Vasopressin-induced increases of cytosolic calcium in LLC-PK1 cells

LLC-PK1 cells, a permanent cell line of renal tubule origin, which has vasopressin (VP) receptors and an adenosine 3',5'-cyclic monophosphate (cAMP) response to VP were grown to confluence on glass cover slips and loaded for 30-45 min with fura-2. Exposure to fura-2 did not affect cell viability (greater than 99%), K+, or ATP levels. Free cytosolic Ca2+ (Caf) was estimated spectrofluorometrically on washed cover slips. Basal levels averaged 73 +/- 3 nM. Peak Caf levels induced were: 10(-8) M VP - 128 +/- 24 nM, 10(-7) M VP - 301 +/- 51 nM, 10(-6) M VP - 537 +/- 117 nM. Peak Caf after 10(-6) M VP was reached in 42 +/- 5 s, followed by a return toward basal levels. Addition of a second dose of 10(-6) M VP following an initial dose of 10(-6) M VP did not raise Caf. Chelation of medium Ca2+ with ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid just prior to 10(-6) M VP did not reduce the response of Caf (peak of 359 +/- 53). In contrast to VP, 10(-6) M calcitonin and PTH did not significantly increase Caf. The response to 10(-6) M VP was not significantly modified by prior prostaglandin E2 (3 microM) or dibutyryl-cAMP (100 microM). The response to 1-desamino-8-D-arginine vasopressin was less than that to VP. However, studies with VP-receptor antagonists did not allow definitive delineation of receptor type. These data provide evidence for VP-induced increases of Caf via release from intracellular stores in a renal epithelial cell.