A comparison of the lanthanum and EGTA methods for measuring calcium influx into vascular smooth muscle cells.

A comparison has been made of methods utilizing LaCl3 or EGTA for the determination of changes in Ca2+ influx into vascular smooth muscle. Stimulation of 45Ca2+ influx through voltage-operated channels using KCl and blockade of this effect with verapamil were used as test stimuli. Satisfactory results were obtained using ice-cold, Ca2+-free wash solutions containing LaCl3 (10-80.8 mmole.l-1). To achieve a rate of 45Ca2+ exchange of approximately 1% min-1, a wash duration of 60-90 min, depending on the tissue, was necessary. Using an EGTA wash less 45Ca2+ was retained by the tissue and the rate of 45Ca2+ exchange was greater than when LaCl3 was used. However, the changes in 45Ca2+ influx produced by the test stimuli and detected following an EGTA wash were qualitatively similar to those obtained when LaCl3 was used.