In:
Circulation Research, Ovid Technologies (Wolters Kluwer Health), Vol. 76, No. 4 ( 1995-04), p. 530-535
Abstract:
Abstract The effect of long-term exposure to hypertonic medium on Na + -H + exchange activity was studied in cultured vascular smooth muscle (VSM) cells by using a combination of 22 Na + influx and pH measurement with the pH-sensitive dye BCECF. Incubation of VSM cells in high-osmolality medium (510 mOsm/L) for 48 hours significantly increased the acid-stimulated 22 Na + influx (control, 3.16±0.41 nmol/mg protein per minute; high osmolality, 6.40±0.66 nmol/mg protein per minute; P 〈 .01) and Na + -dependent pH i recovery (control, 0.29±0.06 pH/min; high osmolality, 0.65±0.13 pH/min; P 〈 .03). Activation of Na + -H + exchange was osmolality dependent and reached maximal stimulation at ≈700 mOsm/L. Na + -H + exchanger stimulation was independent of serum in the culture media. Na + -H + exchanger isoform (NHE-1) mRNA in VSM cells cultured in high-osmolality medium was unchanged from that in VSM cells cultured in control medium, indicating an absence of transcriptional regulation by high osmolality. Long-term high osmolality significantly increased protein kinase C (PKC) activity in cultured VSM cells, as assessed by phosphorylation of a PKC-specific substrate (control, 20.9±2.1 pmol phosphorylation/mg protein per minute; high osmolality, 33.6±2.9 pmol phosphorylation/mg protein per minute; P 〈 .01). Downregulation of PKC by preincubation of VSM cells with 0.1 μmol/L phorbol 12-myristate 13-acetate (PMA) prevented osmolality-induced stimulation of the Na + -H + exchanger (control plus PMA, 0.27±0.05 pH/min; high osmolality plus PMA, 0.33±0.08 pH/min; P 〉 .05). These results indicate that long-term exposure to hypertonic medium stimulates Na + -H + exchange activity in cultured VSM cells and that this effect is independent of antiporter gene expression regulation. The results further demonstrate that the stimulatory effect of osmolality on Na + -H + exchanger is mediated via posttranslational modification of the Na + -H + exchanger by chronic PKC activation. The Na + -H + exchanger may be involved in VSM cell volume regulation in long-term high osmolality.
Type of Medium:
Online Resource
ISSN:
0009-7330
,
1524-4571
DOI:
10.1161/01.RES.76.4.530
Language:
English
Publisher:
Ovid Technologies (Wolters Kluwer Health)
Publication Date:
1995
detail.hit.zdb_id:
1467838-X
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