Effects of isoprenaline on cytosolic calcium concentrations and on tension in the porcine coronary artery.

Masuko Fukai, S. Abe, S. Kobayashi, J. Nishimura, H. Kanaide

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Abstract

1. Using front‐surface fluorometry and fura‐2‐loaded medial strips of the porcine coronary artery, cytosolic Ca2+ concentration ([Ca2+]i) and tension development were simultaneously monitored in an attempt to determine the mechanisms of vasorelaxation induced by l‐isoprenaline (Iso). 2. Iso actively decreased [Ca2+]i of the strips at rest, both in the presence and absence of extracellular Ca2+. 3. In the presence of extracellular Ca2+, depolarization with high‐external K+ solution induced an elevation of [Ca2+]i and tension of the rapid increase and sustained, steady‐state type; both levels depended on external K+ concentration. When Iso was applied at the time of steady state of high‐K(+)‐induced [Ca2+]i elevation, there was an initial transient reduction (the first component) followed by a subsequent sustained reduction (the second component) of [Ca2+]i. For a given [Ca2+]i level during high‐K+ depolarization, the tension developed in the presence of Iso was smaller than that in its absence. Thus, the [Ca2+]i‐tension relationship during the steady state of high‐K(+)‐induced contraction was shifted to the right by Iso. Pretreatment with ryanodine, a compound which depletes Ca2+ stored in the sarcoplasmic reticulum, abolished the first component, but not the second sustained decrease in [Ca2+]i by Iso. 4. In the presence of extracellular Ca2+ (1.25 mM), histamine (Hist) induced an abrupt (the first component) and then sustained (the second component) elevations of [Ca2+]i, while the tension rose rapidly to reach the peak, and then, gradually declined. The second, but not the first, component of [Ca2+]i elevation depended on extracellular Ca2+. Iso inhibited both the first and the second components of [Ca2+]i elevation and the contraction induced by Hist, in a concentration‐dependent manner (IC50, 2 x 10(‐8) M for the first component, and 5 x 10(‐8) M for the second component). Cumulative application of Hist (10(‐7)‐10(‐4) M) increased [Ca2+]i and tension with the [Ca2+]i‐tension relationship shifting to the left from that observed with high K+. The [Ca2+]i‐tension relationship during the Hist‐induced contraction shifted to the right by Iso. In contractions induced by a higher concentration (> or = 6 x 10(‐5) M) of Hist, despite the negligible decrease in [Ca2+]i, Iso could relax the muscle in a concentration‐dependent manner. 5. In the absence of extracellular Ca2+, Hist induced transient elevations of [Ca2+]i and tension, possibly due to a release of Ca2+ from intracellular stores, and with similar time courses to those of the first component observed in the presence of extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Original languageEnglish (US)
Pages (from-to)679-696
Number of pages18
JournalThe Journal of Physiology
Volume462
Issue number1
DOIs
StatePublished - Mar 1 1993

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Isoproterenol
Histamine
Coronary Vessels
Swine
Calcium
Myeloma Proteins
Ryanodine
Fluorometry
Sarcoplasmic Reticulum
Vasodilation
Inhibitory Concentration 50
Muscles

ASJC Scopus subject areas

  • Physiology

Cite this

Effects of isoprenaline on cytosolic calcium concentrations and on tension in the porcine coronary artery. / Fukai, Masuko; Abe, S.; Kobayashi, S.; Nishimura, J.; Kanaide, H.

In: The Journal of Physiology, Vol. 462, No. 1, 01.03.1993, p. 679-696.

