Abstract: | We previouslydemonstrated, using rat PC-12 pheochromocytoma cells differentiated toa sympathetic neuronal phenotype with nerve growth factor (NGF), thatneuropeptide Y (NPY) inhibits catecholamine synthesis as well asrelease. Inquiry into the mechanisms of these inhibitions implicateddistinct pathways involving reduction ofCa2+ influx throughvoltage-activated Ca2+ channels.In the present investigation the effects of NPY on whole cellBa2+ currents were examined toobtain direct evidence supporting the mechanisms suggested by thosestudies. NPY was found to inhibit the voltage-activatedBa2+ current in NGF-differentiatedPC-12 cells in a reversible fashion with anEC50 of 13 nM. This inhibition waspertussis toxin sensitive and resulted from NPY modulation of L- andN-type Ca2+ channels. Theinhibition of L-type channels was not seen with <1 nM freeintracellular Ca2+ or when proteinkinase C (PKC) was inhibited by chelerythrine or PKC-(1931).Furthermore, the effect of NPY on L-type channels was mimicked by thePKC activator phorbol 12-myristate 13-acetate. These studiesdemonstrate that, in addition to inhibition of N-type Ca2+ channels, inNGF-differentiated PC-12 cells NPY inhibits L-type Ca2+ channels via an intracellularCa2+- and PKC-dependent pathway. |