L-type calcium-channel activity of cultured human parathyroid cells is proportional to calcium concentration of the cell-culture medium

Abstract

We have previously shown that L-type Ca²⁺ channels provide a pathway for extracellular Ca²⁺ entry in cultured parathyroid cells from patients with secondary hyperparathyroidism. Because the cells previously examined were cultured in a standard DMEM, the ionized Ca²⁺ concentration (approximately 1.8 mM) is higher than that of our plasma (around 1.2 mM). We therefore asked whether the cells exhibit L-type Ca²⁺-channel activity when cultured in a medium containing Ca²⁺ of lower than 1.2 mM. The parathyroid cells were plated on a gelatin-coated thin cover glass and cultured in a medium containing Ca²⁺ of either 0.9, 1.2, or 1.8 mM. Two-days after starting cell culture, the cells, loaded with fluo-4 AM, were challenged to 150 mM K⁺ solution containing 1.5 mM Ca²⁺. Fluo-4 fluorescence was detected with a Nipkow-type confocal microscopy system. About 70% of the cells, cultured in 1.8 mM Ca²⁺, responded to the high K⁺ solution, exhibiting large fluo-4 Ca²⁺ transients. However, about 30% of the cells cultured in 0.9 mM Ca²⁺ responded to the high-K⁺ solution, showing the smaller amplitude of Ca²⁺ transients. The cells cultured in 1.2 mM Ca²⁺ appeared to show intermediate response. Thus, L-type Ca²⁺ channels may well be involved in the regulation of parathyroid hormone secretion under hypercalcemic and possibly normal conditions. [J Physiol Sci. 2007;57 Suppl:S79]