The mechanism of propagation of intracellular calcium waves in cultured human uterine myocytes

OBJECTIVE: The primary goal of this work was to determine the relative impo rtance of sarcoplasmic reticulum inositol 1,4,5-triphosphate receptors and ryanodine receptors in the mechanism of intracellular calcium wave propagat ion in human uterine myocytes. A secondary goal was to identify the rate-de termining step of calcium wave propagation. STUDY DESIGN: Pregnant human myometrium was obtained at the time of cesarea n delivery, enzymatically dispersed, and cultured through several passages. Intracellular calcium wave velocities were measured with video fluorescenc e microscopy and the calcium-dependent fluorescent dye calcium green 1. Exp erimental conditions were modified by exposure of the cells to ruthenium re d (blocked ryanodine receptor), ryanodine (locked open ryanodine receptor), oxytocin (increased inositol-l,4,5-triphosphate), sodium butyrate (intrace llular acidification), ammonium chloride (intracellular alkalinization), an d elevation of temperature (from 19 degreesC to 30 degreesC). RESULTS: Wave velocities were found to be the same for spontaneously occurr ing (9.6 +/- 2.6 mum/s) and oxytocin-stimulated (10.3 +/- 3.4 mum/s) waves. Advance treatment of the cells with ryanodine or ruthenium Fed failed to c hange oxytocin-stimulated wave velocities from control values. The temperat ure dependence of calcium wave velocities was studied across the range 19 d egreesC to 30 degreesC. Plots of wave velocities versus the inverse of the temperature yielded apparent activation energies that were the same for spo ntaneous (13.2 +/- 0.3 kcal/mol) and oxytocin-induced (14.3 +/- 1.6 kcal/mo l) waves. After intracellular acidification by treatment with butyrate (20 mmol/L) wave velocities increased by 44%. Wave velocities decreased by 35% after treatment with ammonium chloride (20 mmol/L). CONCLUSION: Propagation of intracellular calcium waves in cultured human ut erine myocytes exhibited mechanisms of sarcoplasmic reticulum calcium relea se that could use either inositol 1,4,5-triphosphate receptors alone or rya nodine receptors alone, or both together. The rate-determining step for cal cium wave propagation was diffusion of calcium though a highly buffered cyt oplasm.