sq-23377 and 1-4-dihydropyridine

Small cell lung carcinoma is an aggressive neuroendocrine tumor that secretes several hormones, some of which act as autocrine growth factors. In order to obtain more information on the process of hormone secretion from this tumor, we have studied the role of intracellular free Ca2+ concentrations and voltage-operated calcium channels in the control of [3H]serotonin release from in vitro growing cell lines. We found that the Ca2+ ionophore ionomycin and the Ca(2+)-ATPase antagonist thapsigargin induced a dose-dependent increase of intracellular Ca2+ and a parallel enhancement of [3H]serotonin release. KCl-induced depolarization also stimulated a dose- and Ca(2+)-dependent [3H]serotonin release that in the GLC8 cell line was effectively inhibited by Ca2+ channel antagonists (Cd2+, nitrendipine, verapamil, omega-conotoxin GVIA, and omega-agatoxin IVA) and potentiated by the Ca2+ channel agonist BayK8644. Autoantibodies against Ca2+ channels present in the sera of Lambert-Eaton myasthenic patients antagonized KCl- but not ionomycin-induced [3H]serotonin release. Polymerase chain reaction analysis indicated that GLC8 cells express L-, N-, and P-type neuronal Ca2+ channel alpha 1 subunits, together with two types of Ca2+ channel beta subunits. The presence of three functionally distinct high threshold Ca2+ channels was also revealed by patch clamp experiments; high threshold Ca2+ channels were identified as dihydropyridine-sensitive (L-type), omega-conotoxin GVIA-sensitive (N-type), and omega-agatoxin IVA-sensitive (P-type). Our data demonstrate that [3H]serotonin is released by small cell lung carcinoma cells in a Ca(2+)-dependent manner and that depolarization-induced [3H]serotonin release is mediated by Ca2+ influx through distinct, neuron-like, Ca2+ channel subtypes.

Topics: Autoantibodies; Base Sequence; Calcium Channel Blockers; Calcium Channels; Calcium-Transporting ATPases; Carcinoma, Small Cell; Dihydropyridines; DNA Primers; Fura-2; Humans; Ionomycin; Lambert-Eaton Myasthenic Syndrome; Lung Neoplasms; Molecular Sequence Data; omega-Conotoxin GVIA; Peptides; Potassium Chloride; Serotonin; Terpenes; Thapsigargin; Tritium; Tumor Cells, Cultured

The steroidogenic actions of angiotensin II (AII) and increased extracellular K+ concentrations [( K+]) in rat adrenal glomerulosa cells are selectively enhanced by the voltage-sensitive calcium channel agonist Bay K 8644 (BK 8644). The relationship between these effects of the dihydropyridine agonist and cytosolic calcium concentration [( Ca2+]i) was investigated in rat and bovine glomerulosa cells. In the rat glomerulosa cells, AII and increased [K+] elicited rapid elevations of [Ca2+]i with distinctive temporal characteristics. Whereas the [Ca2+]i response to [K+] declined to basal over 2-3 min, addition of 10 nM AII caused a biphasic increase in [Ca2+]i, with a rapid transient rise followed by a lower plateau phase that remained above basal for several minutes. BK 8644 alone did not affect [Ca2+]i, but at low concentrations (30 nM) increased the magnitude and duration of the [Ca2+]i response elicited by progressive elevation of extracellular [K+] to 12 mM. In AII-stimulated glomerulosa cells, 30 nM BK 8644 enhanced both phases of the cytosolic calcium response, with a more marked effect on the sustained plateau phase. In contrast to its prominent actions in rat glomerulosa cells, BK 8644 had no effect on AII-stimulated rises in [Ca2+]i in bovine glomerulosa cells, and only slightly enhanced their minor [Ca2+]i responses to potassium. These studies provide evidence that AII activates dihydropyridine-sensitive voltage-sensitive calcium channels in rat, but not bovine, adrenal glomerulosa cells. They also suggest that enhancement by BK 8644 of agonist-stimulated [Ca2+]i changes is responsible for its synergistic effects on aldosterone responses to potassium and AII in rat glomerulosa cells and emphasize the importance of the sustained phase of the cytosolic calcium signal in the steroidogenic action of AII.

Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Angiotensin II; Animals; Calcium; Calcium Channels; Cattle; Cytosol; Dihydropyridines; Ethers; Ionomycin; Kinetics; Male; Nifedipine; Potassium; Rats; Rats, Inbred Strains; Species Specificity; Spectrometry, Fluorescence; Zona Glomerulosa