Components of pacemaker potentials recorded from the guinea pig stomach antrum

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The effects of changes in temperature on slow waves were investigated in smooth muscle tissues isolated from the guinea-pig gastric antrum. Within the range 24°C to 42°C, elevation of temperature increased the frequency and maximum rate of rise of the upstroke phase (dV/dt) of slow waves and decreased their duration, with no alteration to amplitude or resting membrane potential. These observations also applied to follower potentials and pacemaker potentials recorded from longitudinal muscle and myenteric interstitial cells, respectively. Slow waves were comprised of 1st and 2nd components, and the latency for generating the 2nd component was decreased exponentially by elevating temperature, reaching a stable value of about 1 s above 32°C. The temperature coefficient was >2 for the frequency, dV/dt and latency of the 2nd component, about 1.7 for the duration and about 1 for amplitude. Potassium cyanide (KCN), an inhibitor of mitochondrial metabolic activity, reduced the frequency and duration of slow waves, with no alteration to other parameters (amplitude, dV/dt, latency). In the presence of 30 μM KCN, the temperature-dependency of the frequency of slow waves was diminished or abolished, while other parameters of slow waves remained unaltered. These results indicate that in slow waves the frequency may be related to metabolic activities, while the temperature-dependent changes in the dV/dt, latency for the 2nd component and duration of slow waves are produced largely by mechanisms other than metabolic activity.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Metabolic component of the temperature-sensitivity of slow waves recorded from gastric muscle of the guinea-pig

Nakamura

Kito

Hashitani

et al. 2006

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“…This conclusion was based on pharmacological tests using a Cl -channel-blocking drug (4-acetoamido-4-isothiocyanat-ostilbene-2,2-disulphonic acid; SITS). From studies of intact muscle preparations, other investigators have suggested that Ca 2+ -activated Cl -conductance is responsible for the pacemaker currents in ICCs (Hirst et al, 2002;Kito et al, 2002). These investigators have suggested that Ca 2+ released from IP3…”

Section: Possible Mechanisms For the Pacemaker Activity In Interstitimentioning

confidence: 99%

The relationship of TRP channels to the pacemaker activity of interstitial cells of Cajal in the gastrointestinal tract

Kim

2006

Interstitial cells of Cajal (ICCs) are a fundamental component of the pacemaker apparatus of the gastrointestinal (GI) tract. They have special properties that make them unique in their ability to generate and propagate slow waves in gastrointestinal smooth muscle. The pacemaker current that generates slow waves is initially due to a voltageindependent, Ca 2+ -inhibited, non-selective cationic conductance in ICC. The classical transient receptor potential (TRPC) channel 4 was suggested as a molecular candidate for the nonselective cation channel (NSCC) responsible for the pacemaker activity. We have shown that TRPC4-/-mice display normal slow waves and suggest that TRPC4 might be an essential component of the NSCC activated by muscarinic stimulation. Finally, we suggest that TRPM7 is the molecular candidate for the NSCC responsible for pacemaker activity in ICCs on the basis of electrophysiological, molecular biological, and immunohistochemical experiments.

“…In the gastric wall of laboratory animals such as the guinea-pig and mouse, many types of ICC are identified, such as those distributed within the myenteric plexus (ICC-MY), within the circular smooth muscle layers (ICC-IM) and within the submucosal plexus (ICC-SM) (Komuro et al, 1996;Burns et al, 1997). In the guinea-pig, ICC-MY generate driving potentials with initial fast transient (duration, 1-2 s) and subsequent plateau components (duration, 10-15 s), and the potentials are propagated to circular and longitudinal smooth muscle layers in an electrotonic manner through gap junctions (Dickens et al, 1999;Kito et al, 2002b). These slow waves consist of both voltage-sensitive and voltage-insensitive components (Ohba et al, 1975;Tomita, 1981), with only the former easily inhibited by caffeine (Dickens et al, 1999;Suzuki and Hirst, 1999).…”

Section: Introductionmentioning

confidence: 99%

Effects of RHC-80267, an Inhibitor of Diacylglycerol Lipase, on Excitation of Circular Smooth Muscle of the Guinea-Pig Gastric Antrum

Suzuki

Kito

Fukuta

et al. 2002

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In small segments of circular smooth muscle isolated from the guinea-pig gastric antrum, the effects of RHC-80267, an inhibitor of diacylglycerol lipase, were investigated both on regenerative slow potentials (either occurring spontaneously or as the result of a depolarizing intracellular current injection) and on the actions of acetylcholine (ACh). As diacylglycerol is a known activator of protein kinase C (PKC), it would therefore be expected that RHC-80267 would activate PKC indirectly. In circular smooth muscle bundles, spontaneously generating slow potentials recorded simultaneously from two given cells were synchronized, indicating that these two cells were electrically coupled. RHC-80267 (0.3-1 µM) increased the frequency of slow potential generation, with no alteration to the amplitude of either the slow potentials or the resting membrane potential. Synchronous electrical activity in a given pair of cells was also unchanged by RHC-80267, indicating that intercellular electrical coupling was not altered. The input resistance of smooth muscle cells calculated from the amplitude of electrotonic potentials produced by injection of current was not significantly altered by RHC-80267. The refractory period for the generation of slow potentials evoked by depolarizing stimuli was about 8 s, and it was decreased to about 5 s by RHC-80267, with no significant alteration to the amplitude of spontaneous or evoked slow potentials. ACh (0.5 µM) depolarized the membrane by about 5 mV and increased the amplitude and frequency of slow potentials. The actions of ACh on the frequency of slow potentials were enhanced by RHC-80267, with no alteration to the amplitudes of both the ACh-induced depolarization and slow potentials. These results support the idea that PKC is involved in determining the frequency of slow potentials, by shortening the refractory period for excitation of gastric smooth muscle cells.