INSULIN-SECRETION AND INTRACELLULAR CA2-CULTURES OF NEONATAL RAT BETA-CELLS( RISES IN MONOLAYER)

Glucose-induced insulin release, glucose-induced rises in intracellula r free Ca2+ concentration ([Ca2+](i)), and voltage-dependent Ca2+ chan nel activity were assessed in monolayer cultures of beta-cells from 3- 5-day-old rats. The glucose-stimulated insulin secretory responses and [Ca2+](i) rises were like those in adult rat beta-cells rather than f etal rat beta-cells. Voltage-dependent Ca2+ channel antagonists decrea sed glucose-induced insulin secretion, aborted the [Ca2+](i) rise and, like deprivation of extracellular Ca2+, prevented the glucose-induced rise in [Ca2+](i) when added before the glucose challenge. The presen ce of nifedipine-sensitive, voltage-dependent Ca2+ channels was demons trated directly by measuring Ca2+ currents using the whole-cell config uration of the patch-clamp technique and indirectly by measuring [Ca2](i) after membrane depolarization by 45 mM K+ or 200 mu M tolbutamide . Thus, in cultured beta-cells of 3-5-day-old rats the coupling of glu cose stimulation to Ca2+ influx is essentially mature, in contrast to what has been reported for fetal or very early neonatal cells.