[Effects of neuropeptide Y on ion channels in ventricular myocytes].
Neuropeptide Y (NPY) co-exists with norepinephrine (NE) in sympathetic terminals, and is the most abundant neuropeptide in myocardium. Many studies have focused on the effects of NE on ion channels in cardiac myocytes and its physiological significance has been elucidated relatively profoundly. There have been few investigations, however, on the physiological significance of NPY in myocardium. The effects of NPY on L-type Ca2+ channel currents (I(Ca-L)) were evaluated in some studies and different results were presented, which might be attributed to the different species of animal tested and different methods used. It is necessary, therefore, to study the effects of NPY on ion channels in cardiac myocytes systematically and further to discuss the biological significance of their coexistence with NE in sympathetic terminals. The single ventricular myocytes from adult rat or guinea pig (only for measuring I(K)) were prepared using enzymatic dispersion. I(Ca-L), I(to), I(Na/Ca), I(Na) and I(K) in the cellular membrane were observed using whole cell voltage-clamp recording. In the present study, NPY from 1.0 to 100 nmol/L dose-dependently inhibited I(Ca-L) (P<0.01, n=5). The maximal rate of inhibition in this study reached 39% and IC(50) was 1.86 nmol/L. NPY had no effect on the voltage-dependence of calcium current amplitude and on the voltage-dependence of the steady-state gating variables. I(Ca-L) was activated at -30 mV, reaching the maximum at 0 mV. When both NE and NPY were applied with a concentration ratio of 500:1, 10 nmol/L NPY inhibited I(Ca-L) that had been increased by 5 mumol/L NE, which was consistent with the effect of NPY only on I(Ca-L). NPY also inhibited I(Na/Ca). At a concentration of 10 nmol/L, NPY inhibited inward and outward I(Na/Ca) from (0.27+/-0.11) pA/pF and (0.45+/-0.12) pA/pF to (0.06+/-0.01) pA/pF and (0.27+/-0.09) pA/pF, respectively (P<0.05, n=4). NPY at 10 nmol/L increased I(to) from (12.5+/-0.70) pA/pF to (14.7+/-0.59) pA/pF(P<0.05, n=4). NPY at 10 nmol/L did not affect I(Na) in rat myocytes and I(K) in guinea pig myocytes. NPY increased the speed of action potential depolarization and reduced action potential duration of I(Ca-L), I(Na/Ca) and I(to), which contributed to the reduction of contraction. These results indicate that the effects of NPY are opposite to the effects of NE on ion channels of cardiac myocytes.
Zhao
Hua-Chen
HC
Department of Physiology, Shanxi Medical University, Taiyuan 030001, China.
Liu
Zhong-Bao
ZB
Feng
Qi-Long
QL
Cui
Xiang-Li
XL
Zhang
Chun-Min
CM
Wu
Bo-Wei
BW
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects*; D005260:Female; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology*; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism*; D009478:Neuropeptide Y / Q000494:pharmacology*; D009638:Norepinephrine; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors*
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D007473:Ion Channels; D009478:Neuropeptide Y; D019831:Sodium-Calcium Exchanger; D009638:Norepinephrine