Acute effects of amino acids, hormones and drugs on transplantable rat insulinoma cells were examined after 2-3 days culture in RPMI-1640 (11.1 mM glucose) to eliminate necrotic cells and counter prior hypoglycaemia. 2. At 2.6 mM Ca2+, rat insulinoma cells (greater than 95% viability) released 48-97 ng insulin/10(6) cells during 60 min incubations with uptake of 1.0-1.8 nmol 45Ca/10(6) cells. 3. Insulin release and 45Ca uptake by rat insulinoma cells were not modified by arginine, leucine, 2-ketoisocaproate, tolbutamide, glibenclamide, somatostatin, adrenaline, noradrenaline, diazoxide or cyproheptadiene. 4. Responsiveness to acetylcholine (stimulation of insulin release and 45Ca uptake) and to GIP (stimulation of insulin release) was demonstrated. Thiol reagents (CMBS, CPDS and DTNB) and agents affecting microtubules-microfilaments (colchicine, vinblastine and cytochalasin B) enhanced insulin release. 5. The results suggest that rat insulinoma cells exhibit a generalized defect in the regulation of insulin release by nutrients, hormones and drugs which act in pancreatic B-cells by alteration of cellular Ca2+. Responsiveness to agents affecting insulin release through alternative mechanisms appears to be retained.
