Vitamin D metabolite effects on membrane potential and potassium intracellular activity in rabbit cartilage

In rabbit cartilage growth plates, the membrane potential, Vm, and potassium intracellular activities, alpha iK, were determined in order to study the effects of long-term (48 h) and short-term (1-2 min) exposures to vitamin D metabolites. Results are as follows: (i) in proliferative cells, Vm was -55.6 +/- 0.2 mV, n = 30, and alpha ik = 50.8 +/- 4.2 mM, n = 22; (ii) in hypertrophic cells, Vm was -35.5 +/- 0.8 mV, n = 88, and alpha iK = 85.1 +/- 5.4 mM, n = 20; (iii) Vm (-44.0 +/- 1.0 mV, n = 33) and alpha iK (114.7 +/- 8.7 mM, n = 14) were increased in metatarsal hypertrophic cells incubated with 10(-10)M of 1,25(OH)2D3 but were unaffected by the presence of 24,25(OH)2D3; (iv) an hyperpolarization of Vm was observed after short-term exposure of the hypertrophic cells to 10(-10)M of 1,25(OH)2D3 (-2.2 +/- 0.2 mV, n = 34) and 24,25(OH)2D3 (-2.2 +/- 0.7 mV, n = 17) but not to 25(OH)D3 (+0.3 +/- 0.8 mV, n = 10).