PT  - JOURNAL ARTICLE
AU  - T Reisine
AU  - H L Wang
AU  - S Guild
TI  - Somatostatin inhibits cAMP-dependent and cAMP-independent calcium influx in the clonal pituitary tumor cell line AtT-20 through the same receptor population.
DP  - 1988 Apr 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 225--231
VI  - 245
IP  - 1
4099  - http://jpet.aspetjournals.org/content/245/1/225.short
4100  - http://jpet.aspetjournals.org/content/245/1/225.full
SO  - J Pharmacol Exp Ther1988 Apr 01; 245
AB  - The characteristics of somatostatin (SRIF) inhibition of calcium influx stimulated by corticotropin releasing factor (CRF), an activator of adenylate cyclase, and K+, a membrane depolarizing agent, in AtT-20 cells were assessed. Changes in cytosolic calcium levels were measured using the fluorescence probe Quin 2. Both CRF and K+ raise cytosolic calcium levels by stimulating calcium influx. SRIF induced an immediate inhibition of CRF and K+-stimulated calcium influx. This effect was concentration-dependent with IC50 values for SRIF's blockade of CRF and K+ stimulation of 64 +/- 13 pM and 100 +/- 15 pM, respectively. The SRIF analogs, SRIF 28, Trp8-SRIF and Tyr11-SRIF had the same rank order of potency to block CRF and K+-induced calcium influx. The inhibitory effects of SRIF on AtT-20 cells were abolished by pertussis toxin pretreatment. SRIF inhibition of both CRF and K+-induced calcium influx desensitized. The desensitization was rapid (T1/2 approximately 2.5 min), dependent on the concentration of SRIF and not due to the degradation of the peptide. The ability of SRIF to block CRF (cyclic AMP-dependent) and K+ (cyclic AMP-independent)-stimulated calcium influx into AtT-20 cells cannot be separated.