title: Characterization of oscillations in cytosolic free Ca2+ concentration and measurement of cytosolic Na+ concentration changes evoked by angiotensin II and vasopressin in individual rat aortic smooth muscle cells. Use of microfluorometry and digital imaging.
abstract: Dual wavelength microfluorometry was used to characterize the changes in cytosolic free Ca2+ concentration [( Ca2+]i) in individual cultured rat aortic vascular smooth muscle cells (VSMC). Angiotensin II (ANG II) at 10(-8) M induced a transient rise in [Ca2+]i from 43 +/- 2 to 245 +/- 23 nM, lasting for approximately 60 s (n = 42). In half of the population, discrete oscillations in [Ca2+]i of smaller amplitude occurred after the initial [Ca2+]i peak, with a period of 58 +/- 8 s and a maximum height of 132 +/- 24 nM. A similar oscillatory pattern was observed with arginine vasopressin (AVP). The oscillations depended upon the presence of extracellular Ca2+. Cytosolic free Na+ concentration ([Na+]i) in VSMC was also measured using the fluorescent Na+ probe sodium-binding benzofuran isophthalate. ANG II induced a gradual and sustained elevation of [Na+]i, from 24.0 +/- 6.2 to 36 +/- 9.7 mM. In response to AVP, [Na+]i rose to 41.0 +/- 11.6 mM. Video imaging of individual VSMC, with on-line ratio calibration of [Ca2+]i, revealed an inhomogeneous distribution of Ca2+ within the cell. [Ca2+] in the nucleus was invariably lower than in the cytoplasm in resting cells. In the cytoplasm, there were small regions in which [Ca2+] was elevated, or "hot spots." In Ca(2+)-containing medium, the initial rise in [Ca2+]i triggered by ANG II and AVP appeared to emanate from the hot spots and to spread evenly throughout the cytoplasm. Between [Ca2+]i oscillations, Ca2+ retreated back to the original hot spots. This study demonstrates the cellular and subcellular heterogeneity of [Ca2+]i both in resting VSMC and during stimulation by ANG II and AVP and reports the direct measurement of [Na+]i in VSMC. The results suggest an action of Ca2+ in both the initial and sustained phases of the response in VSMC and a link between changes in [Ca2+]i and [Na+]i.
authors.affiliation: Department of Medicine, University Hospital, Geneva, Switzerland.
authors.forename: E M
authors.initials: EM
authors.lastname: Johnson
authors.forename: J M
authors.initials: JM
authors.lastname: Theler
authors.forename: A M
authors.initials: AM
authors.lastname: Capponi
authors.forename: M B
authors.initials: MB
authors.lastname: Vallotton
mesh_terms: D000804:Angiotensin II / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003592:Cytophotometry; D016257:Fura-2; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D014667:Vasopressins / Q000378:metabolism*
chemical_list: D014667:Vasopressins; D000804:Angiotensin II; D012964:Sodium; D002118:Calcium; D016257:Fura-2