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Cellular mechanism of the voltage‐dependent change in slow potentials generated in circular smooth muscle of the guinea‐pig gastric corpus
Author(s) -
Hirst G. D. S.,
Hashitani H.,
Suzuki H.
Publication year - 2008
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2008.160531
Subject(s) - depolarization , membrane potential , protonophore , biophysics , repolarization , cyclopiazonic acid , chemistry , hyperpolarization (physics) , resting potential , electrophysiology , medicine , stereochemistry , biochemistry , endoplasmic reticulum , biology , nuclear magnetic resonance spectroscopy
The cellular mechanism of the voltage‐dependent properties of slow potentials were investigated in single bundles of circular smooth muscle isolated from the gastric corpus of guinea‐pig using conventional microelectrode recordings. Hyperpolarization of the membrane by current injection decreased the frequency and increased the amplitude of slow potentials linearly. At potentials negative of −80 mV, slow potential generation was abolished and a periodic generation of clustered unitary potentials was evident. Application of cyclopiazonic acid (CPA, 20 μ m ) or thapsigargin (1 μ m ; inhibitors of Ca 2+ ‐ATPase), carbonyl cyanide m ‐chlorophenyl hydrazone (CCCP, 0.1 μ m ; mitochondrial protonophore) or 2‐aminoethoxydiphenyl borate (2‐APB, 20 μ m ; inhibitor of IP 3 receptor‐mediated Ca 2+ release) depolarized the membrane and reduced or inhibited the amplitude and frequency of slow potentials: repolarization of the membrane to the resting level by current injection resulted in a recovery of the amplitude of slow potentials in the presence of CPA or CCCP, but not 2‐APB. The slow potentials abolished by thapsigargin did not recover upon membrane repolarization. The altered frequency of slow potentials by 2‐APB, CPA or CCCP was not reversed by membrane repolarization to control potentials. Depolarization of the membrane by about 10 mV with high‐potassium solution also reduced the amplitude and increased the frequency of slow potentials in a manner restored by repolarization to control potentials upon current injection, suggesting that membrane depolarization did not affect the voltage dependency of pacemaker activity. The results indicate that in corpus circular muscles the voltage dependency of the frequency and amplitude of slow potentials requires a functional Ca 2+ store and mitochondria.