Urotensin‐II regulates intracellular calcium in dissociated rat spinal cord neurons

Urotensin‐II (U‐II), a peptide with multiple vascular effects, is detected in cholinergic neurons of the rat brainstem and spinal cord. Here, the effects of U‐II on [Ca2+]i was examined in dissociated rat spinal cord neurons by fura 2 microfluorimetry. The neurons investigated were choline acetyltransferase‐positive and had morphological features of motoneurons. U‐II induced [Ca2+]i increases in these neurons with a threshold of 10−9 m, and a maximal effect at 10−6 m with an estimated EC50 of 6.2 × 10−9 m. The [Ca2+]i increase induced by U‐II was mainly caused by Ca2+ influx from extracellular space, as the response was markedly attenuated in a Ca2+‐free medium. Omega‐conotoxin GVIA (10−7 m), a N‐type Ca2+ channel blocker, largely inhibited these increases, whereas the P/Q Ca2+ channel blocker, omega‐conotoxin GVIIC (10−7 m) and the l‐type Ca2+ channel blocker, verapamil (10−5 m) had minimal effects. Down‐regulation of protein kinase C by 4‐α‐phorbol 12‐myristate 13‐acetate (10−6 m) or enzyme inhibition using the specific inhibitor bisindolylmaleimide I (10−6 m) did not inhibit the observed effects. Similarly, inhibition of protein kinase G with KT5823 (10−6 m) or Rp‐8‐pCPT‐cGMPS (3 × 10−5 m) did not modify U‐II‐induced [Ca2+]i increases. In contrast, protein kinase A inhibitors KT5720 (10−6 m) and Rp‐cAMPS (3 × 10−5 m) reduced the response to 25 ± 3% and 42 ± 8%, respectively. Present results demonstrate that U‐II modulates [Ca2+]i in rat spinal cord neurons via protein kinase A cascade.