Effects of calcium on frequency-modulated secretion of vasopressin from isolated murine neural lobes.

The relationship between external calcium and frequency-facilitated arginine vasopressin (AVP) secretion from the murine neurointermediate lobe was examined in vitro. We evaluated the calcium-dependency of frequency-dependent release in this system, and found that log AVP secretion versus log external calcium plots gave slopes of 0.71, 0.92 and 1.2 for 5, 10 and 20 Hz stimulation, respectively. These slopes are considerably lower than the slopes of 3-4 Hz found at conventional synaptic junctions.