title: Ca2+ inhibition of inositol trisphosphate-induced Ca2+ release in single smooth muscle cells of guinea-pig small intestine.
abstract: 1. Single smooth muscle cells from the longitudinal muscle layer of guinea-pig small intestine were voltage clamped using patch pipettes in the whole-cell mode. 2. When D-myo-inositol 1,4,5-trisphosphate (InsP3) was released at intervals, by photolysis of 'caged' InsP3 within the cell, increases in [Ca2+]i in many cells, as judged from Ca(2+)-activated K(+)-current, were all-or-none; release of InsP3 before a critical interval had elapsed, which was quite stable for an individual cell, resulted in no response. After Ca(2+)-induced Ca2+ release had been evoked by depolarization, the InsP3 response was inhibited. Oscillations in [Ca2+]i evoked by muscarinic receptor activation were unaffected by Ruthenium Red; during these oscillations exogenous InsP3 was not effective close to, or shortly after, peak [Ca2+]i but was effective at other times. 3. Reproducible release of Ca2+ and elevation of [Ca2+]i could be produced by brief (up to 0.5 s) pressure applications of 10 mM caffeine at intervals of 10 s or greater but caffeine itself rarely evoked oscillations in [Ca2+]i. Responses to flash release of InsP3 were reduced after caffeine-induced responses and recovery of caffeine-induced Ca2+ release was faster than recovery of InsP3-induced Ca2+ release. 4. The results support the idea that InsP3-induced Ca(2+)-store release can be inhibited by a certain level of [Ca2+]i at a time when Ca2+ stores have refilled and can be released by caffeine; they also support the suggestion that during oscillations of [Ca2+]i evoked by muscarinic receptor activation, Ca2+ inhibition of InsP3-induced Ca2+ release at some critical level of [Ca2+]i allows Ca2+ stores to refill and leads to a fall in [Ca2+]i so contributing to the oscillations which are observed.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, St George's Hospital Medical School, London, UK.
authors.forename: A V
authors.initials: AV
authors.lastname: Zholos
authors.forename: S
authors.initials: S
authors.lastname: Komori
authors.forename: H
authors.initials: H
authors.lastname: Ohashi
authors.forename: T B
authors.initials: TB
authors.lastname: Bolton
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006168:Guinea Pigs; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007421:Intestine, Small / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects
chemical_list: D007473:Ion Channels; D015221:Potassium Channels; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium