Detection of L-type calcium channel activity in human normal parathyroid cells

Abstract

We have previously shown that voltage-dependent L-type Ca²⁺ channels provide a pathway for extracellular Ca²⁺ entry in cultured parathyroid cells isolated from patients with secondary hyperparathyroidism. We then asked whether normal parathyroid cells exhibit L-type Ca²⁺ channel activity. The normal parathyroid cells, loaded with either fluo-3AM or fluo-4AM, were bathed in Hepes-buffered solution containing 1.5 or 2.0 mM Ca²⁺. Fluorescence signal was detected with a Nipkow-type confocal microscopy system. Pressure-application (10 s) of the solution containing either 150 mM K⁺ or 2.5-3.0 mM Ca²⁺ evoked a transient increase in fluo-3 or fluo-4 fluorescence (Ca²⁺ transient). In nominally Ca²⁺-free solution, the high-K⁺ solution failed to evoke the Ca²⁺ transient. In the presence of 10 μM nitrendipine or nicardipine, both high-K⁺-induced Ca²⁺ transients and high-Ca²⁺-induced Ca²⁺ transients were strongly inhibited. Similar inhibitory effects were observed in the presence of 0.2-0.5 mM Cd²⁺. In contrast, FPL64176, an L-type Ca²⁺ channel agonist, significantly enhanced high-K⁺-induced Ca²⁺ transients in 1.2-1.5 mM extracellular Ca²⁺. These results suggest that L-type Ca²⁺ channels provide a pathway for extracellular Ca²⁺ entry in hyperplasic and normal parathyroid cells. [J Physiol Sci. 2007;57 Suppl:S173]