Somatostatin blocks a calcium current in acutely isolated adult rat superior cervical ganglion neurons

Abstract

Somatostatin-like immunoreactivity has been reported to occur in the postganglionic neurons of sympathetic ganglia. We therefore investigated the effect of somatostatin (SOM) on the Ca 2+ current in sympathetic neurons. Voltage-clamp recordings, using the whole-cell patch-clamp technique, were made from acutely isolated adult rat superior cervical ganglion (SCG) neurons in solutions (external and internal) designed to isolate Ca 2+ currents. Application of 0.001–1.0 μM [ d-Trp 8]SOM resulted in a rapid, reversible and concentration-dependent decrease in the amplitude of the Ca 2+ current evoked from a holding potential of −80 mV. The concentration-response relationship for SOM could be fitted to a single-site binding model with an apparent dissociation constant of 11 nM; the maximal attainable block of Ca 2+ current by SOM was 50%. SOM also produced a pronounced slowing of the Ca 2+ current rising phase, especially at more depolarized potentials. At higher concentrations (0.03 1.0 μM), prolonged application of SOM resulted in a progressive decrease in blocking ability. The results are consistent with a neurotransmitter and/or neuromodulator role for SOM in the sympathetic nervous system.