Abstract
Summary
Norepinephrine (NE) induced either phasic or tonic contractions in isolated rings of cat mesenteric arteries. Tetraethylammonium (TEA), 0.6-120 mM enhanced the peak contractile response to NE but reduced the steady-state response. Manganese, 0.06-0.12 mM, inhibited the peak NE response with no effect on steady-state force development. TEA-potentiation was maximal at 2-20 mM. No potentiation occurred in calcium-free solutions or when the vessel was depolarized by high external potassium concentrations. These observations provide circumstantial evidence that mesenteric vasoconstriction may be associated with “calcium-spike” activity and that vasoconstrictor escape may be due to fading of this activity.
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