title: Effects of rest interval on the release of calcium from the sarcoplasmic reticulum in isolated guinea pig ventricular myocytes.
abstract: Guinea pig cardiac myocytes were loaded with the fluorescent dye indo 1, and cell contraction was measured by a video edge-detection system. Ca2+ was released from the sarcoplasmic reticulum (SR) by rapidly cooling the myocytes or by rapid application of 10 mmol/L caffeine. Estimates of the amount of Ca2+ released from the SR after different rest intervals (ie, under different loading conditions) were obtained by measuring the current evoked by rapid application of 10 mmol/L caffeine, which we call Na+/Ca2+ exchange current. This current is completely inhibited by removal of extracellular Na+ and Ca2+ or by application of 5 mmol/L Ni2+. SR Ca2+ release after rest intervals of 5 to 120 seconds (assuming cell volume to be 30 x 10(-12) L) was estimated to be 57.8 +/- 5.7 to 25.7 +/- 4.5 mumol/L accessible cell volume, respectively, equivalent to 23 to 10 mumol/kg wet wt, respectively. There was an exponential decline in Ca2+ release from the SR after rest intervals of 2 to 120 seconds (rate constant, 0.029 s-1; t1/2, 24 seconds); thereafter, there remained a portion (56%) of Ca2+ releasable to caffeine application. We found a similar exponential decay (rate constant, 0.020 s-1; t1/2, 35 seconds) of the size of rapid cooling contractures with increasing rest intervals. The time to peak of the Na+/Ca2+ exchange current in the presence of caffeine slowed at long rest intervals, ie, at smaller SR loads. A decrease in SR load of 50% increased the time to peak of the exchange current by 213 +/- 37% (n = 6).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Cardiac Medicine, National Heart and Lung Institute, University of London, UK.
authors.forename: C M
authors.initials: CM
authors.lastname: Terracciano
authors.forename: R U
authors.initials: RU
authors.lastname: Naqvi
authors.forename: K T
authors.initials: KT
authors.lastname: MacLeod
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000494:pharmacology; D002469:Cell Separation; D003080:Cold Temperature; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D007211:Indoles; D010936:Plant Extracts / Q000494:pharmacology; D010946:Plants, Medicinal; D012146:Rest; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism; D013729:Terpenes / Q000494:pharmacology; D019284:Thapsigargin
chemical_list: D000889:Anti-Arrhythmia Agents; D005456:Fluorescent Dyes; D007211:Indoles; D010936:Plant Extracts; D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D012964:Sodium; D000252:Calcium-Transporting ATPases; C048960:indo-1; D002118:Calcium