Relationship between force and intracellular [Ca2+] in tetanized mammalian heart muscle

David T. Yue, Eduardo Marban, W. Gil Wier

Research output: Contribution to journalArticlepeer-review

Abstract

To determine features of the steady state [Ca2+]-tension relationship in intact heart, we measured steady force and intracellular [Ca2+] ([Ca2+]i) in tetanized ferret papillary muscles. [Ca2+]i, was estimated from the luminescence emitted by muscles that had been microinjected with aequorin, a Ca2+ sensitive, bioluminescent protein. We found that by raising extracellular [Ca2+] and/or by exposing muscles to the Ca2+ channel agonist Bay K 8644, tension development could be varied from rest to an apparently saturating level, at which increases in [Ca2+]i produced no further rise in force. 95% of maximal Ca2+-activated force was reached at a [Ca2+]i of 0.85 ± 0.06 µM (mean ± SEM; n = 7), which suggests that the sensitivity of the myofilaments to [Ca2+]i is far greater than anticipated from studies of skinned heart preparations (or from previous studies using Ca2+-sensitive microelectrodes in intact heart). Our finding that maximal force was reached by - µM also allowed us to calculate that the steady state [Ca2+]i-tension relationship, as it might be observed in intact muscle, should be steep (Hill coefficient of >4), which is consistent with the Hill coefficient estimated from the entire [Ca2+]itension relationship derived from families of variably activated tetani (6.08 ± 0.68; n = 7). Finally, with regard to whether steady state measurements can be applied directly toward understanding physiological contractions, we found that the relation between steady force and [Ca2+]i obtained during tetani was steeper than that between peak force and peak [Ca2+]i observed during physiological twitches.

Original languageEnglish (US)
Pages (from-to)223-242
Number of pages20
JournalJournal of General Physiology
Volume87
Issue number2
DOIs
StatePublished - Feb 1 1986

ASJC Scopus subject areas

  • Physiology

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