Intracellular free calcium concentration / force relationship in rabbit inferior vena cava activated by norepinephrine and high K+
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- Khalil, R.A. & van Breemen, C. Pflügers Arch (1990) 416: 727. doi:10.1007/BF00370622
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The changes in isometric force and the underlying fluctuations in intracellular free calcium concentration ([Ca2+]i) were monitored simultaneously in thin sheets of rabbit inferior vena cava loaded with the fluorescent Ca2+ indicator fura-2. In resting tissues bathed in physiological saline solution, the estimated [Ca2+]i was approximately 105 nM. The α-adrenergic agonist norepinephrine (10 μM) caused an initial rise in [Ca2+]i to 264 nM during force development, which dropped to 216 nM during force maintenance. The maintained norepinephrine-induced increase in force and [Ca2+]i was reversed in Ca2+-free (2 mM EGTA) solution. Membrane depolarization by high K+ (80 mM) significantly increased [Ca2+]i to 234 nM. Compared to norepinephrine, high K+ caused about the same steady-state increase in [Ca2+]i, but a smaller increase in force. [Ca2+]i/force curves were constructed at different concentrations of extracellular Ca2+, with either norepinephrine or high K+ as a stimulant. The curve generated with norepinephrine was located to the left of that generated with high K+.