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Sympathetic innervation alters activation of pacemaker current ( I f ) in rat ventricle
Author(s) -
Qu Jihong,
Cohen Ira S.,
Robinson Richard B.
Publication year - 2000
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2000.t01-1-00561.x
Subject(s) - medicine , endocrinology , neuropeptide y receptor , myocyte , ventricle , prazosin , antagonist , agonist , chemistry , sympathetic innervation , adrenergic , biology , receptor , neuropeptide
1 Pacemaker current ( I f ) exists in both neonatal and adult ventricles, but activates at more negative voltages in the adult. This study uses whole‐cell patch clamp to investigate the factors that may contribute to the maturational shift of I f , comparing neonatal rat ventricular myocytes that were cultured for 4‐6 days either alone, in co‐culture with sympathetic nerves, or with neurotransmitters chronically present in culture. 2 If recorded from nerve‐muscle co‐cultures had a significantly more negative and shallower activation‐voltage relation than that from control muscle cultures, which was reflected in the midpoint potential ( V 50 ) and slope factor ( K ) of activation. This effect of innervation was prevented by the sustained presence in the culture of the α 1 ‐adrenergic antagonist prazosin (Pz) at 10 −7 M. 3 In parallel experiments, myocytes treated with noradrenaline (NA) at 10 −7 M or neuropeptide Y (NPY) at 10 −7 M during culture had the same I f activation as control cells, but cells treated with NA and NPY together had a significantly more negative and shallower activation curve. Maximum conductance and reversal potential were unchanged. 4 The effect of chronic exposure to NA + NPY was prevented by the sustained presence of either Pz or the NPY Y 2 selective antagonist T 4 ‐[NPY(33‐36)] 4 (3.5 × 10 −7 M) in the culture, indicating a requirement for both α 1 ‐adrenergic and NPY Y 2 activation. 5 Substituting NA with the α 1A ‐adrenergic selective agonist A61603 (5‐10 × 10 −9 M), in the presence of NPY, did not alter I f , suggesting the involvement of α 1B ‐ rather than α 1A ‐adrenoceptors. Further, sequential exposure to NPY followed by NA was effective in reproducing the action of chronic simultaneous exposure to these agonists, but sequential exposure to NA followed by NPY was ineffective. 6 The results are consistent with past studies indicating that NPY affects the functional expression of the α 1B ‐adrenergic cascade and suggest that sympathetic innervation induces a negative shift of I f in ventricle via a combined action at α 1B ‐adrenergic and NPY Y 2 receptors. This effect of innervation probably contributes to the developmental maturation of I f activation.