title: Contractile arrest increases sarcoplasmic reticulum calcium uptake and SERCA2 gene expression in cultured neonatal rat heart cells.
abstract: We developed protocols with intact cultured neonatal rat myocytes to directly evaluate the function of the sarcoplasmic reticulum (SR) Ca-ATPase (or SERCA2), Na-Ca exchange (Na-CaX), and slow Ca transport systems (mitochondria and sarcolemmal Ca-ATPase). Spontaneously beating control cells were compared with cells cultured for 2 days in the presence of verapamil (verapamil-arrested cells, VA). Intracellular calcium (Cai) transients were measured by use of indo-1 during (1) spontaneous twitches, (2) contractures induced by rapid application of caffeine (CafC, with and without Nao), and (3) twitches induced by brief depolarizations with high [K]o solution (K-twitches). We also measured mRNA levels for the SR Ca-ATPase and Na-CaX in the same experimental preparations. The t1/2 for [Ca]i decline when both the SR Ca uptake and Na-CaX were prevented was the same for control and VA cells (approximately 20 seconds), indicating unaltered slow Ca transport systems. Similarly, there was no significant difference in the t1/2 of CafC when Na-CaX was the main mechanism responsible for [Ca]i decline (t1/2 approximately 1.5 seconds), indicating unaltered Na-CaX. Conversely, we found nearly a twofold increase in the rate of [Ca]i decline during K-twitches (control t1/2, 0.84 +/- 0.05 seconds; VA t1/2, 0.48 +/- 0.06 second; P < .001), indicating an increase in SR Ca-pumping activity in VA cells. This was also reflected by a 56% increase in the peak [Ca]i reached during CafC used to assess maximal SR Ca content (427 +/- 49 nmol/L in control versus 665 +/- 75 nmol/L in VA cells).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, Loyola University School of Medicine, Maywood, Ill. 60153.
authors.forename: J W
authors.initials: JW
authors.lastname: Bassani
authors.forename: M
authors.initials: M
authors.lastname: Qi
authors.forename: A M
authors.initials: AM
authors.lastname: Samarel
authors.forename: D M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D008285:Major Histocompatibility Complex; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; D014700:Verapamil; D000252:Calcium-Transporting ATPases; D002118:Calcium