PRESENCE OF CHLORIDE-FORMATE EXCHANGE IN VASCULAR SMOOTH-MUSCLE AND CARDIAC-CELLS

The presence of chloride-formate anion exchange in vascular smooth mus cle cells (VSMCs) and cardiac myocytes was investigated. Imposing an o utward chloride gradient in sarcolemmal microsomes isolated from canin e aorta stimulated [C-14]formate uptake compared with the absence of a chloride gradient (24.3 +/- 2.33 versus 9.8 +/- 1.41 pmol/mg protein for 30 seconds, P < .03) and induced transient uphill [C-14]formate up take. The chloride-formate exchange was significantly inhibited in the presence of 1 mmol/L 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) or furosemide (57% and 61%, respectively). Incubation of rat c ultured VSMCs in a medium containing [C-14]formate resulted in uptake of formate that was significantly DIDS and furosemide sensitive (79.34 +/- 2.47, 43.03 +/- 2.37, and 44.65 +/- 1.68 pmol/mg protein for 4 mi nutes in control, DIDS, and furosemide groups, respectively). Preincub ation of the VSMCs in chloride-free medium significantly reduced the D IDS-sensitive (36.31 versus 16.85 pmol/mg protein for 4 minutes, P < . 001) and furosemide-sensitive (34.72 versus 8.78 pmol/mg protein for 4 minutes, P < .001) [C-14]formate uptake. These results are compatible with the presence of chloride-formate exchange in VSMCs. Influx of [C -14]formate into sarcolemmal vesicles isolated from canine heart was s ignificantly higher in the presence of an outward chloride gradient th an in its absence (18.1 +/- 2.3 versus 9.6 +/- 1.7 pmol/mg protein for 30 seconds, P < .03), The chloride-formate exchange was significantly inhibited in the presence of 1 mmol/L DIDS or furosemide (41% and 52% , respectively). We conclude that the distribution of chloride-formate exchange may be more universal than previously suggested. The physiol ogical significance of this anion exchanger remains to be determined.