Nociceptin, Phe~1ψ-nociceptin_(1-13), nocistatin and prepronociceptin_(154-181) effects on calcium channel currents and a potassium current in rat locus coeruleus in vitro

摘要

1. The actions of the neuropeptide nociceptin, the putative nociceptin receptor antagonist [Phe1ψ(CH_2-NH)Gly~2]-nociceptin-(1-13)NH_2 (Phe~1ψ-nociceptin_(1-13)) and the putative nociceptin precursor products nocistatin (rat prepronociceptin_(125-132)) and rat prepronociceptin_(154-181) were examined on membrane properties of rat locus coeruleus (LC) neurons using whole cell patch clamp techniques. 2. Nociceptin inhibited I_(Ba) in all LC neurons, (pD_2 of 8.9, maximum inhibition 50%). The inhibition of I_(Ba) by nociceptin was associated with slowing of the activation of I_(Ba) and could be significantly reversed by a strong depolarizing prepulse. Phe~1ψ-nociceptin_(1-13) also inhibited I_(Ba) in LC neurons (notional pD_2 of 7.6, maximum inhibition 18%). Application of Phe~1ψ-nociceptin_(1-13) (1 μM) significantly occluded the subsequent effects of a co-application of nociceptin (3 nM) on I_(Ba). 3. As previously reported for nociceptin, Phe~1ψ-nociceptin_(1-13) caused an outward current in LC neurons voltage clamped at -60 mV (pD_2 of 7.1, maximum current 50% of that of methionine enkephalin, 10 μM). The Phe~1ψ-nociceptin_(1-13) induced current reversed polarity at -112 mV and exhibited pronounced inward rectification. Phe~1ψ-nociceptin_(1-13) (1 μM) reversibly inhibited the current caused by nociceptin (300 nM) by 30%. 4. Neither nocistatin nor rat prepronociceptin_(154-181) inhibited I_(Ba) in LC neurons, or prevented the subsequent inhibition by nociceptin. Neither nocistatin or prepronociceptin_(154-181) affected the membrane properties of LC neurons. 5. This study demonstrates that nociceptin modulates somatic I_(Ba) in rat LC neurons. The putative ORL1 antagonist Phe~1ψ-nociceptin_(1-13) exhibited partial agonist activity at inhibiting I_(Ba) and opening K~+ channels in LC. Other putative nociceptin precursor products were without effect on LC cells.