Muscarinic Regulation of Ether-a-go-go-Related Gene K⁺ Currents in Interstitial Cells of Cajal

Abstract

The interstitial cells of Cajal (ICC) of the myenteric plexus generate a set of currents that evoke a pacemaker potential that sets the initial conditions for the contraction frequency and duration of the electrically coupled intestinal musculature. The synapse-like contacts between ICC and myenteric motor nerves highlight the potential role of the enteric nervous system in regulating the pacemaking currents in ICC. The objective of the present study was to investigate muscarinic regulation of the ether-a-go-go-related gene (ERG) K ϩ current. Immunoreactivity of the M 3 receptor (M 3 R) but not the M 2 receptor was detected on murine jejunal ICC-Auerbach's plexus (ICC-AP). The muscarinic agonist bethanechol reduced hyperpolarization-evoked peak ERG currents at Ϫ100 mV by 23 Ϯ 1% and increased both fast and slow time constants of deactivation, resulting in increased steady-state currents between Ϫ55 and Ϫ35 mV. Bethanechol also increased depolarization-evoked steady-state currents by 59 Ϯ 10% at Ϫ40 mV, whereas currents were decreased at potentials positive to 0 mV. The halfmaximal voltage of activation was shifted 11.9 mV leftward. Interestingly, the time constant of activation increased only at Ϫ40 mV. Atropine prevented and 2 M E4031 [1-[2-(6-methyl-2-pyridyl)-ethyl-4-(methylsulfonylaminobenzoyl)piperidine] inhibited bethanechol-affected currents. The effect of bethanechol was mimicked by protein kinase C (PKC) activation and diminished by PKC inhibition. Our results indicate that the ERG K ϩ channel in ICC is affected by stimulation of muscarinic receptors, probably the M 3 R, via a PKC-dependent mechanism. Modulation of the ERG K ϩ current in ICC-AP will affect the kinetics of pacemaking in the intestinal musculature.In the gastrointestinal tract, interstitial cells of Cajal associated with the myenteric plexus (ICC-AP or ICC-MP) generate a pacemaking current that is transmitted to coupled smooth muscle cells, producing an electrical slow wave that governs smooth muscle contraction (Der-Silaphet et al., 1998;Koh et al., 1998;Thomsen et al., 1998). Along the length of the intestine, there are multiple intrinsic pacemaking sites that create a stepwise gradient in frequency and, hence, transmit pacemaker-evoked slow waves toward the distal intestine, prompting anal propagation of the slow wave (Diamant and Bortoff, 1969). Without muscle excitation, slow waves do not normally bear action potentials, and little contractile activity is associated with them (Lammers and Slack, 2001). During muscle excitation, neural or otherwise, action potentials are generated by depolarized smooth muscle cells. In the circular and longitudinal muscle layers of the small intestine, the membrane potential is only sufficiently depolarized during the slow-wave plateau phase (Lammers and Slack, 2001). Because of the propagating nature of the slow waves, a peristaltic motor pattern occurs. A critically important component of peristaltic motor activity during digestion is that high-frequency pacemaker activity switches from the ...

Homeostatic Control of Sensory Output in Basal Vomeronasal Neurons: Activity-Dependent Expression ofEther-à-Go-Go-Related Gene Potassium Channels

“…mouse ERG currents (McKay and Huizinga, 2006;Yeung and Greenwood, 2007). In general, ERG1b and ERG3 deactivate much faster than ERG1a and ERG2 (Lees-Miller et al, 1997;Hirdes et al, 2005), and there are significant species variations in deact (Tseng, 2001).…”

“…During depolarization, we observed a substantial E-4031-sensitive steady-state outward current, likely attributable to activation of ERG3. This subunit shows fast activation kinetics and slow steady-state inactivation (Shi et al, 1997;McKay and Huizinga, 2006), resulting in weak inward rectification (Wimmers et al, 2002). Eleven of 27 neurons showed no drug-sensitive current (Fig.…”

hERG K+Channels: Structure, Function, and Clinical Significance

“…The acute effects of PKC activation have been examined in several different experimental systems, using either activators of PKC such as diacylglycerol (DAG)/l-oleoyl-2-acetylsn-glycerol (OAG) and phorbol 12-myristate 13-acetate (PMA) (53, 113,633) or by studying G protein-coupled receptors linked to PKC activation, including TRH receptor (213), angiotensin II receptor AT1 (676), ␣-adrenoceptors (631,671), and muscarinic receptors (113,260,407). Acute activation of PKC typically results in reduced KV11.1 current in oocytes (53, 630, 633) and HEK293 cells (113,513,676), as well as isolated guinea pig ventricular myocytes (671).…”

The Significance of Interstitial Cells in Neurogastroenterology

“…ICC express receptors for neurotransmitters such as neurokinins (NK1 and NK3 receptors), vasoactive intestinal polypeptide (VIP-1 receptors) and acetylcholine (muscarinic M 2 and M 3 receptors). 62,127,[191][192][193][194][195][196][197] Numerous studies have shown responses to NO in the GI tract depend upon the production of cyclic GMP (cGMP) by soluble guanylate cyclase. [198][199][200] Guanylate cyclase is a heterodimer comprised of 2 subunits, α and β.…”