Fast Ca²⁺-Induced Potentiation of Heat-Activated Ionic Currents Requires cAMP/PKA Signaling and Functional AKAP Anchoring

Abstract

Calcium influx and the resulting increase in intracellular calcium concentration ([Ca(2+)](i)) can induce enhanced sensitivity to temperature increases in nociceptive neurons. This sensitization accounts for heat hyperalgesia that is regularly observed following the activation of excitatory inward currents by pain-producing mediators. Here we show that rat sensory neurons express calcium-dependent adenylyl cyclases (AC) using RT-PCR and nonradioactive in situ hybridization. Ionomycin-induced rises in [Ca(2+)](i)-activated calcium-dependent AC and caused translocation of catalytic protein kinase A subunit. Elevation of [Ca(2+)](i) finally resulted in a significant potentiation of heat-activated currents and a drop in heat threshold. This was not prevented in the presence of suramin that nonspecifically uncouples G protein-dependent receptors. The sensitization was, however, inhibited when the specific PKA antagonist PKI(14-22) was added to the pipette solution or when PKA coupling to A kinase anchoring protein (AKAP) was disrupted with InCELLect StHt-31 uncoupling peptide. The results show that heat sensitization in nociceptive neurons can be induced by increases in [Ca(2+)](i) and requires PKA that is functionally coupled to the heat transducer, mostly likely vanilloid receptor VR-1. This calcium-dependent pathway can account for the sensitizing properties of many excitatory mediators that activate cationic membrane currents.

Inhibitor κB Kinase β Deficiency in Primary Nociceptive Neurons Increases TRP Channel Sensitivity

“…The deficiency of IKK␤ in sensory neurons of SNS-IKK␤ Ϫ/Ϫ mice may disturb the balance of these membrane events and explain the observed lower activation threshold of A␦-and C-fibers and the faster response toward mechanical and heat stimulation and enhanced nociceptive responses after capsaicin or Formalin injection. Various kinases, including protein kinase C and A, p38 mitogen-activated protein kinase, and cyclin-dependent kinase Cdk5, were reported to increase TRPV1 channel activity by phosphorylation of individual serine or threonine residues (Ji et al, 2002;Bhave et al, 2003;Distler et al, 2003;Carlton et al, 2004;Zhang et al, 2005;Siemens et al, 2006;Salazar et al, 2008), i.e., exerting opposite effects on the channel than the IKK␤-mediated negative control observed here, suggesting that IKK␤ either affects residues other than those known to increase TRPV1 activity or a mechanism not exerted by direct TRPV1 phosphorylation. The moderate increase of TRPV1 protein in IKK␤-deficient neurons, particularly at their peripheral and central terminals, suggests that IKK may also regulate the expression of TRPV1.…”

Regulation of the Benzamil-Insensitive Salt Taste Receptor by Intracellular Ca2+, Protein Kinase C, and Calcineurin

“…Unlike the case with rodents, the Bz-sensitive salt taste receptor (presumably ENaC) plays a minor role in human salt taste perception. The predominant component of human salt taste is amiloride-and Bz-insensitive (Feldman et al 2003;Ossebaard and Smith 1995). Thus the identification of the amiloride-and Bz-insensitive salt taste receptor(s), their natural and synthetic agonists, and the physiological mechanisms that regulate salt taste transduction are necessary steps in the discovery of safe and effective salt taste enhancers.…”

“…S3C), which is consistent with the observations that cAMP enhances NaCl responses by activating ENaC . Although in some studies PKA simulation has been shown to sensitize TRPV1 (Bhave et al 2002;Distler et al 2003;Mohapatra and Nau 2003;Rathee et al 2002), in other studies PKA activation did not result in an increase in TRPV1 currents (Lee et al 2000;Plant et al 2007). Our studies suggest that in TRCs TRPV1t is constitutively active and phosphorylation of the channel by PKA does not further modulate the channel activity.…”

“…ATP binds to the P 2 X 2 /P 2 X 3 receptors on the taste nerve fibers that synapse with TRCs within the taste buds (Finger et al 2005) and increase taste nerve activity.…”

Scaffolding by A-Kinase Anchoring Protein Enhances Functional Coupling between Adenylyl Cyclase and TRPV1 Channel

“…13 and 14). AKAP anchored PKA is required in this process as the Ht31 peptide (a competitor of PKA-AKAP association) blocks forskolin-and PGE 2 -induced TRPV1 sensitization in sensory neurons (15,16). AKAP79/150 is expressed in ϳ80% of TRPV1 positive DRG neurons and directly binds to TRPV1 (17)(18)(19).…”