Chloride-mediated junction potentials in circular muscle of the guinea pig ileum

Abstract

Junction potentials were recorded from circular muscle cells of the guinea pig ileum at various sites oral and anal to a transmural stimulus in the presence of atropine, apamin, and substance P antagonism (desensitization) at 30 degrees C. A short train of pulses produced an inhibitory junction potential (slow IJP), which preceded an excitatory junction potential (slow EJP). The slow IJP was observed up to 56.4 +/- 2.9 mm oral and 65.4 +/- 2.2 mm anal to the stimulus. The slow EJP was observed up to 50.4 +/- 1.9 mm oral and 58.3 +/- 2.1 mm anal to the stimulus. Hexamethonium (400 microM) decreased the amplitudes of the slow IJP and slow EJP at all sites. After hexamethonium, the slow IJP was observed up to 37.3 +/- 2.3 mm oral and 39.8 +/- 2.1 mm anal to the stimulus and the slow EJP was 44.2 +/- 2.5 mm oral and 43.3 +/- 2.6 mm anal to the stimulus. The slow IJP and slow EJP were associated with an increase and decrease in membrane resistance, respectively. Conditioning depolarizations of the circular muscle cells reduced the amplitudes of the slow IJP and slow EJP. Both were abolished at a membrane potential of approximately -25 mV. Conditioning hyperpolarizations increased the amplitude of both the slow IJP and slow EJP. Ionic substitution experiments with low external chloride solution (12.4 mM) resulted in an immediate increase in slow IJP and slow EJP amplitudes, whereas more prolonged perfusion resulted in a significant decrease in slow IJP and slow EJP amplitudes. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (400 microM) resulted in decreases in slow IJP and slow EJP amplitudes. These results suggest that the slow IJP and slow EJP are due to a decrease and increase in membrane chloride conductance, respectively. The noncholinergic neural pathways responsible for the slow IJP and slow EJP extend approximately 40 mm orally and anally along the longitudinal axis of the guinea pig ileum.

P2Y1 Receptors Mediate Apamin-Sensitive and -Insensitive Inhibitory Junction Potentials in Murine Colonic Circular Smooth Muscle

“…Using SK channel and nNOS inhibition, a distinctive fast IJP and slow IJP mediated by purinergic and nitrergic nerves, respectively, have been clearly shown in both guinea pig small intestine (He and Goyal, 1993) and murine lower esophageal sphincter (Zhang et al, 2008). The purinergic fast IJPs result from opening of SK channels, whereas nitrergic slow IJPs appear to be caused by closing of Ca 2ϩ -activated Cl Ϫ channels (Crist et al, 1991;Zhang and Paterson, 2003). In 1998, Spencer et al (1998a) described a non-nitrergic, apamin-resistant IJP of approximately 8 mV evoked by a single-pulse electrical stimulus in the mid to distal region of mouse colon.…”

CaMKII inhibition hyperpolarizes membrane and blocks nitrergic IJP by closing a Cl−conductance in intestinal smooth muscle

“…The resistance of the microelectrodes was between 30 and 80 M⍀ as described earlier (6,7). Intracellular recordings of membrane potential and ETP were obtained from the same smooth muscle cell using microelectrodes made from glass of 1.2-mm external diameter (Frederick Haer, Brunswick, ME) and filled with 1 M K ϩ methyl sulfate and 3 M KCl.…”

“…The details of handling of current leakage and other technical issues have been described elsewhere (6,7). Direct current, hyperpolarizing potentials of 0.5 s in duration were generated by passing current between the two stimulating plates in this bath and were monitored by a constantcurrent monitor unit (Grass Instruments CCUI) positioned in series between the plates and the stimulator.…”

“…However, the view that the nitrergic sIJP could be due to closure of Cl Ϫ conductance was not readily accepted and some leaders in the field continued to believe that nitrergic IJP was also due an increase in K ϩ conductance [see Daniel et al (8)]. On the other hand, many reports supporting the role of closure of Cl Ϫ channels have also appeared (6,10,41,43). Over the last 30 yr, many reports regarding the involvement of K ϩ currents in nitrergic IJP have appeared (19,20,40).…”

Impact of caveolin-1 knockout on NANC relaxation in circular muscles of the mouse small intestine compared with longitudinal muscles

“…These result from a direct or indirect action on K ϩ and/or Cl Ϫ channels (30,10). Several intracellular mediators, e.g., cGMP, cAMP, and intracellular calcium, have been reported to be involved in the indirect effect of NANC inhibitory neurotransmitters on K ϩ and Cl Ϫ channels (2,41,43).…”