Paracrine and Intracellular Signaling Mechanisms of Calcium Waves in Cultured Human Uterine Myocytes

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Abstract
Objective: To establish mechanisms of intercellular communication in human myometrium other than action potential propagation. Methods: Monolayer cultured human myometrium was used as a model system. The calcium-sensitive fluorescent dye, calcium green-1, was used as a probe for the concentration of intracellular free calcium. Intercellular calcium waves were initiated by mechanical stimulation and observed with video spectrofluorimetry. This technique allowed initiation of calcium waves from a known location at a known time while simultaneously controlling the flow rate of the bathing solution across the surface of the cells. Intercellular calcium waves were observed at bath flow rates between 0 and 5.1 mL/minute through a 0.4 mL chamber. Experiments were performed using low calcium, high potassium bathing solutions to eliminate the possibility of action potential signaling. Results: In still bathing solution, calcium waves radiated symmetrically from the site of initiation. With the bathing solution flowing, two mechanisms of intercellular calcium wave propagation were observed—one dependent on and one independent of the direction of bath flow. The calcium waves that were independent of bath flow used an intracellular mechanism for intercellular communication, were only observed within 100 μm of the site of wave initiation, and demonstrated mean (± standard deviation [SD]) wave speeds of 14.1 ± 2.6 μm/second. The waves dependent on bath flow used an extracellular signaling mechanism, were observed at distances much greater than 100 μm, and exhibited downstream biasing. Mean (±SD) wave speeds of flow-dependent calcium waves were faster under flow conditions than still bath conditions (36.0 ± 4.7 versus 6.2 ± 1.3 μm/second; P < .001). By exposing the cells to flurbiprofen, a water soluble prostaglandin synthetase inhibitor, both types of calcium waves were inhibited. Conclusion: Human myocytes demonstrate paracrine and intracellular signaling mechanisms for intercellular communication that are distinctly different from action potential propagation.

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