Contribution of reverse-mode sodium-calcium exchange to contractions in failing human left ventricular myocytes

• Published in: Cardiovascular research 1998-02, Vol.37 (2), p.424-431
• Main Authors: Mattiello, J A, Margulies, K B, Jeevanandam, V, Houser, S R
• Format: Article
• Language: English
• Subjects: Calcium - metabolism; Calcium Channel Blockers - pharmacology; Calcium-Transporting ATPases - antagonists & inhibitors; Cells, Cultured; Cytosol - metabolism; Enzyme Inhibitors - pharmacology; Heart Failure - metabolism; Humans; Myocardial Contraction - drug effects; Myocardium - metabolism; Nifedipine - pharmacology; Sarcoplasmic Reticulum - metabolism; Sodium - metabolism; Sodium-Calcium Exchanger - metabolism; Thapsigargin - pharmacology
• ISSN: 0008-6363
• DOI: 10.1016/S0008-6363(97)00271-X

To examine the contribution of reverse mode sodium-calcium (Na-Ca) exchange to contractions in isolated left-ventricular myocytes from failing human heart. Low resistance patch pipettes were used to dialyze cells with Na-free or high-Na pipette solution ([Na]pipette = 0 and 20 mmol/L, respectively) to reduce or enhance Na-Ca exchange. Whole-cell membrane-potential, membrane-current and cell-shortening data were simultaneously acquired during whole-cell voltage clamp protocols. Thapsigargin (100 nmol/L) and nifedipine (1 mumol/L) were also used to inhibit sarcoplasmic reticulum (SR) Ca-ATPase and L-type Ca channels, respectively. Two types of contractions were observed. Rapid phasic contractions were seen in both Na-free and high-Na cells. Slow tonic contractions were seen only in high-Na cells. Phasic contractions demonstrated bell-shaped voltage dependence over the voltage range that corresponds to the activity of the L-type Ca channel. Although the voltage dependence of phasic contractions were similar Na-free and high-Na cells, phasic contractions in high-Na cells were larger than phasic contractions in Na-free cells. Phasic contractions were sensitive to inhibition of SR Ca-ATPase and L-type Ca channels. Tonic contractions were not inhibited by either thapsigargin or nifedipine. In thapsigargin-treated high-Na cells, tonic contraction magnitude increased exponentially with test-potential. The increases in phasic contraction magnitude observed in high-Na cells compared to Na-free cells were most likely due to increased SR Ca loading resulting from increased reverse-mode Na-Ca exchange. Our results also suggest that tonic contractions in high-Na cells were mediated by Ca entry via reverse-mode Na-Ca exchange and were not the result of either SR Ca release or L-type Ca channel activity.