Neuropeptide Y Is an Essential In Vivo Developmental Regulator of Cardiac I Ca,L

Abstract

Cell culture studies demonstrate an increase in cardiac L-type Ca 2+ current ( I Ca,L ) density on sympathetic innervation in vitro and suggest the effect depends on neurally released neuropeptide Y (NPY). To determine if a similar mechanism contributes to the postnatal increase in I Ca,L in vivo, we prepared isolated ventricular myocytes from neonatal and adult mice with targeted deletion of the NPY gene ( Npy −/− ) and matched controls ( Npy +/+ ). Whole-cell voltage clamp demonstrates I Ca,L density increases postnatally in Npy +/+ (by 56%), but is unchanged in Npy −/− . Both I Ca,L density and action potential duration are significantly greater in adult Npy +/+ than Npy −/− myocytes, whereas I Ca,L density is equivalent in neonatal Npy +/+ and Npy −/− myocytes. These data indicate NPY does not influence I Ca,L prenatally, but the postnatal increase in I Ca,L density is entirely NPY-dependent. In contrast, there is a similar postnatal negative voltage shift in the I -V relation in Npy +/+ and Npy −/− , indicating NPY does not influence the developmental change in I Ca,L voltage-dependence. Immunoblot analyses and measurements of maximally activated I Ca,L (in presence of forskolin or BayK 8644) show that the differences in current density between Npy +/+ and Npy −/− cannot be attributed to altered Ca 2+ channel α 1C subunit protein expression. Rather, these results suggest that the in vivo NPY-dependent postnatal increase in I Ca,L density in cardiac myocytes results from regulation I Ca,L properties by NPY.