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

Glucose-induced insulin release, glucose-induced rises in intracellular free Ca2+ concentration ([Ca2+](i)), and voltage-dependent Ca2+ channel 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 fetal rat beta-cells. Voltage-dependent Ca2+ channel antagonists decreased 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 presence of nifedipine-sensitive, voltage-dependent Ca2+ channels was demonstrated directly by measuring Ca2+ currents using the whole-cell configuration 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 glucose stimulation to Ca2+ influx is essentially mature, in contrast to what has been reported for fetal or very early neonatal cells.