Effects of cationic modification on 45Ca uptake and insulin release by transplantable rat insulinoma cells maintained in tissue culture

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1. 1. Acute effects of cations on 45Ca uptake and insulin release by transplantable rat insulinoma cells were examined after 2–3 days culture in RPMI-1640 containing 11.1 mM glucose. 2. 2. At 2.6 mM Ca 2+, rat insulinoma cells (>95% viability) released 78–158 ng insulin/10 6 cells during 60 min incubation with uptake at 2.19–3.24 nmol 45Ca/10 6 cells. 3. 3. Addition of 2 mM La 3+, Co 2+, Mn 2+, Zn 2+ or Ba 2+ did not affect 45Ca uptake. Insulin release was also unaffected by these cations with the exception of 87% inhibition in the presence of La 3+ or Zn 2+. 4. 4. Omission of 5.9 mM K +, 1.2 mM Mg 2+, 115 mM Na + or H + (pH 8.5) did not affect 45Ca uptake or insulin release, irrespective of osmotic compensation using choline chloride or sucrose. Rat insulinoma cells were similarly unresponsive to addition of 30.9 mM K +, 12 mM Mg 2+ or H + (pH 6.3). 5. 5. Omission of 2.6 mM Ca 2+ (with or without addition of 1 mM EGTA) or addition of 20.5 mM Ca 2+ did not affect insulin release. 6. 6. The results indicate that rat insulinoma cells are little affected by cationic modifications which have profound effects on Ca 2+ handling and insulin release by pancreatic β-cells. Dysregulation of insulin release by insulinoma cells is associated with marked irregularities in the control of transmembrane Ca 2+ fluxes and sensitivity to extracellular Ca 2+.