Effects of parathyroid hormone on cytosolic calcium in renal proximal tubular primary cultures

The effects of parathyroid hormone on the cytoplasmic Ca²⁺ concentration of canine renal proximal tubule cells grown in primary culture were determined using the fluorescent Ca²⁺ indicator quin 2. The cultured cells exhibited responses to hormones, enzyme activities, transport functions, and morphology characteristic of the proximal convoluted tubule. Parathyroid hormone stimulated an immediate rise in cytoplasmic Ca²⁺, both in suspended cells and cells studied as a monolayer on Nucleopore filters. The rise in cytoplasmic Ca²⁺ induced by the hormone was sustained for 15-30 min, was dose dependent, and was not mimicked by cyclic AMP. Removing Ca²⁺ from the extracellular media markedly decreased cytoplasmic Ca²⁺ and abolished the effects of parathyroid hormone on cytosolic Ca²⁺. 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate blocked the effects of the hormone on cytosolic Ca²⁺, but mitochondrial uncouplers failed to inhibit the effects of the hormone to increase cytoplasmic Ca²⁺. These studies support a role of Ca²⁺ in the activation of proximal renal tubule cells by parathyroid hormone.