Potent antagonism by BIM‐23056 at the human recombinant somatostatin sst₅ receptor

We have investigated the effects of somatostatin (SRIF) and the linear octapeptide BIM‐23056 on changes in intracellular calcium ion concentration ([Ca²⁺]_i) and on the formation of inositol‐1, 4, 5‐trisphosphate (Ins(1, 4, 5)P₃) in CHO‐K***1 cells transfected with the human recombinant SRIF sst₅ receptor. SRIF elicited concentration‐dependent increases in [Ca²⁺]_i, with a pEC₅₀ of 7.02±0.06, while BIM‐23056 (1 × 10⁻⁷m) behaved not as an agonist but as a potent, surmountable antagonist of these increases in [Ca²⁺]_i. The SRIF concentration‐effect curve for increases in [Ca²⁺]_i was shifted rightward producing an estimated pK_B for the antagonist of 8.0. BIM‐23056 (1 × 10⁻⁷m) also significantly attenuated Ins(1, 4, 5)P₃ increases due to SRIF, but had no effect on either basal or uridine 5′‐triphosphate (UTP) (1 × 10⁻⁴m) stimulated increases in the levels of [Ca²⁺]_i or Ins(1, 4, 5)P₃.

DOI: 10.1111/j.1476-5381.1996.tb15423.x

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