Nicotine-induced release of noradrenaline and neuropeptide Y in guinea-pig heart: role of calcium channels and protein kinase C

The role of calcium, calcium influx through calcium channels, and activation of protein kinase C for the nicotine-induced release of noradrenaline and of the sympathetic co-transmitter neuropeptide Y (NPY) was investigated in the guinea-pig isolated perfused heart. In the coronary venous overflow noradrenaline and NPY were determined by high-pressure liquid chromatography and radioimmunoassay, respectively. In the presence of extracellular calcium (1.85 mmol/l) nicotine (1-100 μmol/l) evoked a concentration-dependent overflow of both transmitters with a molar ratio of approximately 1500 (noradrenaline):1 (NPY). The nicotine-induced (100 μmol/l) overflow of noradrenaline and NPY was in a linear manner related (r = 0.79 and 0.90, respectively; p < 0.05) to the extracellular calcium concentration (0-1.85 mmol/l), and it was prevented by calcium-free perfusion. The L-type calcium channel blocker felodipine (100 nmol/l) did not affect the nicotine-induced (100 μmol/l) transmitter overflow. On the other hand, the neuronal (N-type) calcium channel blockers ω-conotoxin (100 nmol/l) and cadmium chloride (50 μmol/l) reduced the nicotine-induced (100 pmol/l) transmitter overflow to 20% of the control value, suggesting a role of N-type calcium channels in mediating the calcium influx for the nicotine-induced transmitter release. The nicotine-induced (30 μmol/l) overflow of both transmitters was two- to three-fold increased by activation of protein kinase C (phorbol 12-myristate 13-acetate; 100 nmol/l). The transmitter overflow was unaffected by 4α-phorbol 12,13-didecanoate (100 nmol/l), a phorbol ester which does not stimulate protein kinase C. Further supporting a modulatory role of protein kinase C, inhibition of the enzyme by either polymyxin B (100 gmol/I) or by cremophor RH-30 (1μmol/l) almost completely suppressed the overflow of noradrenaline and NPY. The results of the present study indicate that nicotine evokes a concentration-dependent exocytotic co-release of noradrenaline and NPY in the guinea-pig isolated perfused heart which is characterized by its dependence on extracellular calcium, calcium influx through N-type calcium channels and activation of protein kinase C.