HORMONE-MEDIATED CA2+ TRANSIENTS IN ISOLATED RENAL CORTICAL THICK ASCENDING LIMB CELLS

Peptide hormones control salt reabsorption in cortical thick ascending limb (cTAL) cells of the loop of Henle. These agonists act, in part, through alterations on intracellular Ca2+ ([Ca2+](i)). Primary cell cultures were prepared from porcine kidneys using a double antibody technique (goat antihuman Tamm-Horsfall and rabbit antigoat IgG antibodies). [Ca2+](i) was determined in single cells with fluorescent techniques using fura-2. Parathyroid hormone (PTH) and arginine vasopressin (AVP) transiently increased [Ca2+](i) in a dose-dependent manner. [Ca2+](i) maximally increased from 85+/-5 nmol/l to 608+/-99 nmol/l with PTH, 10(-6) M, and to 766+/-162 nmol/l with AVP, 10(-7) M. The increment in [Ca2+](i) by both hormones was by intracellular Ca2+ release and entry through plasma membrane Ca2+ channels. 8-Bromoadenosine-3',5'-cyclic monophosphate (8-BrcAMP), 10(-4) M, increased [Ca2+](i) (basal 83+/-3 to 427+/-121 nmol/l) but only from internal sources as nifedipine (10 mu mol), ([Ca2+](i) changes: 86+/-4 to 390+/-29 nmol/l) and removal of bath Ca2+, ([Ca2+](i) changes: 84+/-6 to 517+/-142 nmol/l), were without effect on agonist-induced [Ca2+](i). Thapsigargin, 1.5 mu mol, completely abolished the AVP- and cyclic adenosine monophosphate(cAMP)-induced Ca2+ transients, and partially inhibited PTH-mediated Ca2+ transients by about 50%. Pretreatment with 8-BrcAMP inhibited the PTH and AVP responses likely through depletion of cAMP-sensitive Ca2+ stores. Activation of protein kinase C (PKC) with phorbol esters inhibited PTH and AVP responses and 8-BrcAMP-induced [Ca2+](i) transients. The responses partially returned following down-regulation of PKC with prolonged exposure to phorbol esters. These data suggest that PKC activation modulates agonist-induced Ca2+ release and entry, possibly through actions on intracellular release mechanisms. In summary, PTH and AVP stimulate Ca2+ signals by similar pathways involving cAMP and inositol 1,3,4-trisphosphate activity at similar sites on the endoplasmic reticulum and plasma membrane. These results suggest that peptide hormones may act through Ca2+ and be modulated by different pathways which may have diverse effects on cTAL function.