Somatostatin cyclic octapeptide analogs which preferentially bind to SOMa receptors block a calcium current in rat superior cervical ganglion neurons

Abstract

To characterize further the somastatin (SOM) receptor mediating Ca 2+ current reduction in rat superior cervical ganglion (SCG) neurons, the effects of three synthetic SOM octapeptide analogs, ▪ which bind preferentially to pituitary SOM receptors (SOMa) were investigated. Ca 2+ currents were recorded using the whole-cell variant of the patch-clamp technique from neurons isolated enzymatically from adult rat SCG. Application of the SOM analogs (0.003–3 μM) produced a rapid, reversible, and concentration-dependent decrease in Ca 2+ current amplitude in addition to slowing the rising phase of the Ca 2+ current. Estimates of the concentration producing half-maximal block (EC 50) and maximum attainable block ( B max) for DC 13–116, IM 4–28, and SMS 201–995 were 196, 67, and 9.5 nM, respectively, and 52, 57, and 48%, respectively. The results suggest that the SOM receptor on SCG neurons more closely resembles the SOMa receptor of the anterior pituitary than the SOMb receptor of cerebral cortical membranes.