ADRENOCORTICOTROPIC HORMONE STIMULATES A TRANSIENT CALCIUM-UPTAKE IN RAT LYMPHOCYTES

Freshly isolated rat lymphocytes were tested for corticotropin (ACTH)- dependent calcium uptake. Physiological levels of corticotropin (0.01- 1 nM) were found to stimulate both an uptake of Ca-45(2+) and a rise i n cAMP. The calcium uptake was delayed by 2 min after ACTH addition, b ut was rapid and transient after the onset of uptake. The extent of ca lcium uptake was dose dependent on the corticotropin concentration and reached a maximum by 1 nM. Several fragments of corticotropin were te sted for activity; both full-length 1-39 and a functional truncated fo rm, 1-25, had equivalent effects on Ca-45 influx at 1 nM; however, alp ha MSH-(1-13), ACTH-(11-24), or a mixture of alpha MSH and ACTH-(11-24 ) had no effect on Ca-45 influx. Extracellular calcium uptake was bloc ked by the calcium channel blockers lanthanum, diltiazem, nifedipine, and omega-conotoxin. Splenic lymphocytes that express ACTH receptors h ad ligand-dependent calcium uptake, but thymocytes that lack ACTH rece ptors had no ligand-dependent calcium uptake. A mouse adrenal cell lin e, Y-1, showed the same Ca-45 uptake kinetics. These findings demonstr ate that both lymphocytes and adrenal cells have a functional ACTH-dep endent calcium uptake mechanism.