Effects of neuropeptide Y on L‐type calcium current in guinea‐pig ventricular myocytes

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Abstract
1 Neuropeptide Y (NPY) reduces cell shortening at high concentrations in guinea-pig ventricular myocytes. We have studied the effects of the peptide on calcium current in cardiac myocytes. 2 We have recorded L-type calcium current in guinea-pig ventricular myocytes under conditions in which the effects of other overlapping currents have been minimised by using Na+-free, K+-free external solution and patch-clamp electrodes containing Cs+. 3 Peak inward calcium current is reduced by NPY at concentrations in excess of 1 nM, and maximal inhibition (31%) was found at and above concentrations of 100 nM. The IC50 value for NPY inhibition of peak calcium current was 1.72 nM. 4 NPY had no effect on the voltage-dependence of calcium current amplitude, on the time course of current inactivation, or on the voltage-dependence of the steady-state gating variables. 5 NPY did not reduce the calcium current in the presence of 8-Br-cyclic AMP, and it was also without effect when GTP-γ-S or GDP-β-S were included in the patch pipette. 6 We conclude that in guinea-pig ventricular myocytes NPY acts at low concentration to reduce L-type calcium current, via a G-protein-mediated pathway and reduction in intracellular cyclic AMP.