Abstract
To delineate pathways for "signal" transduction by growth hormone (GH) in proximal tubule, we incubated basolateral membranes isolated from canine kidney with human growth hormone (hGH) or human prolactin (hPrl) and measured levels of inositol trisphosphate (InsP3) in suspensions and of diacylglycerol extractable from the membranes. Incubation with hGH, but not hPrl, increased levels of InsP3 and diacylglycerol in a concentration-dependent manner. Half-maximal effects occurred between 0.1 and 1 nM hGH. Increased levels of InsP3 were measured after as little as 5 sec of incubation with 1 nM hGH, and increase was maximal after 15 sec. Increases were no longer detectable after 60 sec because of dephosphorylation of InsP3 in membrane suspensions. hGH did not affect rates of dephosphorylation. hGH-stimulated increases in InsP3 were detectable in membranes suspended in 0, 0.1, and 0.2 mM calcium but not in 0.3 or 1.0 microMs calcium. 125I-labeled hGH-receptor complexes with Mr values of 66,000 and 140,000 were identified in isolated basolateral membranes. Our findings establish that GH activates phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) in isolated canine renal proximal tubular basolateral membranes, potentially after binding to a specific receptor. This process could mediate "signal" transmission by GH across the plasma membrane of the proximal tubular cell and elsewhere.