Measurement of cytoplasmic calcium in single microvessels with increased permeability.
We investigated the hypothesis that an increase in cytoplasmic calcium ion concentration, [Ca2+]i, is one of the mechanisms responsible for increased microvessel permeability. We loaded the cells forming the walls of individually perfused microvessels in frog mesentery with fura-2 and measured [Ca2+]i in the control state and after adding the Ca2+ ionophore ionomycin to the perfusate. [Ca2+]i in the control state was 65 +/- 6 nM and increased to an initial peak of 285 +/- 29 nM after 1-3 min. After 4, 6, and 10 min, [Ca2+]i was 199 +/- 18, 163 +/- 16, and 129 +/- 9 nM, respectively. [Ca2+]i fell back to 77 +/- 7 nM after ionophore was removed. In similar experiments, hydraulic conductivity (Lp) increased to a peak of 9.5 times control after 1-3 min, then fell to 2.0 times control after 6 min. Lp remained elevated at this level for as long as ionophore was present in the perfusate. [Ca2+]i modulates the initial and sustained phases of the permeability increase. Both processes depend on external Ca2+ influx. Our experiments provide the first direct measurement of [Ca2+]i during a change in the permeability of an intact microvessel.
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Department of Human Physiology, School of Medicine, University of California, Davis 95616.
Pagakis
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Curry
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D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002196:Capillaries / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D002199:Capillary Permeability; D003593:Cytoplasm / Q000378:metabolism*; D000431:Ethanol / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D015759:Ionomycin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009994:Osmolar Concentration; D010827:Physiology / Q000295:instrumentation; D011894:Rana pipiens; D013997:Time Factors; D014680:Veins / Q000378:metabolism*; D014699:Venules / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure
D001572:Benzofurans; D005456:Fluorescent Dyes; D000431:Ethanol; D015759:Ionomycin; D008274:Magnesium; D002118:Calcium; D016257:Fura-2