Abstract 494: Differences in Sarcoplasmic Reticulum Ca 2+ Loading and Spontaneous Ca 2+ Release in Permeabilized Sinoatrial Nodal and Ventricular Myocytes: Effect of cAMP
| Autor: | Syevda G. Sirenko, Alexey E. Lyashkov, Dongmei Yang, Edward G. Lakatta, Tatiana M. Vinogradova |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | Circulation. 116 |
| ISSN: | 1524-4539 0009-7322 |
| Popis: | To maintain their normal automaticity, sinoatrial nodal cells (SANC) have a unique property to generate spontaneous, local Ca 2+ release (LCR) from sarcoplasmic reticulum (SR) under physiological conditions. To further characterize the mechanisms that underlie LCR’s, we compared SR Ca 2+ loading and release in saponin permeabilized, rabbit SANC and ventricular myocytes (VM) over a wide range of free [Ca 2+ ] in a physiological buffer containing 0.5 mM EGTA. The SR Ca 2+ load, indexed as Ca 2+ released by a rapid application of caffeine, was assessed by a confocal linescan image as the amplitude of Fluo-4 of Ca 2+ fluorescent transient (F/F 0 ); total spontaneous LCR signal mass during a 400 ms period over 100 μm was assessed by integrating the fluorescence of each LCR and summating the integral of all LCR’s. Over a range of free [Ca 2+ ] from 50 to 200 nM SR Ca 2+ load was the same in two cell types (Fig. A ), but at 250 nM SR load it doubled in VM, but not in SANC. Failure of SANC SR load to further increase may be attributed to the exaggerated spontaneous LCR: at 200 nM free Ca 2+ , spontaneous LCR signal mass was 4-times greater in SANC than in VM. A greater LCR signal mass in SANC than in VM at an equal or lesser SR Ca 2+ load indicates that spontaneous Ca 2+ release mechanisms differ in 2 cell types, possibly, on the basis of a recent report of high basal levels of cAMP/PKA phosphorylation in SANC. When VM were exposed to cAMP (10 μM) spontaneous LCR signal mass markedly increased (Fig. B ) at a constant Ca 2+ load (150 nM [Ca 2+ ]i Fig. A ). Thus, in physiological [Ca 2+ ], spontaneous LCR’s differ in SANC vs VM, and this may be explained, in part at least, by high basal cAMP/PKA phosphorylation of Ca 2+ cycling proteins in SANC. |
| Databáze: | OpenAIRE |
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