Volume-activated chloride currents in interstitial cells of Cajal

Abstract

cells of Cajal (ICC) undergo marked morphological changes on contraction of the musculature, making it essential to understand properties of mechanosensitive ion channels. The whole cell patch-clamp technique was used to identify and to characterize volume-activated Cl Ϫ currents in ICC cultured through the explant technique. Hypotonic solutions (Ϸ210 mosM) activated an outwardly rectifying current, which reversed near the equilibrium potential for Cl Ϫ . Time-dependent inactivation occurred only at pulse potentials of ϩ80 mV, with a time constant of 478 Ϯ 182 ms. The degree of outward rectification was calculated using a rectification index, the ratio between the slope conductances of ϩ65 and Ϫ55 mV, which was 13.9 Ϯ 1.5 at 76 mM initial extracellular Cl Ϫ concentration. The sequence of relative anion permeability of the outwardly rectifying Cl Ϫ channel wasThe chloride channel blockers, DIDS and 5-nitro-2-(3-phenlypropl-amino)benzoic acid, caused a voltage-dependent block of the outwardly rectifying Cl Ϫ current, inhibition occurring primarily at depolarized potentials. On exposure to hypotonic solution, the slope conductance significantly increased at the resting membrane potential (Ϫ70 mV) from 1.2 Ϯ 0.2 to 2.0 Ϯ 0.4 nS and at the slow-wave plateau potential (Ϫ35 mV) from 2.1 Ϯ 0.3 to 5.0 Ϯ 1.0 nS. The current was constitutively active in ICC and contributed to the resting membrane potential and excitability at the slow-wave plateau. In conclusion, swelling or volume change will depolarize ICC through activation of outwardly rectifying chloride channels, thereby increasing cell excitability. gut motility; intestinal peristalsis; distension; pacemaker cells INTERSTITIAL CELLS OF CAJAL (ICC) are c-kit-positive interstitial cells within the gut musculature, connected to smooth muscle cells by gap junctions and to enteric nerve varicosities by special synapselike junctions (27). These features are common to most ICC subtypes in most species despite the fact that the dominant function of the ICC subtypes might differ. A single ICC may be connected to 10 or more smooth muscle cells (21). Hence, muscle cell contraction and relaxation will affect ICC. Indeed, in a recent study, dramatic structural changes were shown to occur in ICC in the mouse small intestine on distension (28). Before these studies, based primarily on structural information, it was already hypothesized that ICC might be stretch receptors conveying information about contractility and stretch of the musculature to smooth muscle cells and enteric nerves (4,22). To understand the physiological basis of ICC responding to the changing contractile state of the gut musculature, it is necessary to understand the characteristics and eventually the role of volume-activated ion channels in ICC. Therefore, the objective of the present study was to identify and characterize ion channels that were responsive to volume changes (cell swelling). In the present experiments, we used a patch-clamp technique to test this hypothesis and found that ICC generate volume-ac...

Volume-activated chloride channels in mice Leydig cells

“…Nevertheless, they show some common features such as the dependence on intracellular ATP, outward rectification, time-dependent inactivation at positive potentials, and the fact that I − is more permeable than Cl − [28]. Although poorly selective, a wide range of compounds can block I Cl,swell at micromolar concentrations including: calyx-arenes, glibenclamide, tamoxifen, 4-acetamido−4′-isothiocyanostilbene-2,2′-disulphonic acid (SITS), 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS), 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), anthracene-9-carboxylic acid (9-AC), niflumic acid, and purinergic antagonists [1,16,24,35,41,47]. I Cl,swell can also be modulated by PKA, PKC, PKT, and MAP kinases, depending on the cell type and experimental conditions [9,46,53].…”

A novel exon in the human Ca2+-activated Cl− channel Ano1 imparts greater sensitivity to intracellular Ca2+

“…For several years, Ca 2ϩ -activated Cl Ϫ currents have been recorded from interstitial cells of Cajal (ICCs) (12,13,16,24,25,47,48). In particular, anoctamin 1 (Ano1), also known as TMEM16A or DOG1, is a selective marker of ICCs in the GI tract (9).…”

Characteristics of Gintonin-Mediated Membrane Depolarization of Pacemaker Activity in Cultured Interstitial Cells of Cajal

“…On the other hand, ICC pacemaker activities are mainly due to periodic activations of non-selective cation channels (NSCCs) [15,16] or Cl - channels [17,18,19,20,21,22], and TRPM7 and ANO1 channels are the main candidates for the NSCC and Cl - channels responsible for the pacemaker activity in ICC [18,25,26,30]. Therefore, TRPM7 and ANO1 modulators are potential targets for the treatment of GI motility disorders.…”

“…In addition, evidence indicates that endogenous agents, such as, neurotransmitters, hormones, and paracrine substances, modulate GI tract motility by influencing ICC [14]. It has been shown that the pacemaker activities of ICC in the murine small intestine are mainly due to periodic activations of nonselective cation channels (NSCCs) [15,16] or Cl - channels [17,18,19,20,21,22]. Kim et al [16] suggested that transient receptor potential melastatin (TRPM) 7 is required for ICC pacemaker activity in the murine small intestine, and a Ca 2+ -activated Cl - channel (CaCC) is involved in slow wave generation in ICC.…”

“…Tmem16A encodes the anoctamin 1 (ANO1) channel, which is expressed in human embryonic kidney (HEK)-293 cells [18,23,24,25,26]. Additionally, other research groups have suggested that inwardly rectifying Cl - channels [19], volume-activated chloride channels [20], a high-conductance chloride channel (which was renamed to the maxi-channel) [21,22], ether-a-go-go-related gene (ERG) potassium channels [27], nonselective cation channels [28] and voltage dependent Ca 2+ channels [29] play prominent roles in determining pacemaker activity in the gut. However, the role of Tmem16A in pacemaker activity in ICC was identified in TMEM16A knockout mice [30], and many papers have suggested that Tmem16A participates in pacemaker activity [25,26,30].…”