Redistribution of intracellular Ca2+ stores after β-adrenergic stimulation of rat tail artery SMC

Yoshiyuki Miyashita, Steven J. Sollott, Linda Cheng, James L. Kinsella, Eio Koh, Edward Lakatta, Jeffrey P. Froehlich

Research output: Contribution to journalArticle

Abstract

β-Adrenergic agonists induce the relaxation of vascular smooth muscle by a mechanism that activates the extrusion of Na+ and Ca2+ from the cell. A primary source of contractile Ca2+ resides in the sarcoplasmic reticulum (SR), which releases Ca2+ in response to vasoactive agents through inositol trisphosphate-mediated channels. To determine if smooth muscle relaxation induced by β2-adrenergic agonists involves the redistribution of intracellular Ca2+, we studied the effects of isoproterenol (Iso) on freshly isolated, single rat tail artery smooth muscle cells loaded with fura 2, using digital ratiometric fluorescence imaging. Stimulation with 1 μM phenylephrine (PE) or norepinephrine produced phasic and tonic increases in cytoplasmic intracellular Ca2+ concentration ([Ca2+]i) associated with cell shortening. Exposure to caffeine and to Ca2+-free solutions eliminated the phasic and tonic components, respectively, from the Ca2+ signal. Intermittent superfusion with PE or caffeine was used to evaluate SR Ca2+ stores after stimulation by Iso. Exposure to 1 μM Iso induced a time-dependent decrease in PE-activated peak and tonic [Ca2+]i without any change in resting [Ca2+]i. Intermittent stimulation with 10 mM caffeine revealed a similar decline in peak [Ca2+]i, indicating Iso-dependent depletion of SR Ca2+ stores. The Ca2+ that remained in the SR after prolonged exposure to Iso (30% of the pre-Iso level by 80 min at 22°C) failed to elicit a contractile response. The cells, perfused with a Na+- and Ca2+-free medium to block Na+/ Ca2+ exchange, prevented depletion of the SR Ca2+ stores by Iso. We propose that Iso inhibits agonist-mediated Ca2+ influx through sarcolemmal Ca2+ channels and activates Ca2+ redistribution from storage sites in the SR to the extracellular compartment by a mechanism that involves Na+/Ca2+ exchange. These combined effects of Iso facilitate smooth muscle relaxation (and reduce vascular tonus) by reducing the increase in cytoplasmic Ca2+ evoked by vasoconstrictors.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Volume41
Issue number1
StatePublished - Jan 1997
Externally publishedYes

Fingerprint

Isoproterenol
Adrenergic Agents
Tail
Arteries
Sarcoplasmic Reticulum
Phenylephrine
Caffeine
Adrenergic Agonists
Muscle Relaxation
Smooth Muscle
Fura-2
Optical Imaging
Vasoconstrictor Agents
Inositol
Vascular Smooth Muscle
Smooth Muscle Myocytes
Blood Vessels
Norepinephrine

Keywords

  • β-Adrenergic relaxation
  • Arterial smooth muscle
  • Fura 2
  • Intracellular calcium
  • Isoproterenol
  • Sarcoplasmic reticulum

ASJC Scopus subject areas

  • Physiology

Cite this

Redistribution of intracellular Ca2+ stores after β-adrenergic stimulation of rat tail artery SMC. / Miyashita, Yoshiyuki; Sollott, Steven J.; Cheng, Linda; Kinsella, James L.; Koh, Eio; Lakatta, Edward; Froehlich, Jeffrey P.

In: American Journal of Physiology - Heart and Circulatory Physiology, Vol. 41, No. 1, 01.1997.

Research output: Contribution to journalArticle

Miyashita, Yoshiyuki ; Sollott, Steven J. ; Cheng, Linda ; Kinsella, James L. ; Koh, Eio ; Lakatta, Edward ; Froehlich, Jeffrey P. / Redistribution of intracellular Ca2+ stores after β-adrenergic stimulation of rat tail artery SMC. In: American Journal of Physiology - Heart and Circulatory Physiology. 1997 ; Vol. 41, No. 1.
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AU - Koh, Eio

AU - Lakatta, Edward

AU - Froehlich, Jeffrey P.

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AB - β-Adrenergic agonists induce the relaxation of vascular smooth muscle by a mechanism that activates the extrusion of Na+ and Ca2+ from the cell. A primary source of contractile Ca2+ resides in the sarcoplasmic reticulum (SR), which releases Ca2+ in response to vasoactive agents through inositol trisphosphate-mediated channels. To determine if smooth muscle relaxation induced by β2-adrenergic agonists involves the redistribution of intracellular Ca2+, we studied the effects of isoproterenol (Iso) on freshly isolated, single rat tail artery smooth muscle cells loaded with fura 2, using digital ratiometric fluorescence imaging. Stimulation with 1 μM phenylephrine (PE) or norepinephrine produced phasic and tonic increases in cytoplasmic intracellular Ca2+ concentration ([Ca2+]i) associated with cell shortening. Exposure to caffeine and to Ca2+-free solutions eliminated the phasic and tonic components, respectively, from the Ca2+ signal. Intermittent superfusion with PE or caffeine was used to evaluate SR Ca2+ stores after stimulation by Iso. Exposure to 1 μM Iso induced a time-dependent decrease in PE-activated peak and tonic [Ca2+]i without any change in resting [Ca2+]i. Intermittent stimulation with 10 mM caffeine revealed a similar decline in peak [Ca2+]i, indicating Iso-dependent depletion of SR Ca2+ stores. The Ca2+ that remained in the SR after prolonged exposure to Iso (30% of the pre-Iso level by 80 min at 22°C) failed to elicit a contractile response. The cells, perfused with a Na+- and Ca2+-free medium to block Na+/ Ca2+ exchange, prevented depletion of the SR Ca2+ stores by Iso. We propose that Iso inhibits agonist-mediated Ca2+ influx through sarcolemmal Ca2+ channels and activates Ca2+ redistribution from storage sites in the SR to the extracellular compartment by a mechanism that involves Na+/Ca2+ exchange. These combined effects of Iso facilitate smooth muscle relaxation (and reduce vascular tonus) by reducing the increase in cytoplasmic Ca2+ evoked by vasoconstrictors.

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