부산대학교 도서관

The ability to fight or flee from a threat relies on an acute adrenergic surge that augments cardiac output, which is dependent on increased cardiac contractility and heart rate. This cardiac response depends on [beta]-adrenergic-initiated reversal of the small RGK G protein Rad-mediated inhibition of voltage-gated calcium channels ([Ca.sub.v]) acting through the [Ca.sub.v][beta] subunit. Here, we investigate how Rad couples phosphorylation to augmented [Ca.sup.2+] influx and increased cardiac contraction. We show that reversal required phosphorylation of [Ser.sup.272] and [Ser.sup.300] within Rad's polybasic, hydrophobic C- terminal domain (CTD). Phosphorylation of [Ser.sup.25] and [Ser.sup.38] in Rad's N-terminal domain (NTD) alone was ineffective. Phosphorylation of [Ser.sup.272] and [Ser.sup.300] or the addition of 4 Asp residues to the CTD reduced Rad's association with the negatively charged, cytoplasmic plasmalemmal surface and with [Ca.sub.v][beta], even in the absence of [Ca.sub.v][alpha], measured here by FRET. Addition of a posttranslationally prenylated CAAX motif to Rad's C-terminus, which constitutively tethers Rad to the membrane, prevented the physiological and biochemical effects of both phosphorylation and Asp substitution. Thus, dissociation of Rad from the sarcolemma, and consequently from [Ca.sub.v][beta], is sufficient for sympathetic upregulation of [Ca.sup.2+] currents.
Introduction Calcium influx through voltage-gated L-type [Ca.sup.2+] channels ([Ca.sub.v]1.2) is an essential link in the chain of signals that trigger the contraction of every heartbeat. Norepinephrine released from sympathetic neurons [...]