Contractile arrest increases sarcoplasmic reticulum calcium uptake and SERCA2 gene expression in cultured neonatal rat heart cells

José W M Bassani, Ming Qi, Allen M. Samarel, Donald M Bers

Research output: Contribution to journalArticle

35 Scopus citations

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 heating control cells were compared with cells cultured for 2 days in the presence of verapamil (verapamil-arrested cells VA). Intracellular calcium (Ca(i)) transients were measured by use of indo-1 during (1) spontaneous twitches, (2) contractures induced by rapid application of caffeine (CafC, with and without Na(o)), 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 t( 1/2 ) for [Ca](i) decline when both the SR Ca uptake and Na-CaX were prevented was the same for control and VA cells (≃20 seconds), indicating unaltered slow Ca transport systems. Similarly, there was no significant difference in the t( 1/2 ) of CafC when Na- CaX was the main mechanism responsible for [Ca](i) decline (t( 1/2 )≃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 t( 1/2 ), 0.84±0.05 seconds; VA t( 1/2 ), 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). In agreement with these functional effects, we found no change in Na-CaX mRNA levels but a marked upregulation of both the SERCA2 mRNA and protein levels in VA cells (to 166±10% and 164±20%, respectively). Thus, verapamil arrest induced an increase in SR Ca uptake (and SERCA2 expression) without affecting the Na-CaX activity (or expression) or the slow Ca transport systems.

Original languageEnglish (US)
Pages (from-to)991-997
Number of pages7
JournalCirculation Research
Volume74
Issue number5
StatePublished - May 1994
Externally publishedYes

Keywords

  • Ca(i) transients
  • caffeine
  • hypertrophy
  • Na-Ca exchange
  • rat
  • SR Ca-ATPase

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine

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