Objective Venous function is underappreciated in its role in blood pressure determination, a physiological parameter normally ascribed to changes in arterial function. Significant evidence points to the hormone endothelin-1 (ET-1) as being important to venous contributions to blood pressure. We hypothesized that the artery and vein should similarly depend on the signaling pathways stimulated by ET-1, specifically phospholipase C (PLC) activation. This produces two functional arms of signaling: diacylglycerol (DAG; protein kinase C activation) and inositol trisphosphate (IP3) production (intracellular calcium release). Methods The model was the male Sprague Dawley rat. Isolated tissue baths were used to measure isometric contraction. Western blot and immunocytochemical analyses measured the magnitude of expression and site of expression, respectively, of IP3 receptors in smooth muscle/tissue. Pharmacological methods were used to modify phospholipase C activity and signaling elements downstream of phospholipase C (IP3 receptors, protein kinase C). Results ET-1-induced contraction was phospholipase C-dependent in both tissues as the phospholipase C inhibitor U73122 significantly reduced contraction in aorta (86±4% of control, P<.05) and vena cava (49±11% of control, P<.05). However, ET-1-induced contraction was not significantly inhibited by the IP3 receptor inhibitor 2-APB (100 μM) in vena cava (82±8% of control, P=.23) but was in the aorta (55±4% of control, P<.05). All three IP3 receptor isoforms were located in venous smooth muscle. IP3 receptors were functional in both tissues as the novel membrane-permeable IP3 analogue (Bt-IP3; 10μM) contracted aorta and vena cava. Similarly, while the PKC inhibitor chelerythrine (10μM) attenuated ET-1-induced contraction in vena cava and aorta (5±2% and 50±5% of control, respectively; P<.05), only the vena cava contracted to the DAG analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG). Conclusions These findings suggest that ET-1 activates phospholipase C in aorta and vena cava, but vena cava contraction to ET-1 may be largely IP3-independent. Rather, DAG – not IP3 – may contribute to contraction to ET-1 in vena cava, in part by activation of protein kinase C. These studies outline a fundamental difference between venous and arterial smooth muscle and further reinforce a heterogeneity of vascular smooth muscle function that could be taken advantage of for therapeutic development.

A 9-y-old, castrated male, domestic medium-hair cat diagnosed previously with chronic kidney disease developed anorexia and vomiting. Ultrasonography revealed abdominal effusion and a left renal perihilar mass. Cytologic evaluation of the peritoneal fluid and mass identified atypical epithelioid cells suspected to be of renal epithelial or possible mesothelial origin. Immunohistochemical (IHC) evaluation of a formalin-fixed, paraffin-embedded peritoneal fluid cell block indicated both pancytokeratin and vimentin expression in the atypical epithelioid cell population. With scanning electron microscopic evaluation, similar epithelioid cells lacked the cell-surface microvilli expected of mesothelium, supporting an antemortem diagnosis of probable carcinoma. On postmortem examination, the left kidney was effaced by an infiltrative neoplasm with myriad similar nodules throughout the peritoneum. The neoplasm was composed primarily of polygonal-to-spindle-shaped cells with strong vimentin and weak pancytokeratin cytoplasmic immunolabeling. Further IHC characterization with PAX8, CK18, KIT, napsin A, SMA, desmin, CD18, and claudin 5 was performed. Histologic and IHC findings supported a diagnosis of sarcomatoid renal cell carcinoma with peritoneal carcinomatosis. An in vitro cell culture line of neoplastic cells harvested from the primary tumor was successfully established for future research endeavors.

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In vascular smooth muscle, inositol 1,4,5‐trisphosphate (IP3) regulates excitation‐contraction coupling by activating the release of sarcoplasmic Ca2+ stores. IP3 is produced through the activity of phospholipase Cβ (PLCβ), which cleaves phosphatidylinositol into diacylglycerol (DAG) and IP3. While the vasoconstrictor ET‐1 activates PLCβ and increases IP3 formation in arteries, it is unclear if this is so in veins. We hypothesized that contraction to ET‐1 in rat aorta (RA) and vena cava (RVC) depends upon IP3‐mediated Ca2+ release. To test if PLCβ was activated by ET‐1, isometric contraction was measured in RA and RVC rings exposed to vehicle, the PLCβ inhibitor U‐73122 or its inactive analog U‐ 73343 (1 μM), or the IP3 receptor antagonist 2‐APB (100 μM). While U‐73343 did not significantly inhibit contraction to ET‐1, U‐73122 significantly reduced maximum contraction to ET‐1 in RA (86±6% of control) and RVC (49±11% of control). Contrary to our hypothesis, 2‐APB significantly reduced maximum contraction to ET‐1 only in RA (55±4%) and not RVC (82±8%). These data were supported by Western blot analysis, showing 63.1 times more IP3R‐1 and 12.6 times more IP3R‐2 protein in RA than RVC, as measured by densitometry. These findings suggest that ET‐1 does activate PLCβ in RA and RVC, but only contraction to ET‐1 in RA is regulated by IP3. Rather, DAG and not IP3 may regulate contraction to ET‐1 in RVC. Supported by NIH P01HL70687.