Electrophysiological study on the physiological roles of the oscillatory release of calcium from the sarcoplasmic reticulum in myocardium.

Views: 9
Downloads: 0
このエントリーをはてなブックマークに追加

Electrophysiological study on the physiological roles of the oscillatory release of calcium from the sarcoplasmic reticulum in myocardium.

Format:
Grant
Kyushu Univ. Production Kyushu Univ. Production
Title(Other Language):
心筋筋小胞体の振動性カルシウム放出の生理的意義に関する電気生理学的研究
Responsibility:
穎原 嗣尚(九州大学・医学部・助教授)
Ehara Tsuguhisa(九州大学・医学部・助教授)
Language:
Japanese
Project Year:
1986-1987
Latest Report:
The electrical and mechanical activities related to the oscillatory release of Ca from the sarcoplasmic reticulum (SR) were studied in muscle preparations and single myocytes isolated from guinea-pig ventricles. In partially depolarized papillary muscles, rapid stimulation (1 Hz) in the presence of <beta>-adrenergic stimulants induced oscillatory afterpotentials (OAP) and aftercontractions (AC) which were produced by the oscillatory release of Ca from SR. Mg ions at concentrations of 5-12 mM were found to suppress these OAP and AC. However, Mg potentiated the twitch contractions, and this effect was due to suppression of the oscillatory release of Ca from SR during diastole. Thus, the Ca oscillation at SR appeared to decrease the amount of Ca in SR avaliable for twitch. Since microscopic Ca oscillations may be present even in normal myocardium, the above results suggest that such oscillaltions can be an important mechanism regulating the amount of Ca in SR as well as the cellular Ca homeostasis, provided there is a link between these oscillations and the Ca-extruding function of the sarcolemma. In voltage-clamped isolated myocytes, high concentrations (15-25 mM) of caffeine, which releases Ca from SR, were found to induce pulse-like small (20-30 pA at the resting potential) inward currents. These currents appeard to be activated by the intracellular Ca, since Ca injection into the cell or application of large depolarizations which produced a tonic tension enhanced them. The currents were Na-dependent but could flow in the presence of Li instead of Na. The pulse-like development suggested that the currents were generated in the membrane sites which distributed relatively scarcely in the sarcolemma. The most probable sites are those facing the juxtamembranous SR. observed currents might reflect one aspect of the functional coupling of the sarcolemma and SR. We are now further studying the nature of these currents. Another type of the Ca-activated electrical event was also noted in isolated myocytes with the patch clamp technique. This was the current through the Ca-activated non-specific cation channel, and its properties were quantiatively analyzed. This current contributes to the Ca-mediated steady background conductance and does not generate pulse-like electrical events in the whole cell level. Read more
View fulltext

Similar Items:

8
心筋細胞内カルシウム濃度調節機転 by 野間 昭典; NOMA Akinori
12
Extracellular Potassium Dependent Negative Dromotropic Action of Nicorandil in Guinea Pig Myocardium by Kuma, Fumiaki; 久間, 文明; Maruyama, Toru; 丸山, 徹; Ito, Hiroyuki; 伊東, 裕幸; Kaji, Yoshikazu; 加治, 良一; Harada, Mine; 原田, 実根
8.
心筋細胞内カルシウム濃度調節機転 by 野間 昭典; NOMA Akinori
12.
Extracellular Potassium Dependent Negative Dromotropic Action of Nicorandil in Guinea Pig Myocardium by Kuma, Fumiaki; 久間, 文明; Maruyama, Toru; 丸山, 徹; Ito, Hiroyuki; 伊東, 裕幸; Kaji, Yoshikazu; 加治, 良一; Harada, Mine; 原田, 実根