Research output: Contribution to journalArticle

Fukai, Masuko ; Abe, S. ; Kobayashi, S. ; Nishimura, J. ; Kanaide, H. / Effects of isoprenaline on cytosolic calcium concentrations and on tension in the porcine coronary artery. In: The Journal of Physiology. 1993 ; Vol. 462, No. 1. pp. 679-696.
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N2 - 1. Using front‐surface fluorometry and fura‐2‐loaded medial strips of the porcine coronary artery, cytosolic Ca2+ concentration ([Ca2+]i) and tension development were simultaneously monitored in an attempt to determine the mechanisms of vasorelaxation induced by l‐isoprenaline (Iso). 2. Iso actively decreased [Ca2+]i of the strips at rest, both in the presence and absence of extracellular Ca2+. 3. In the presence of extracellular Ca2+, depolarization with high‐external K+ solution induced an elevation of [Ca2+]i and tension of the rapid increase and sustained, steady‐state type; both levels depended on external K+ concentration. When Iso was applied at the time of steady state of high‐K(+)‐induced [Ca2+]i elevation, there was an initial transient reduction (the first component) followed by a subsequent sustained reduction (the second component) of [Ca2+]i. For a given [Ca2+]i level during high‐K+ depolarization, the tension developed in the presence of Iso was smaller than that in its absence. Thus, the [Ca2+]i‐tension relationship during the steady state of high‐K(+)‐induced contraction was shifted to the right by Iso. Pretreatment with ryanodine, a compound which depletes Ca2+ stored in the sarcoplasmic reticulum, abolished the first component, but not the second sustained decrease in [Ca2+]i by Iso. 4. In the presence of extracellular Ca2+ (1.25 mM), histamine (Hist) induced an abrupt (the first component) and then sustained (the second component) elevations of [Ca2+]i, while the tension rose rapidly to reach the peak, and then, gradually declined. The second, but not the first, component of [Ca2+]i elevation depended on extracellular Ca2+. Iso inhibited both the first and the second components of [Ca2+]i elevation and the contraction induced by Hist, in a concentration‐dependent manner (IC50, 2 x 10(‐8) M for the first component, and 5 x 10(‐8) M for the second component). Cumulative application of Hist (10(‐7)‐10(‐4) M) increased [Ca2+]i and tension with the [Ca2+]i‐tension relationship shifting to the left from that observed with high K+. The [Ca2+]i‐tension relationship during the Hist‐induced contraction shifted to the right by Iso. In contractions induced by a higher concentration (> or = 6 x 10(‐5) M) of Hist, despite the negligible decrease in [Ca2+]i, Iso could relax the muscle in a concentration‐dependent manner. 5. In the absence of extracellular Ca2+, Hist induced transient elevations of [Ca2+]i and tension, possibly due to a release of Ca2+ from intracellular stores, and with similar time courses to those of the first component observed in the presence of extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

AB - 1. Using front‐surface fluorometry and fura‐2‐loaded medial strips of the porcine coronary artery, cytosolic Ca2+ concentration ([Ca2+]i) and tension development were simultaneously monitored in an attempt to determine the mechanisms of vasorelaxation induced by l‐isoprenaline (Iso). 2. Iso actively decreased [Ca2+]i of the strips at rest, both in the presence and absence of extracellular Ca2+. 3. In the presence of extracellular Ca2+, depolarization with high‐external K+ solution induced an elevation of [Ca2+]i and tension of the rapid increase and sustained, steady‐state type; both levels depended on external K+ concentration. When Iso was applied at the time of steady state of high‐K(+)‐induced [Ca2+]i elevation, there was an initial transient reduction (the first component) followed by a subsequent sustained reduction (the second component) of [Ca2+]i. For a given [Ca2+]i level during high‐K+ depolarization, the tension developed in the presence of Iso was smaller than that in its absence. Thus, the [Ca2+]i‐tension relationship during the steady state of high‐K(+)‐induced contraction was shifted to the right by Iso. Pretreatment with ryanodine, a compound which depletes Ca2+ stored in the sarcoplasmic reticulum, abolished the first component, but not the second sustained decrease in [Ca2+]i by Iso. 4. In the presence of extracellular Ca2+ (1.25 mM), histamine (Hist) induced an abrupt (the first component) and then sustained (the second component) elevations of [Ca2+]i, while the tension rose rapidly to reach the peak, and then, gradually declined. The second, but not the first, component of [Ca2+]i elevation depended on extracellular Ca2+. Iso inhibited both the first and the second components of [Ca2+]i elevation and the contraction induced by Hist, in a concentration‐dependent manner (IC50, 2 x 10(‐8) M for the first component, and 5 x 10(‐8) M for the second component). Cumulative application of Hist (10(‐7)‐10(‐4) M) increased [Ca2+]i and tension with the [Ca2+]i‐tension relationship shifting to the left from that observed with high K+. The [Ca2+]i‐tension relationship during the Hist‐induced contraction shifted to the right by Iso. In contractions induced by a higher concentration (> or = 6 x 10(‐5) M) of Hist, despite the negligible decrease in [Ca2+]i, Iso could relax the muscle in a concentration‐dependent manner. 5. In the absence of extracellular Ca2+, Hist induced transient elevations of [Ca2+]i and tension, possibly due to a release of Ca2+ from intracellular stores, and with similar time courses to those of the first component observed in the presence of extracellular Ca2+.(ABSTRACT TRUNCATED AT 400 WORDS)

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