The mechanism by which arginine stimulates Ca2+ inflow into the pancreatic B cell was investigated. Arginine (10 mM) increased 86Rb outflow from perifused rat pancreatic islets, suggesting that arginine-stimulated Ca2+ influx into the B cell does not result from a decrease in K+ conductance. Arginine stimulated Ca2+ uptake in isolated islets over short incubation periods and increased 45Ca outflow from perifused islets in a Ca2+-dependent manner. The calcium channel blocker verapamil inhibited both arginine-stimulated 45Ca uptake and 45Ca outflow. However, the sensitivity toward verapamil of arginine-stimulated islets was lower than that of islets stimulated by 20 mM K+, which gates voltage-sensitive Ca2+ channels. It was similar to that of islets stimulated by 8.3 mM glucose, which is thought to mainly gate voltage-insensitive Ca2+ channels. It is suggested that arginine stimulates Ca2+ inflow into the B cell by gating voltage-insensitive Ca2+ channels. The arginine-induced stimulation of Ca2+ inflow could participate in the depolarizing action of the amino acid on the B cell membrane.