Measurements were made of (45)Ca influx into isolated internodal cells of Chara corallina and also into internodal cells of intact plants. (45)Ca influx was closely related to growth. In rapidly expanding internodal cells, the influx was approximately 1.4 nmol m(-2) s(-1) compared to the influx in mature cells from slow-growing cultures of 0.2 nmol m(-2) s(-1). Isolated internodal cells had influxes in the range 0.2 to 0.7 nmol m(-2) s(-1), but this increased to approximately 2 nmol m(-2) s(-1) in high calcium solutions and to 4 nmol m(-2) s(-1) in high potassium solutions. No significant effects on calcium influx were observed for changes in external pH or for treatments that changed internal pH, except that NH(4) was slightly inhibitory. Severe metabolic inhibition by carbonylcyanide-m-chlorophenyl-hydrazone stimulated influx, whereas dicyclohexylcarbodiimide had no effect and darkness inhibited influx. La(3+) also inhibited influx, but the organic channel blockers nifedipine and bepridil stimulated influx. Verapamil had no effect. The results are generally consistent with voltage regulation of calcium channels as in animal cells.