Somatostatin cyclic octapeptide analogs which preferentially bind to SOMa receptors block a calcium current in rat superior cervical ganglion neurons.
To characterize further the somastatin (SOM) receptor mediating Ca2+ current reduction in rat superior cervical ganglion (SCG) neurons, the effects of three synthetic SOM octapeptide analogs, D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (IM-4-82), D-Nal-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH2 (DC 13-116), and D-Phe-Cys-Phe-D-Trp-Lys-Thr-Cys-Thr-OL (SMS 201-995), which bind preferentially to pituitary SOM receptors (SOMa) were investigated. Ca2+ 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 microM) produced a rapid, reversible, and concentration-dependent decrease in Ca2+ current amplitude in addition to slowing the rising phase of the Ca2+ current. Estimates of the concentration producing half-maximal block (EC50) and maximum attainable block (Bmax) 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.
Ikeda
S R
SR
Section of Electrophysiology, National Institute on Alcohol Abuse and Alcolism, Rockville, MD 20852.
Schofield
G G
GG
D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000502:physiology*; D002469:Cell Separation; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D015282:Octreotide / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D010456:Peptides, Cyclic; D051381:Rats; D011919:Rats, Inbred Strains; D017981:Receptors, Neurotransmitter / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D017481:Receptors, Somatostatin; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D010456:Peptides, Cyclic; D017981:Receptors, Neurotransmitter; D017481:Receptors, Somatostatin; C060347:lanreotide; D013004:Somatostatin; C053408:RC 121; D015282:Octreotide; D002118:Calcium