Intracellular free calcium concentration/force relationship in rabbit inferior vena cava activated by norepinephrine and high K+.
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 alpha-adrenergic agonist norepinephrine (10 microM) 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+.
Khalil
R A
RA
Department of Pharmacology, University of Miami School of Medicine, FL 33136.
van Breemen
C
C
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D016257:Fura-2; D007537:Isometric Contraction / Q000187:drug effects* / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology*; D011188:Potassium / Q000494:pharmacology*; D011817:Rabbits; D014682:Vena Cava, Inferior / Q000187:drug effects / Q000502:physiology*
D011188:Potassium; D002118:Calcium; D016257:Fura-2; D009638:Norepinephrine