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The effects of taurine on Ca2+ uptake by the sarcoplasmic reticulum and Ca2+ sensitivity of chemically skinned rat heart.
Author(s) -
Steele D S,
Smith G L,
Miller D J
Publication year - 1990
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1990.sp017997
Subject(s) - caffeine , taurine , contracture , chemistry , endocrinology , medicine , calcium , endoplasmic reticulum , osmotic concentration , biophysics , biochemistry , biology , amino acid , surgery
1. Caffeine (10 mM) induced a transient contracture in saponin‐treated cardiac trabeculae as a result of Ca2+ release from the sarcoplasmic reticulum (SR). Regular cycles of uptake and release were repeated to stabilize responses. The SR accumulated Ca2+ during the period prior to the addition of caffeine and this was reflected in the size of the caffeine contracture. Increasing the time for Ca2+ loading between successive caffeine exposures resulted in an increase in the amplitude of the contracture. Similarly, the size of the contracture was a function of the calcium ion concentration [( Ca2+]) in the preceding loading period. 2. Taurine (microM‐40‐mM), when included in both loading and caffeine solutions, markedly potentiated the caffeine‐induced contracture. The effect occurs even if taurine was included only in the loading solutions. The potentiating effect was ascribed to a direct action of taurine on the SR, since taurine did not significantly change the [Ca2+] in the loading solutions. 3. The maximal effect of taurine was produced at approximately 5 mM; higher taurine concentrations caused a lesser potentiation of the caffeine contracture. If the solutions were balanced with respect to osmolarity the effect of taurine did not decline at high concentrations. 4. If the [Ca2+] in the loading solutions was increased to produce a caffeine‐induced contracture that peaked close to maximal Ca2(+)‐activated force, taurine caused a fall in the size of contracture and a more variable response. This result could be explained by an increase in the spontaneous release of Ca2+ from the SR in the presence of taurine. 5. In Triton‐skinned trabeculae, taurine (1 mM‐40 mM) increased the Ca2+ sensitivity of the contractile proteins in a dose‐dependent manner but had little effect on maximum Ca2(+)‐activated force. The increase in Ca2+ sensitivity was small: in a typical experiment 30 mM‐taurine reduced the [Ca2+] necessary for half‐maximal activation from 3.02 to 2.56 microM, with no significant change in the shape of the relationship.