Oxytocin‐evoked repetitive rises of intracellular calcium in single cultured human myometrial cells

Repetitive transient increases in intracellular calcium were recorded in single cultured human myometrial cells exposed continuously to oxytocin (1 pM‐1 nM). Each transient was preceded by a pacemaker‐like gradual increase in baseline [Ca2+]i. Removal of extracellular Ca2+ reversibly stopped the transients although small fluctuations in [Ca2+]i were observed in seven out of eleven cells studied. In a proportion of cells (1–2%) repetitive Ca2+ transients were observed in the absence of exogenous oxytocin. The pattern of activity was similar to that seen in cells exposed to oxytocin. These spontaneous elevations in [Ca2+]i were reversibly inhibited by removing extracellular calcium. These experiments demonstrate for the first time repetitive agonist‐induced and spontaneous transient increases in [Ca2+]i in single cultured human myometrial cells.