasis; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors; D009281:Naphthalenes / Q000494:pharmacology; D009994:Osmolar Concentration; D010766:Phosphorylation; D011312:Pressure; D051381:Rats; D017207:Rats, Sprague-Dawley; D014666:Vasomotor System / Q000187:drug effects / Q000502:physiology*
D001381:Azepines; D018994:Myosin Light Chains; D009281:Naphthalenes; C070571:ML 7; D009219:Myosin-Light-Chain Kinase; D002118:Calcium