Abstract
The relationship between isometric tension and free cytoplasmic calcium, [Ca2+]i, was investigated in rat isolated resistance arteries using fura-2. Depolarisation with 125 mM K+ induced a tonic contraction, while [Ca2+]i increased transiently but stabilised above resting [Ca2+]i. Furthermore, the tension/[Ca2+]i ratio was lower during activation with 125 mM K+ if the effect of endogenous noradrenaline (NA) was inhibited. Concentration/ response curves with NA and K+ indicated that NA increased the sensitivity to [Ca2+]i. Calcium concentration/response curves in the presence of 10 μM NA or 125 mM K+ showed that NA could induce force at or below resting [Ca2+]i, while for any given bath calcium concentration, [Ca2+]i was similar in the presence of NA or K+. Addition of NA or vasopressin (AVP) to vessels depolarised with 125 mM K+ caused force development but no increase in [Ca2+]i, suggesting that agonists increase the efficacy of [Ca2+]i. However, during activation with AVP the efficacy of [Ca2+]i decreased time-dependently. The results suggest that in resistance arteries [Ca2+]i plays a crucial role in excitation-contraction coupling, but the tension/[Ca2+]i relationship can be modified by exogenous and endogenous agonists.
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Jensen, P.E., Mulvany, M.J. & Aalkjaer, C. Endogenous and exogenous agonist-induced changes in the coupling between [Ca2+]i and force in rat resistance arteries. Pflugers Arch. 420, 536–543 (1992). https://doi.org/10.1007/BF00374630
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DOI: https://doi.org/10.1007/BF00374630