α₂‐Adrenoceptors couple to inhibition of R‐type calcium currents in myenteric neurons

Abstract

Abstractα 2 -adrenoceptors inhibit Ca 2+ influx through voltage-gated Ca 2+ channels throughout the nervous system and Ca 2+ channel function is modulated following activation of some G-protein coupled receptors. We studied the specific Ca 2+ channel inhibited following α 2 -adrenoceptor activation in guinea pig small intestinal myenteric neurons. Ca 2+ currents (I Ca 2+ ) were studied using whole-cell patch clamp techniques. Changes in intracellular Ca 2+ (Δ[Ca 2+ ] i ) in nerve cell bodies and varicosities were studied using digital imaging where Ca 2+ influx was evoked by KCl (60 mM) depolarization. The α 2 -adrenoceptor agonist, UK 14,304 (0.01 − 1 μM) inhibited I Ca 2+ and Δ[Ca 2+ ] i ; maximum inhibition of I Ca 2+ was 40%. UK 14,304 did not affect I Ca 2+ in the presence of SNX-482 or NiCl 2 (R-type Ca 2+ channel antagonists). UK 14,304 inhibited I Ca 2+ in the presence of nifedipine, ω-agatoxin IVA or ω-conotoxin, inhibitors of L-, P/Q-and N-type Ca 2+ channels. UK 14,304 induced Inhibition of I Ca 2+ was blocked by pertussis toxin pretreatment (1 μg/ml for 2 hr). α 2 -Adrenoceptors couple to inhibition of R-type Ca 2+ channels via a pertussis toxin-sensitive pathway in myenteric neurons. R-type channels may be a target for the inhibitory actions of norepinephrine released from sympathetic nerves on to myenteric neurons. Keywordsα1E; Ca v2.3 ; calcium imaging; enteric nervous system; presynaptic inhibitionGastrointestinal motility is controlled in part by the enteric nervous system (ENS) and by extrinsic sympathetic nerves. The ENS provides primary control over gut function while the sympathetic innervation modulates ENS activity (1). The myenteric plexus, a division of the ENS, is particularly important for control of gastrointestinal motility (2). Using electrophysiological criteria, myenteric neurons can be classified as S or AH neurons (3) and AH neurons may be intrinsic primary afferent neurons (4). In AH neurons the action potential has a Ca 2+ shoulder that is dependent on activation of N-type Ca 2+ channels (5). Ca 2+ entering during the action potential triggers calcium release from intracellular stores (6,7). The rise in intracellular Ca 2+ then activates a Ca 2+ -dependent K + channel, causing a long-lasting afterhyperpolarization (AHP) (4,8,9). S neurons are interneurons and motorneurons (10). Although action potentials in S neurons are blocked completely by tetrodotoxin (sodium channel antagonist), they are also associated with increases in intracellular calcium that are partly dependent on activation of N-type Ca 2+ channels (11).Guinea pig myenteric neurons express multiple Ca2+ subtypes (12). The total Ca 2+ current (I Ca 2+ ) in myenteric neurons is composed of contributions of Ca 2+ influx through L-N-P/Q- and R-type Ca 2+ channels (13-18). The R-type channels make the largest contribution to the total I Ca 2+ in myenteric neurons of guinea-pig small intestine maintained in the primary culture (13). R-type Ca 2+ channels are composed of the pore forming α 1E subunit (19,20). SNX 482 (2...

Early Emergence of Neural Activity in the Developing Mouse Enteric Nervous System

“…In the adult ENS, N-, P/Q-, L-and R-type Ca 2ϩ currents have been recorded, mostly from guinea pig myenteric neurons (Kirchgessner and Liu, 1999;Starodub and Wood, 1999;Reis et al, 2000;Bian and Galligan, 2007 (Talavera et al, 2008). Several TRP channels are expressed in the mature ENS (Boesmans et al, 2011) and also in parts of the developing mammalian nervous system that are also of neural crest origin, including embryonic dorsal root ganglion neurons (Tamura et al, 2005;Elg et al, 2007).…”

Involvement of TRPV2 Activation in Intestinal Movement through Nitric Oxide Production in Mice

“…The method was modified from a previous report (Bian and Galligan, 2007). Male wild-type (WT) and ChATBAC-eGFP mice (5 weeks of age) were killed by cervical dislocation after light diethyl ether anesthesia.…”

Norepinephrine reduces ω-conotoxin-sensitive Ca2+ currents in renal afferent neurons in rats

“…Various subtypes of Ca 2ϩ channels are involved in this ␣ 2 -adrenoceptor-mediated process: N-type Ca 2ϩ channel inhibition has been described in intestinal submucosal neurons (48), and R-type Ca 2ϩ channel inhibition has been described in small intestinal myenteric neurons (4). The differential coupling of ␣ 2 -adrenoceptors to N-and R-type Ca 2ϩ -channels was related to differential expression of Ca 2ϩ channel subtypes in the different enteric plexi (4).…”

“…Neurons of the autonomic nervous system express multiple Ca 2ϩ channel subtypes (45), including L-, N-, P/Q-, R-and T-type channels (4,43). N-type channels were found on DRG neurons (2) as well as on peptidergic afferent nerve fibers (26,27), and these voltage-gated Ca 2ϩ channels might even be involved in the regulation of somatosensory nociceptive nerve fiber endings, which share a lot of properties with visceral afferents.…”

“…The underlying mechanism of the putative interaction between renal efferent sympathetic nerves and peptidergic afferents is as yet unknown. However, voltagegated Ca 2ϩ channels (VGCCs) are regulated by NE in neurons (4,17). VGCCs regulate intracellular calcium levels and activation of action potentials of excitable cells such as neurons or muscle cells (39).…”